<!-- doc/src/sgml/func.sgml -->
<chapter id="functions">
<title>Functions and Operators</title>
<indexterm zone="functions">
<primary>function</primary>
</indexterm>
<indexterm zone="functions">
<primary>operator</primary>
</indexterm>
<para>
<productname>PostgreSQL</productname> provides a large number of
functions and operators for the built-in data types. This chapter
describes most of them, although additional special-purpose functions
appear in relevant sections of the manual. Users can also
define their own functions and operators, as described in
<xref linkend="server-programming"/>. The
<application>psql</application> commands <command>\df</command> and
<command>\do</command> can be used to list all
available functions and operators, respectively.
</para>
<para>
The notation used throughout this chapter to describe the argument and
result data types of a function or operator is like this:
<synopsis>
<function>repeat</function> ( <type>text</type>, <type>integer</type> ) <returnvalue>text</returnvalue>
</synopsis>
which says that the function <function>repeat</function> takes one text and
one integer argument and returns a result of type text. The right arrow
is also used to indicate the result of an example, thus:
<programlisting>
repeat('Pg', 4) <returnvalue>PgPgPgPg</returnvalue>
</programlisting>
</para>
<para>
If you are concerned about portability then note that most of
the functions and operators described in this chapter, with the
exception of the most trivial arithmetic and comparison operators
and some explicitly marked functions, are not specified by the
<acronym>SQL</acronym> standard. Some of this extended functionality
is present in other <acronym>SQL</acronym> database management
systems, and in many cases this functionality is compatible and
consistent between the various implementations.
</para>
<sect1 id="functions-logical">
<title>Logical Operators</title>
<indexterm zone="functions-logical">
<primary>operator</primary>
<secondary>logical</secondary>
</indexterm>
<indexterm>
<primary>Boolean</primary>
<secondary>operators</secondary>
<see>operators, logical</see>
</indexterm>
<para>
The usual logical operators are available:
<indexterm>
<primary>AND (operator)</primary>
</indexterm>
<indexterm>
<primary>OR (operator)</primary>
</indexterm>
<indexterm>
<primary>NOT (operator)</primary>
</indexterm>
<indexterm>
<primary>conjunction</primary>
</indexterm>
<indexterm>
<primary>disjunction</primary>
</indexterm>
<indexterm>
<primary>negation</primary>
</indexterm>
<synopsis>
<type>boolean</type> <literal>AND</literal> <type>boolean</type> <returnvalue>boolean</returnvalue>
<type>boolean</type> <literal>OR</literal> <type>boolean</type> <returnvalue>boolean</returnvalue>
<literal>NOT</literal> <type>boolean</type> <returnvalue>boolean</returnvalue>
</synopsis>
<acronym>SQL</acronym> uses a three-valued logic system with true,
false, and <literal>null</literal>, which represents <quote>unknown</quote>.
Observe the following truth tables:
<informaltable>
<tgroup cols="4">
<thead>
<row>
<entry><replaceable>a</replaceable></entry>
<entry><replaceable>b</replaceable></entry>
<entry><replaceable>a</replaceable> AND <replaceable>b</replaceable></entry>
<entry><replaceable>a</replaceable> OR <replaceable>b</replaceable></entry>
</row>
</thead>
<tbody>
<row>
<entry>TRUE</entry>
<entry>TRUE</entry>
<entry>TRUE</entry>
<entry>TRUE</entry>
</row>
<row>
<entry>TRUE</entry>
<entry>FALSE</entry>
<entry>FALSE</entry>
<entry>TRUE</entry>
</row>
<row>
<entry>TRUE</entry>
<entry>NULL</entry>
<entry>NULL</entry>
<entry>TRUE</entry>
</row>
<row>
<entry>FALSE</entry>
<entry>FALSE</entry>
<entry>FALSE</entry>
<entry>FALSE</entry>
</row>
<row>
<entry>FALSE</entry>
<entry>NULL</entry>
<entry>FALSE</entry>
<entry>NULL</entry>
</row>
<row>
<entry>NULL</entry>
<entry>NULL</entry>
<entry>NULL</entry>
<entry>NULL</entry>
</row>
</tbody>
</tgroup>
</informaltable>
<informaltable>
<tgroup cols="2">
<thead>
<row>
<entry><replaceable>a</replaceable></entry>
<entry>NOT <replaceable>a</replaceable></entry>
</row>
</thead>
<tbody>
<row>
<entry>TRUE</entry>
<entry>FALSE</entry>
</row>
<row>
<entry>FALSE</entry>
<entry>TRUE</entry>
</row>
<row>
<entry>NULL</entry>
<entry>NULL</entry>
</row>
</tbody>
</tgroup>
</informaltable>
</para>
<para>
The operators <literal>AND</literal> and <literal>OR</literal> are
commutative, that is, you can switch the left and right operands
without affecting the result. (However, it is not guaranteed that
the left operand is evaluated before the right operand. See <xref
linkend="syntax-express-eval"/> for more information about the
order of evaluation of subexpressions.)
</para>
</sect1>
<sect1 id="functions-comparison">
<title>Comparison Functions and Operators</title>
<indexterm zone="functions-comparison">
<primary>comparison</primary>
<secondary>operators</secondary>
</indexterm>
<para>
The usual comparison operators are available, as shown in <xref
linkend="functions-comparison-op-table"/>.
</para>
<table id="functions-comparison-op-table">
<title>Comparison Operators</title>
<tgroup cols="2">
<thead>
<row>
<entry>Operator</entry>
<entry>Description</entry>
</row>
</thead>
<tbody>
<row>
<entry>
<replaceable>datatype</replaceable> <literal><</literal> <replaceable>datatype</replaceable>
<returnvalue>boolean</returnvalue>
</entry>
<entry>Less than</entry>
</row>
<row>
<entry>
<replaceable>datatype</replaceable> <literal>></literal> <replaceable>datatype</replaceable>
<returnvalue>boolean</returnvalue>
</entry>
<entry>Greater than</entry>
</row>
<row>
<entry>
<replaceable>datatype</replaceable> <literal><=</literal> <replaceable>datatype</replaceable>
<returnvalue>boolean</returnvalue>
</entry>
<entry>Less than or equal to</entry>
</row>
<row>
<entry>
<replaceable>datatype</replaceable> <literal>>=</literal> <replaceable>datatype</replaceable>
<returnvalue>boolean</returnvalue>
</entry>
<entry>Greater than or equal to</entry>
</row>
<row>
<entry>
<replaceable>datatype</replaceable> <literal>=</literal> <replaceable>datatype</replaceable>
<returnvalue>boolean</returnvalue>
</entry>
<entry>Equal</entry>
</row>
<row>
<entry>
<replaceable>datatype</replaceable> <literal><></literal> <replaceable>datatype</replaceable>
<returnvalue>boolean</returnvalue>
</entry>
<entry>Not equal</entry>
</row>
<row>
<entry>
<replaceable>datatype</replaceable> <literal>!=</literal> <replaceable>datatype</replaceable>
<returnvalue>boolean</returnvalue>
</entry>
<entry>Not equal</entry>
</row>
</tbody>
</tgroup>
</table>
<note>
<para>
<literal><></literal> is the standard SQL notation for <quote>not
equal</quote>. <literal>!=</literal> is an alias, which is converted
to <literal><></literal> at a very early stage of parsing.
Hence, it is not possible to implement <literal>!=</literal>
and <literal><></literal> operators that do different things.
</para>
</note>
<para>
These comparison operators are available for all built-in data types
that have a natural ordering, including numeric, string, and date/time
types. In addition, arrays, composite types, and ranges can be compared
if their component data types are comparable.
</para>
<para>
It is usually possible to compare values of related data
types as well; for example <type>integer</type> <literal>></literal>
<type>bigint</type> will work. Some cases of this sort are implemented
directly by <quote>cross-type</quote> comparison operators, but if no
such operator is available, the parser will coerce the less-general type
to the more-general type and apply the latter's comparison operator.
</para>
<para>
As shown above, all comparison operators are binary operators that
return values of type <type>boolean</type>. Thus, expressions like
<literal>1 < 2 < 3</literal> are not valid (because there is
no <literal><</literal> operator to compare a Boolean value with
<literal>3</literal>). Use the <literal>BETWEEN</literal> predicates
shown below to perform range tests.
</para>
<para>
There are also some comparison predicates, as shown in <xref
linkend="functions-comparison-pred-table"/>. These behave much like
operators, but have special syntax mandated by the SQL standard.
</para>
<table id="functions-comparison-pred-table">
<title>Comparison Predicates</title>
<tgroup cols="1">
<thead>
<row>
<entry role="func_table_entry"><para role="func_signature">
Predicate
</para>
<para>
Description
</para>
<para>
Example(s)
</para></entry>
</row>
</thead>
<tbody>
<row>
<entry role="func_table_entry"><para role="func_signature">
<replaceable>datatype</replaceable> <literal>BETWEEN</literal> <replaceable>datatype</replaceable> <literal>AND</literal> <replaceable>datatype</replaceable>
<returnvalue>boolean</returnvalue>
</para>
<para>
Between (inclusive of the range endpoints).
</para>
<para>
<literal>2 BETWEEN 1 AND 3</literal>
<returnvalue>t</returnvalue>
</para>
<para>
<literal>2 BETWEEN 3 AND 1</literal>
<returnvalue>f</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<replaceable>datatype</replaceable> <literal>NOT BETWEEN</literal> <replaceable>datatype</replaceable> <literal>AND</literal> <replaceable>datatype</replaceable>
<returnvalue>boolean</returnvalue>
</para>
<para>
Not between (the negation of <literal>BETWEEN</literal>).
</para>
<para>
<literal>2 NOT BETWEEN 1 AND 3</literal>
<returnvalue>f</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<replaceable>datatype</replaceable> <literal>BETWEEN SYMMETRIC</literal> <replaceable>datatype</replaceable> <literal>AND</literal> <replaceable>datatype</replaceable>
<returnvalue>boolean</returnvalue>
</para>
<para>
Between, after sorting the two endpoint values.
</para>
<para>
<literal>2 BETWEEN SYMMETRIC 3 AND 1</literal>
<returnvalue>t</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<replaceable>datatype</replaceable> <literal>NOT BETWEEN SYMMETRIC</literal> <replaceable>datatype</replaceable> <literal>AND</literal> <replaceable>datatype</replaceable>
<returnvalue>boolean</returnvalue>
</para>
<para>
Not between, after sorting the two endpoint values.
</para>
<para>
<literal>2 NOT BETWEEN SYMMETRIC 3 AND 1</literal>
<returnvalue>f</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<replaceable>datatype</replaceable> <literal>IS DISTINCT FROM</literal> <replaceable>datatype</replaceable>
<returnvalue>boolean</returnvalue>
</para>
<para>
Not equal, treating null as a comparable value.
</para>
<para>
<literal>1 IS DISTINCT FROM NULL</literal>
<returnvalue>t</returnvalue> (rather than <literal>NULL</literal>)
</para>
<para>
<literal>NULL IS DISTINCT FROM NULL</literal>
<returnvalue>f</returnvalue> (rather than <literal>NULL</literal>)
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<replaceable>datatype</replaceable> <literal>IS NOT DISTINCT FROM</literal> <replaceable>datatype</replaceable>
<returnvalue>boolean</returnvalue>
</para>
<para>
Equal, treating null as a comparable value.
</para>
<para>
<literal>1 IS NOT DISTINCT FROM NULL</literal>
<returnvalue>f</returnvalue> (rather than <literal>NULL</literal>)
</para>
<para>
<literal>NULL IS NOT DISTINCT FROM NULL</literal>
<returnvalue>t</returnvalue> (rather than <literal>NULL</literal>)
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<replaceable>datatype</replaceable> <literal>IS NULL</literal>
<returnvalue>boolean</returnvalue>
</para>
<para>
Test whether value is null.
</para>
<para>
<literal>1.5 IS NULL</literal>
<returnvalue>f</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<replaceable>datatype</replaceable> <literal>IS NOT NULL</literal>
<returnvalue>boolean</returnvalue>
</para>
<para>
Test whether value is not null.
</para>
<para>
<literal>'null' IS NOT NULL</literal>
<returnvalue>t</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<replaceable>datatype</replaceable> <literal>ISNULL</literal>
<returnvalue>boolean</returnvalue>
</para>
<para>
Test whether value is null (nonstandard syntax).
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<replaceable>datatype</replaceable> <literal>NOTNULL</literal>
<returnvalue>boolean</returnvalue>
</para>
<para>
Test whether value is not null (nonstandard syntax).
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<type>boolean</type> <literal>IS TRUE</literal>
<returnvalue>boolean</returnvalue>
</para>
<para>
Test whether boolean expression yields true.
</para>
<para>
<literal>true IS TRUE</literal>
<returnvalue>t</returnvalue>
</para>
<para>
<literal>NULL::boolean IS TRUE</literal>
<returnvalue>f</returnvalue> (rather than <literal>NULL</literal>)
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<type>boolean</type> <literal>IS NOT TRUE</literal>
<returnvalue>boolean</returnvalue>
</para>
<para>
Test whether boolean expression yields false or unknown.
</para>
<para>
<literal>true IS NOT TRUE</literal>
<returnvalue>f</returnvalue>
</para>
<para>
<literal>NULL::boolean IS NOT TRUE</literal>
<returnvalue>t</returnvalue> (rather than <literal>NULL</literal>)
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<type>boolean</type> <literal>IS FALSE</literal>
<returnvalue>boolean</returnvalue>
</para>
<para>
Test whether boolean expression yields false.
</para>
<para>
<literal>true IS FALSE</literal>
<returnvalue>f</returnvalue>
</para>
<para>
<literal>NULL::boolean IS FALSE</literal>
<returnvalue>f</returnvalue> (rather than <literal>NULL</literal>)
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<type>boolean</type> <literal>IS NOT FALSE</literal>
<returnvalue>boolean</returnvalue>
</para>
<para>
Test whether boolean expression yields true or unknown.
</para>
<para>
<literal>true IS NOT FALSE</literal>
<returnvalue>t</returnvalue>
</para>
<para>
<literal>NULL::boolean IS NOT FALSE</literal>
<returnvalue>t</returnvalue> (rather than <literal>NULL</literal>)
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<type>boolean</type> <literal>IS UNKNOWN</literal>
<returnvalue>boolean</returnvalue>
</para>
<para>
Test whether boolean expression yields unknown.
</para>
<para>
<literal>true IS UNKNOWN</literal>
<returnvalue>f</returnvalue>
</para>
<para>
<literal>NULL::boolean IS UNKNOWN</literal>
<returnvalue>t</returnvalue> (rather than <literal>NULL</literal>)
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<type>boolean</type> <literal>IS NOT UNKNOWN</literal>
<returnvalue>boolean</returnvalue>
</para>
<para>
Test whether boolean expression yields true or false.
</para>
<para>
<literal>true IS NOT UNKNOWN</literal>
<returnvalue>t</returnvalue>
</para>
<para>
<literal>NULL::boolean IS NOT UNKNOWN</literal>
<returnvalue>f</returnvalue> (rather than <literal>NULL</literal>)
</para></entry>
</row>
</tbody>
</tgroup>
</table>
<para>
<indexterm>
<primary>BETWEEN</primary>
</indexterm>
<indexterm>
<primary>BETWEEN SYMMETRIC</primary>
</indexterm>
The <token>BETWEEN</token> predicate simplifies range tests:
<synopsis>
<replaceable>a</replaceable> BETWEEN <replaceable>x</replaceable> AND <replaceable>y</replaceable>
</synopsis>
is equivalent to
<synopsis>
<replaceable>a</replaceable> >= <replaceable>x</replaceable> AND <replaceable>a</replaceable> <= <replaceable>y</replaceable>
</synopsis>
Notice that <token>BETWEEN</token> treats the endpoint values as included
in the range.
<literal>BETWEEN SYMMETRIC</literal> is like <literal>BETWEEN</literal>
except there is no requirement that the argument to the left of
<literal>AND</literal> be less than or equal to the argument on the right.
If it is not, those two arguments are automatically swapped, so that
a nonempty range is always implied.
</para>
<para>
The various variants of <literal>BETWEEN</literal> are implemented in
terms of the ordinary comparison operators, and therefore will work for
any data type(s) that can be compared.
</para>
<note>
<para>
The use of <literal>AND</literal> in the <literal>BETWEEN</literal>
syntax creates an ambiguity with the use of <literal>AND</literal> as a
logical operator. To resolve this, only a limited set of expression
types are allowed as the second argument of a <literal>BETWEEN</literal>
clause. If you need to write a more complex sub-expression
in <literal>BETWEEN</literal>, write parentheses around the
sub-expression.
</para>
</note>
<para>
<indexterm>
<primary>IS DISTINCT FROM</primary>
</indexterm>
<indexterm>
<primary>IS NOT DISTINCT FROM</primary>
</indexterm>
Ordinary comparison operators yield null (signifying <quote>unknown</quote>),
not true or false, when either input is null. For example,
<literal>7 = NULL</literal> yields null, as does <literal>7 <> NULL</literal>. When
this behavior is not suitable, use the
<literal>IS <optional> NOT </optional> DISTINCT FROM</literal> predicates:
<synopsis>
<replaceable>a</replaceable> IS DISTINCT FROM <replaceable>b</replaceable>
<replaceable>a</replaceable> IS NOT DISTINCT FROM <replaceable>b</replaceable>
</synopsis>
For non-null inputs, <literal>IS DISTINCT FROM</literal> is
the same as the <literal><></literal> operator. However, if both
inputs are null it returns false, and if only one input is
null it returns true. Similarly, <literal>IS NOT DISTINCT
FROM</literal> is identical to <literal>=</literal> for non-null
inputs, but it returns true when both inputs are null, and false when only
one input is null. Thus, these predicates effectively act as though null
were a normal data value, rather than <quote>unknown</quote>.
</para>
<para>
<indexterm>
<primary>IS NULL</primary>
</indexterm>
<indexterm>
<primary>IS NOT NULL</primary>
</indexterm>
<indexterm>
<primary>ISNULL</primary>
</indexterm>
<indexterm>
<primary>NOTNULL</primary>
</indexterm>
To check whether a value is or is not null, use the predicates:
<synopsis>
<replaceable>expression</replaceable> IS NULL
<replaceable>expression</replaceable> IS NOT NULL
</synopsis>
or the equivalent, but nonstandard, predicates:
<synopsis>
<replaceable>expression</replaceable> ISNULL
<replaceable>expression</replaceable> NOTNULL
</synopsis>
<indexterm><primary>null value</primary><secondary>comparing</secondary></indexterm>
</para>
<para>
Do <emphasis>not</emphasis> write
<literal><replaceable>expression</replaceable> = NULL</literal>
because <literal>NULL</literal> is not <quote>equal to</quote>
<literal>NULL</literal>. (The null value represents an unknown value,
and it is not known whether two unknown values are equal.)
</para>
<tip>
<para>
Some applications might expect that
<literal><replaceable>expression</replaceable> = NULL</literal>
returns true if <replaceable>expression</replaceable> evaluates to
the null value. It is highly recommended that these applications
be modified to comply with the SQL standard. However, if that
cannot be done the <xref linkend="guc-transform-null-equals"/>
configuration variable is available. If it is enabled,
<productname>PostgreSQL</productname> will convert <literal>x =
NULL</literal> clauses to <literal>x IS NULL</literal>.
</para>
</tip>
<para>
If the <replaceable>expression</replaceable> is row-valued, then
<literal>IS NULL</literal> is true when the row expression itself is null
or when all the row's fields are null, while
<literal>IS NOT NULL</literal> is true when the row expression itself is non-null
and all the row's fields are non-null. Because of this behavior,
<literal>IS NULL</literal> and <literal>IS NOT NULL</literal> do not always return
inverse results for row-valued expressions; in particular, a row-valued
expression that contains both null and non-null fields will return false
for both tests. In some cases, it may be preferable to
write <replaceable>row</replaceable> <literal>IS DISTINCT FROM NULL</literal>
or <replaceable>row</replaceable> <literal>IS NOT DISTINCT FROM NULL</literal>,
which will simply check whether the overall row value is null without any
additional tests on the row fields.
</para>
<para>
<indexterm>
<primary>IS TRUE</primary>
</indexterm>
<indexterm>
<primary>IS NOT TRUE</primary>
</indexterm>
<indexterm>
<primary>IS FALSE</primary>
</indexterm>
<indexterm>
<primary>IS NOT FALSE</primary>
</indexterm>
<indexterm>
<primary>IS UNKNOWN</primary>
</indexterm>
<indexterm>
<primary>IS NOT UNKNOWN</primary>
</indexterm>
Boolean values can also be tested using the predicates
<synopsis>
<replaceable>boolean_expression</replaceable> IS TRUE
<replaceable>boolean_expression</replaceable> IS NOT TRUE
<replaceable>boolean_expression</replaceable> IS FALSE
<replaceable>boolean_expression</replaceable> IS NOT FALSE
<replaceable>boolean_expression</replaceable> IS UNKNOWN
<replaceable>boolean_expression</replaceable> IS NOT UNKNOWN
</synopsis>
These will always return true or false, never a null value, even when the
operand is null.
A null input is treated as the logical value <quote>unknown</quote>.
Notice that <literal>IS UNKNOWN</literal> and <literal>IS NOT UNKNOWN</literal> are
effectively the same as <literal>IS NULL</literal> and
<literal>IS NOT NULL</literal>, respectively, except that the input
expression must be of Boolean type.
</para>
<para>
Some comparison-related functions are also available, as shown in <xref
linkend="functions-comparison-func-table"/>.
</para>
<table id="functions-comparison-func-table">
<title>Comparison Functions</title>
<tgroup cols="1">
<thead>
<row>
<entry role="func_table_entry"><para role="func_signature">
Function
</para>
<para>
Description
</para>
<para>
Example(s)
</para></entry>
</row>
</thead>
<tbody>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>num_nonnulls</primary>
</indexterm>
<function>num_nonnulls</function> ( <literal>VARIADIC</literal> <type>"any"</type> )
<returnvalue>integer</returnvalue>
</para>
<para>
Returns the number of non-null arguments.
</para>
<para>
<literal>num_nonnulls(1, NULL, 2)</literal>
<returnvalue>2</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>num_nulls</primary>
</indexterm>
<function>num_nulls</function> ( <literal>VARIADIC</literal> <type>"any"</type> )
<returnvalue>integer</returnvalue>
</para>
<para>
Returns the number of null arguments.
</para>
<para>
<literal>num_nulls(1, NULL, 2)</literal>
<returnvalue>1</returnvalue>
</para></entry>
</row>
</tbody>
</tgroup>
</table>
</sect1>
<sect1 id="functions-math">
<title>Mathematical Functions and Operators</title>
<para>
Mathematical operators are provided for many
<productname>PostgreSQL</productname> types. For types without
standard mathematical conventions
(e.g., date/time types) we
describe the actual behavior in subsequent sections.
</para>
<para>
<xref linkend="functions-math-op-table"/> shows the mathematical
operators that are available for the standard numeric types.
Unless otherwise noted, operators shown as
accepting <replaceable>numeric_type</replaceable> are available for all
the types <type>smallint</type>, <type>integer</type>,
<type>bigint</type>, <type>numeric</type>, <type>real</type>,
and <type>double precision</type>.
Operators shown as accepting <replaceable>integral_type</replaceable>
are available for the types <type>smallint</type>, <type>integer</type>,
and <type>bigint</type>.
Except where noted, each form of an operator returns the same data type
as its argument(s). Calls involving multiple argument data types, such
as <type>integer</type> <literal>+</literal> <type>numeric</type>,
are resolved by using the type appearing later in these lists.
</para>
<table id="functions-math-op-table">
<title>Mathematical Operators</title>
<tgroup cols="1">
<thead>
<row>
<entry role="func_table_entry"><para role="func_signature">
Operator
</para>
<para>
Description
</para>
<para>
Example(s)
</para></entry>
</row>
</thead>
<tbody>
<row>
<entry role="func_table_entry"><para role="func_signature">
<replaceable>numeric_type</replaceable> <literal>+</literal> <replaceable>numeric_type</replaceable>
<returnvalue><replaceable>numeric_type</replaceable></returnvalue>
</para>
<para>
Addition
</para>
<para>
<literal>2 + 3</literal>
<returnvalue>5</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<literal>+</literal> <replaceable>numeric_type</replaceable>
<returnvalue><replaceable>numeric_type</replaceable></returnvalue>
</para>
<para>
Unary plus (no operation)
</para>
<para>
<literal>+ 3.5</literal>
<returnvalue>3.5</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<replaceable>numeric_type</replaceable> <literal>-</literal> <replaceable>numeric_type</replaceable>
<returnvalue><replaceable>numeric_type</replaceable></returnvalue>
</para>
<para>
Subtraction
</para>
<para>
<literal>2 - 3</literal>
<returnvalue>-1</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<literal>-</literal> <replaceable>numeric_type</replaceable>
<returnvalue><replaceable>numeric_type</replaceable></returnvalue>
</para>
<para>
Negation
</para>
<para>
<literal>- (-4)</literal>
<returnvalue>4</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<replaceable>numeric_type</replaceable> <literal>*</literal> <replaceable>numeric_type</replaceable>
<returnvalue><replaceable>numeric_type</replaceable></returnvalue>
</para>
<para>
Multiplication
</para>
<para>
<literal>2 * 3</literal>
<returnvalue>6</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<replaceable>numeric_type</replaceable> <literal>/</literal> <replaceable>numeric_type</replaceable>
<returnvalue><replaceable>numeric_type</replaceable></returnvalue>
</para>
<para>
Division (for integral types, division truncates the result towards
zero)
</para>
<para>
<literal>5.0 / 2</literal>
<returnvalue>2.5000000000000000</returnvalue>
</para>
<para>
<literal>5 / 2</literal>
<returnvalue>2</returnvalue>
</para>
<para>
<literal>(-5) / 2</literal>
<returnvalue>-2</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<replaceable>numeric_type</replaceable> <literal>%</literal> <replaceable>numeric_type</replaceable>
<returnvalue><replaceable>numeric_type</replaceable></returnvalue>
</para>
<para>
Modulo (remainder); available for <type>smallint</type>,
<type>integer</type>, <type>bigint</type>, and <type>numeric</type>
</para>
<para>
<literal>5 % 4</literal>
<returnvalue>1</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<type>numeric</type> <literal>^</literal> <type>numeric</type>
<returnvalue>numeric</returnvalue>
</para>
<para role="func_signature">
<type>double precision</type> <literal>^</literal> <type>double precision</type>
<returnvalue>double precision</returnvalue>
</para>
<para>
Exponentiation
</para>
<para>
<literal>2 ^ 3</literal>
<returnvalue>8</returnvalue>
</para>
<para>
Unlike typical mathematical practice, multiple uses of
<literal>^</literal> will associate left to right by default:
</para>
<para>
<literal>2 ^ 3 ^ 3</literal>
<returnvalue>512</returnvalue>
</para>
<para>
<literal>2 ^ (3 ^ 3)</literal>
<returnvalue>134217728</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<literal>|/</literal> <type>double precision</type>
<returnvalue>double precision</returnvalue>
</para>
<para>
Square root
</para>
<para>
<literal>|/ 25.0</literal>
<returnvalue>5</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<literal>||/</literal> <type>double precision</type>
<returnvalue>double precision</returnvalue>
</para>
<para>
Cube root
</para>
<para>
<literal>||/ 64.0</literal>
<returnvalue>4</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<literal>@</literal> <replaceable>numeric_type</replaceable>
<returnvalue><replaceable>numeric_type</replaceable></returnvalue>
</para>
<para>
Absolute value
</para>
<para>
<literal>@ -5.0</literal>
<returnvalue>5</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<replaceable>integral_type</replaceable> <literal>&</literal> <replaceable>integral_type</replaceable>
<returnvalue><replaceable>integral_type</replaceable></returnvalue>
</para>
<para>
Bitwise AND
</para>
<para>
<literal>91 & 15</literal>
<returnvalue>11</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<replaceable>integral_type</replaceable> <literal>|</literal> <replaceable>integral_type</replaceable>
<returnvalue><replaceable>integral_type</replaceable></returnvalue>
</para>
<para>
Bitwise OR
</para>
<para>
<literal>32 | 3</literal>
<returnvalue>35</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<replaceable>integral_type</replaceable> <literal>#</literal> <replaceable>integral_type</replaceable>
<returnvalue><replaceable>integral_type</replaceable></returnvalue>
</para>
<para>
Bitwise exclusive OR
</para>
<para>
<literal>17 # 5</literal>
<returnvalue>20</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<literal>~</literal> <replaceable>integral_type</replaceable>
<returnvalue><replaceable>integral_type</replaceable></returnvalue>
</para>
<para>
Bitwise NOT
</para>
<para>
<literal>~1</literal>
<returnvalue>-2</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<replaceable>integral_type</replaceable> <literal><<</literal> <type>integer</type>
<returnvalue><replaceable>integral_type</replaceable></returnvalue>
</para>
<para>
Bitwise shift left
</para>
<para>
<literal>1 << 4</literal>
<returnvalue>16</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<replaceable>integral_type</replaceable> <literal>>></literal> <type>integer</type>
<returnvalue><replaceable>integral_type</replaceable></returnvalue>
</para>
<para>
Bitwise shift right
</para>
<para>
<literal>8 >> 2</literal>
<returnvalue>2</returnvalue>
</para></entry>
</row>
</tbody>
</tgroup>
</table>
<para>
<xref linkend="functions-math-func-table"/> shows the available
mathematical functions.
Many of these functions are provided in multiple forms with different
argument types.
Except where noted, any given form of a function returns the same
data type as its argument(s); cross-type cases are resolved in the
same way as explained above for operators.
The functions working with <type>double precision</type> data are mostly
implemented on top of the host system's C library; accuracy and behavior in
boundary cases can therefore vary depending on the host system.
</para>
<table id="functions-math-func-table">
<title>Mathematical Functions</title>
<tgroup cols="1">
<thead>
<row>
<entry role="func_table_entry"><para role="func_signature">
Function
</para>
<para>
Description
</para>
<para>
Example(s)
</para></entry>
</row>
</thead>
<tbody>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>abs</primary>
</indexterm>
<function>abs</function> ( <replaceable>numeric_type</replaceable> )
<returnvalue><replaceable>numeric_type</replaceable></returnvalue>
</para>
<para>
Absolute value
</para>
<para>
<literal>abs(-17.4)</literal>
<returnvalue>17.4</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>cbrt</primary>
</indexterm>
<function>cbrt</function> ( <type>double precision</type> )
<returnvalue>double precision</returnvalue>
</para>
<para>
Cube root
</para>
<para>
<literal>cbrt(64.0)</literal>
<returnvalue>4</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>ceil</primary>
</indexterm>
<function>ceil</function> ( <type>numeric</type> )
<returnvalue>numeric</returnvalue>
</para>
<para role="func_signature">
<function>ceil</function> ( <type>double precision</type> )
<returnvalue>double precision</returnvalue>
</para>
<para>
Nearest integer greater than or equal to argument
</para>
<para>
<literal>ceil(42.2)</literal>
<returnvalue>43</returnvalue>
</para>
<para>
<literal>ceil(-42.8)</literal>
<returnvalue>-42</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>ceiling</primary>
</indexterm>
<function>ceiling</function> ( <type>numeric</type> )
<returnvalue>numeric</returnvalue>
</para>
<para role="func_signature">
<function>ceiling</function> ( <type>double precision</type> )
<returnvalue>double precision</returnvalue>
</para>
<para>
Nearest integer greater than or equal to argument (same
as <function>ceil</function>)
</para>
<para>
<literal>ceiling(95.3)</literal>
<returnvalue>96</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>degrees</primary>
</indexterm>
<function>degrees</function> ( <type>double precision</type> )
<returnvalue>double precision</returnvalue>
</para>
<para>
Converts radians to degrees
</para>
<para>
<literal>degrees(0.5)</literal>
<returnvalue>28.64788975654116</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>div</primary>
</indexterm>
<function>div</function> ( <parameter>y</parameter> <type>numeric</type>,
<parameter>x</parameter> <type>numeric</type> )
<returnvalue>numeric</returnvalue>
</para>
<para>
Integer quotient of <parameter>y</parameter>/<parameter>x</parameter>
(truncates towards zero)
</para>
<para>
<literal>div(9, 4)</literal>
<returnvalue>2</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>exp</primary>
</indexterm>
<function>exp</function> ( <type>numeric</type> )
<returnvalue>numeric</returnvalue>
</para>
<para role="func_signature">
<function>exp</function> ( <type>double precision</type> )
<returnvalue>double precision</returnvalue>
</para>
<para>
Exponential (<literal>e</literal> raised to the given power)
</para>
<para>
<literal>exp(1.0)</literal>
<returnvalue>2.7182818284590452</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm id="function-factorial">
<primary>factorial</primary>
</indexterm>
<function>factorial</function> ( <type>bigint</type> )
<returnvalue>numeric</returnvalue>
</para>
<para>
Factorial
</para>
<para>
<literal>factorial(5)</literal>
<returnvalue>120</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>floor</primary>
</indexterm>
<function>floor</function> ( <type>numeric</type> )
<returnvalue>numeric</returnvalue>
</para>
<para role="func_signature">
<function>floor</function> ( <type>double precision</type> )
<returnvalue>double precision</returnvalue>
</para>
<para>
Nearest integer less than or equal to argument
</para>
<para>
<literal>floor(42.8)</literal>
<returnvalue>42</returnvalue>
</para>
<para>
<literal>floor(-42.8)</literal>
<returnvalue>-43</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>gcd</primary>
</indexterm>
<function>gcd</function> ( <replaceable>numeric_type</replaceable>, <replaceable>numeric_type</replaceable> )
<returnvalue><replaceable>numeric_type</replaceable></returnvalue>
</para>
<para>
Greatest common divisor (the largest positive number that divides both
inputs with no remainder); returns <literal>0</literal> if both inputs
are zero; available for <type>integer</type>, <type>bigint</type>,
and <type>numeric</type>
</para>
<para>
<literal>gcd(1071, 462)</literal>
<returnvalue>21</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>lcm</primary>
</indexterm>
<function>lcm</function> ( <replaceable>numeric_type</replaceable>, <replaceable>numeric_type</replaceable> )
<returnvalue><replaceable>numeric_type</replaceable></returnvalue>
</para>
<para>
Least common multiple (the smallest strictly positive number that is
an integral multiple of both inputs); returns <literal>0</literal> if
either input is zero; available for <type>integer</type>,
<type>bigint</type>, and <type>numeric</type>
</para>
<para>
<literal>lcm(1071, 462)</literal>
<returnvalue>23562</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>ln</primary>
</indexterm>
<function>ln</function> ( <type>numeric</type> )
<returnvalue>numeric</returnvalue>
</para>
<para role="func_signature">
<function>ln</function> ( <type>double precision</type> )
<returnvalue>double precision</returnvalue>
</para>
<para>
Natural logarithm
</para>
<para>
<literal>ln(2.0)</literal>
<returnvalue>0.6931471805599453</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>log</primary>
</indexterm>
<function>log</function> ( <type>numeric</type> )
<returnvalue>numeric</returnvalue>
</para>
<para role="func_signature">
<function>log</function> ( <type>double precision</type> )
<returnvalue>double precision</returnvalue>
</para>
<para>
Base 10 logarithm
</para>
<para>
<literal>log(100)</literal>
<returnvalue>2</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>log10</primary>
</indexterm>
<function>log10</function> ( <type>numeric</type> )
<returnvalue>numeric</returnvalue>
</para>
<para role="func_signature">
<function>log10</function> ( <type>double precision</type> )
<returnvalue>double precision</returnvalue>
</para>
<para>
Base 10 logarithm (same as <function>log</function>)
</para>
<para>
<literal>log10(1000)</literal>
<returnvalue>3</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<function>log</function> ( <parameter>b</parameter> <type>numeric</type>,
<parameter>x</parameter> <type>numeric</type> )
<returnvalue>numeric</returnvalue>
</para>
<para>
Logarithm of <parameter>x</parameter> to base <parameter>b</parameter>
</para>
<para>
<literal>log(2.0, 64.0)</literal>
<returnvalue>6.0000000000</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>min_scale</primary>
</indexterm>
<function>min_scale</function> ( <type>numeric</type> )
<returnvalue>integer</returnvalue>
</para>
<para>
Minimum scale (number of fractional decimal digits) needed
to represent the supplied value precisely
</para>
<para>
<literal>min_scale(8.4100)</literal>
<returnvalue>2</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>mod</primary>
</indexterm>
<function>mod</function> ( <parameter>y</parameter> <replaceable>numeric_type</replaceable>,
<parameter>x</parameter> <replaceable>numeric_type</replaceable> )
<returnvalue><replaceable>numeric_type</replaceable></returnvalue>
</para>
<para>
Remainder of <parameter>y</parameter>/<parameter>x</parameter>;
available for <type>smallint</type>, <type>integer</type>,
<type>bigint</type>, and <type>numeric</type>
</para>
<para>
<literal>mod(9, 4)</literal>
<returnvalue>1</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pi</primary>
</indexterm>
<function>pi</function> ( )
<returnvalue>double precision</returnvalue>
</para>
<para>
Approximate value of <phrase role="symbol_font">π</phrase>
</para>
<para>
<literal>pi()</literal>
<returnvalue>3.141592653589793</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>power</primary>
</indexterm>
<function>power</function> ( <parameter>a</parameter> <type>numeric</type>,
<parameter>b</parameter> <type>numeric</type> )
<returnvalue>numeric</returnvalue>
</para>
<para role="func_signature">
<function>power</function> ( <parameter>a</parameter> <type>double precision</type>,
<parameter>b</parameter> <type>double precision</type> )
<returnvalue>double precision</returnvalue>
</para>
<para>
<parameter>a</parameter> raised to the power of <parameter>b</parameter>
</para>
<para>
<literal>power(9, 3)</literal>
<returnvalue>729</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>radians</primary>
</indexterm>
<function>radians</function> ( <type>double precision</type> )
<returnvalue>double precision</returnvalue>
</para>
<para>
Converts degrees to radians
</para>
<para>
<literal>radians(45.0)</literal>
<returnvalue>0.7853981633974483</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>round</primary>
</indexterm>
<function>round</function> ( <type>numeric</type> )
<returnvalue>numeric</returnvalue>
</para>
<para role="func_signature">
<function>round</function> ( <type>double precision</type> )
<returnvalue>double precision</returnvalue>
</para>
<para>
Rounds to nearest integer. For <type>numeric</type>, ties are
broken by rounding away from zero. For <type>double precision</type>,
the tie-breaking behavior is platform dependent, but
<quote>round to nearest even</quote> is the most common rule.
</para>
<para>
<literal>round(42.4)</literal>
<returnvalue>42</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<function>round</function> ( <parameter>v</parameter> <type>numeric</type>, <parameter>s</parameter> <type>integer</type> )
<returnvalue>numeric</returnvalue>
</para>
<para>
Rounds <parameter>v</parameter> to <parameter>s</parameter> decimal
places. Ties are broken by rounding away from zero.
</para>
<para>
<literal>round(42.4382, 2)</literal>
<returnvalue>42.44</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>scale</primary>
</indexterm>
<function>scale</function> ( <type>numeric</type> )
<returnvalue>integer</returnvalue>
</para>
<para>
Scale of the argument (the number of decimal digits in the fractional part)
</para>
<para>
<literal>scale(8.4100)</literal>
<returnvalue>4</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>sign</primary>
</indexterm>
<function>sign</function> ( <type>numeric</type> )
<returnvalue>numeric</returnvalue>
</para>
<para role="func_signature">
<function>sign</function> ( <type>double precision</type> )
<returnvalue>double precision</returnvalue>
</para>
<para>
Sign of the argument (-1, 0, or +1)
</para>
<para>
<literal>sign(-8.4)</literal>
<returnvalue>-1</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>sqrt</primary>
</indexterm>
<function>sqrt</function> ( <type>numeric</type> )
<returnvalue>numeric</returnvalue>
</para>
<para role="func_signature">
<function>sqrt</function> ( <type>double precision</type> )
<returnvalue>double precision</returnvalue>
</para>
<para>
Square root
</para>
<para>
<literal>sqrt(2)</literal>
<returnvalue>1.4142135623730951</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>trim_scale</primary>
</indexterm>
<function>trim_scale</function> ( <type>numeric</type> )
<returnvalue>numeric</returnvalue>
</para>
<para>
Reduces the value's scale (number of fractional decimal digits) by
removing trailing zeroes
</para>
<para>
<literal>trim_scale(8.4100)</literal>
<returnvalue>8.41</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>trunc</primary>
</indexterm>
<function>trunc</function> ( <type>numeric</type> )
<returnvalue>numeric</returnvalue>
</para>
<para role="func_signature">
<function>trunc</function> ( <type>double precision</type> )
<returnvalue>double precision</returnvalue>
</para>
<para>
Truncates to integer (towards zero)
</para>
<para>
<literal>trunc(42.8)</literal>
<returnvalue>42</returnvalue>
</para>
<para>
<literal>trunc(-42.8)</literal>
<returnvalue>-42</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<function>trunc</function> ( <parameter>v</parameter> <type>numeric</type>, <parameter>s</parameter> <type>integer</type> )
<returnvalue>numeric</returnvalue>
</para>
<para>
Truncates <parameter>v</parameter> to <parameter>s</parameter>
decimal places
</para>
<para>
<literal>trunc(42.4382, 2)</literal>
<returnvalue>42.43</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>width_bucket</primary>
</indexterm>
<function>width_bucket</function> ( <parameter>operand</parameter> <type>numeric</type>, <parameter>low</parameter> <type>numeric</type>, <parameter>high</parameter> <type>numeric</type>, <parameter>count</parameter> <type>integer</type> )
<returnvalue>integer</returnvalue>
</para>
<para role="func_signature">
<function>width_bucket</function> ( <parameter>operand</parameter> <type>double precision</type>, <parameter>low</parameter> <type>double precision</type>, <parameter>high</parameter> <type>double precision</type>, <parameter>count</parameter> <type>integer</type> )
<returnvalue>integer</returnvalue>
</para>
<para>
Returns the number of the bucket in
which <parameter>operand</parameter> falls in a histogram
having <parameter>count</parameter> equal-width buckets spanning the
range <parameter>low</parameter> to <parameter>high</parameter>.
Returns <literal>0</literal>
or <literal><parameter>count</parameter>+1</literal> for an input
outside that range.
</para>
<para>
<literal>width_bucket(5.35, 0.024, 10.06, 5)</literal>
<returnvalue>3</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<function>width_bucket</function> ( <parameter>operand</parameter> <type>anycompatible</type>, <parameter>thresholds</parameter> <type>anycompatiblearray</type> )
<returnvalue>integer</returnvalue>
</para>
<para>
Returns the number of the bucket in
which <parameter>operand</parameter> falls given an array listing the
lower bounds of the buckets. Returns <literal>0</literal> for an
input less than the first lower
bound. <parameter>operand</parameter> and the array elements can be
of any type having standard comparison operators.
The <parameter>thresholds</parameter> array <emphasis>must be
sorted</emphasis>, smallest first, or unexpected results will be
obtained.
</para>
<para>
<literal>width_bucket(now(), array['yesterday', 'today', 'tomorrow']::timestamptz[])</literal>
<returnvalue>2</returnvalue>
</para></entry>
</row>
</tbody>
</tgroup>
</table>
<para>
<xref linkend="functions-math-random-table"/> shows functions for
generating random numbers.
</para>
<table id="functions-math-random-table">
<title>Random Functions</title>
<tgroup cols="1">
<thead>
<row>
<entry role="func_table_entry"><para role="func_signature">
Function
</para>
<para>
Description
</para>
<para>
Example(s)
</para></entry>
</row>
</thead>
<tbody>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>random</primary>
</indexterm>
<function>random</function> ( )
<returnvalue>double precision</returnvalue>
</para>
<para>
Returns a random value in the range 0.0 <= x < 1.0
</para>
<para>
<literal>random()</literal>
<returnvalue>0.897124072839091</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>setseed</primary>
</indexterm>
<function>setseed</function> ( <type>double precision</type> )
<returnvalue>void</returnvalue>
</para>
<para>
Sets the seed for subsequent <literal>random()</literal> calls;
argument must be between -1.0 and 1.0, inclusive
</para>
<para>
<literal>setseed(0.12345)</literal>
</para></entry>
</row>
</tbody>
</tgroup>
</table>
<para>
The <function>random()</function> function uses a simple linear
congruential algorithm. It is fast but not suitable for cryptographic
applications; see the <xref linkend="pgcrypto"/> module for a more
secure alternative.
If <function>setseed()</function> is called, the series of results of
subsequent <function>random()</function> calls in the current session
can be repeated by re-issuing <function>setseed()</function> with the same
argument.
</para>
<para>
<xref linkend="functions-math-trig-table"/> shows the
available trigonometric functions. Each of these functions comes in
two variants, one that measures angles in radians and one that
measures angles in degrees.
</para>
<table id="functions-math-trig-table">
<title>Trigonometric Functions</title>
<tgroup cols="1">
<thead>
<row>
<entry role="func_table_entry"><para role="func_signature">
Function
</para>
<para>
Description
</para>
<para>
Example(s)
</para></entry>
</row>
</thead>
<tbody>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>acos</primary>
</indexterm>
<function>acos</function> ( <type>double precision</type> )
<returnvalue>double precision</returnvalue>
</para>
<para>
Inverse cosine, result in radians
</para>
<para>
<literal>acos(1)</literal>
<returnvalue>0</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>acosd</primary>
</indexterm>
<function>acosd</function> ( <type>double precision</type> )
<returnvalue>double precision</returnvalue>
</para>
<para>
Inverse cosine, result in degrees
</para>
<para>
<literal>acosd(0.5)</literal>
<returnvalue>60</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>asin</primary>
</indexterm>
<function>asin</function> ( <type>double precision</type> )
<returnvalue>double precision</returnvalue>
</para>
<para>
Inverse sine, result in radians
</para>
<para>
<literal>asin(1)</literal>
<returnvalue>1.5707963267948966</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>asind</primary>
</indexterm>
<function>asind</function> ( <type>double precision</type> )
<returnvalue>double precision</returnvalue>
</para>
<para>
Inverse sine, result in degrees
</para>
<para>
<literal>asind(0.5)</literal>
<returnvalue>30</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>atan</primary>
</indexterm>
<function>atan</function> ( <type>double precision</type> )
<returnvalue>double precision</returnvalue>
</para>
<para>
Inverse tangent, result in radians
</para>
<para>
<literal>atan(1)</literal>
<returnvalue>0.7853981633974483</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>atand</primary>
</indexterm>
<function>atand</function> ( <type>double precision</type> )
<returnvalue>double precision</returnvalue>
</para>
<para>
Inverse tangent, result in degrees
</para>
<para>
<literal>atand(1)</literal>
<returnvalue>45</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>atan2</primary>
</indexterm>
<function>atan2</function> ( <parameter>y</parameter> <type>double precision</type>,
<parameter>x</parameter> <type>double precision</type> )
<returnvalue>double precision</returnvalue>
</para>
<para>
Inverse tangent of
<parameter>y</parameter>/<parameter>x</parameter>,
result in radians
</para>
<para>
<literal>atan2(1, 0)</literal>
<returnvalue>1.5707963267948966</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>atan2d</primary>
</indexterm>
<function>atan2d</function> ( <parameter>y</parameter> <type>double precision</type>,
<parameter>x</parameter> <type>double precision</type> )
<returnvalue>double precision</returnvalue>
</para>
<para>
Inverse tangent of
<parameter>y</parameter>/<parameter>x</parameter>,
result in degrees
</para>
<para>
<literal>atan2d(1, 0)</literal>
<returnvalue>90</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>cos</primary>
</indexterm>
<function>cos</function> ( <type>double precision</type> )
<returnvalue>double precision</returnvalue>
</para>
<para>
Cosine, argument in radians
</para>
<para>
<literal>cos(0)</literal>
<returnvalue>1</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>cosd</primary>
</indexterm>
<function>cosd</function> ( <type>double precision</type> )
<returnvalue>double precision</returnvalue>
</para>
<para>
Cosine, argument in degrees
</para>
<para>
<literal>cosd(60)</literal>
<returnvalue>0.5</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>cot</primary>
</indexterm>
<function>cot</function> ( <type>double precision</type> )
<returnvalue>double precision</returnvalue>
</para>
<para>
Cotangent, argument in radians
</para>
<para>
<literal>cot(0.5)</literal>
<returnvalue>1.830487721712452</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>cotd</primary>
</indexterm>
<function>cotd</function> ( <type>double precision</type> )
<returnvalue>double precision</returnvalue>
</para>
<para>
Cotangent, argument in degrees
</para>
<para>
<literal>cotd(45)</literal>
<returnvalue>1</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>sin</primary>
</indexterm>
<function>sin</function> ( <type>double precision</type> )
<returnvalue>double precision</returnvalue>
</para>
<para>
Sine, argument in radians
</para>
<para>
<literal>sin(1)</literal>
<returnvalue>0.8414709848078965</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>sind</primary>
</indexterm>
<function>sind</function> ( <type>double precision</type> )
<returnvalue>double precision</returnvalue>
</para>
<para>
Sine, argument in degrees
</para>
<para>
<literal>sind(30)</literal>
<returnvalue>0.5</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>tan</primary>
</indexterm>
<function>tan</function> ( <type>double precision</type> )
<returnvalue>double precision</returnvalue>
</para>
<para>
Tangent, argument in radians
</para>
<para>
<literal>tan(1)</literal>
<returnvalue>1.5574077246549023</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>tand</primary>
</indexterm>
<function>tand</function> ( <type>double precision</type> )
<returnvalue>double precision</returnvalue>
</para>
<para>
Tangent, argument in degrees
</para>
<para>
<literal>tand(45)</literal>
<returnvalue>1</returnvalue>
</para></entry>
</row>
</tbody>
</tgroup>
</table>
<note>
<para>
Another way to work with angles measured in degrees is to use the unit
transformation functions <literal><function>radians()</function></literal>
and <literal><function>degrees()</function></literal> shown earlier.
However, using the degree-based trigonometric functions is preferred,
as that way avoids round-off error for special cases such
as <literal>sind(30)</literal>.
</para>
</note>
<para>
<xref linkend="functions-math-hyp-table"/> shows the
available hyperbolic functions.
</para>
<table id="functions-math-hyp-table">
<title>Hyperbolic Functions</title>
<tgroup cols="1">
<thead>
<row>
<entry role="func_table_entry"><para role="func_signature">
Function
</para>
<para>
Description
</para>
<para>
Example(s)
</para></entry>
</row>
</thead>
<tbody>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>sinh</primary>
</indexterm>
<function>sinh</function> ( <type>double precision</type> )
<returnvalue>double precision</returnvalue>
</para>
<para>
Hyperbolic sine
</para>
<para>
<literal>sinh(1)</literal>
<returnvalue>1.1752011936438014</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>cosh</primary>
</indexterm>
<function>cosh</function> ( <type>double precision</type> )
<returnvalue>double precision</returnvalue>
</para>
<para>
Hyperbolic cosine
</para>
<para>
<literal>cosh(0)</literal>
<returnvalue>1</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>tanh</primary>
</indexterm>
<function>tanh</function> ( <type>double precision</type> )
<returnvalue>double precision</returnvalue>
</para>
<para>
Hyperbolic tangent
</para>
<para>
<literal>tanh(1)</literal>
<returnvalue>0.7615941559557649</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>asinh</primary>
</indexterm>
<function>asinh</function> ( <type>double precision</type> )
<returnvalue>double precision</returnvalue>
</para>
<para>
Inverse hyperbolic sine
</para>
<para>
<literal>asinh(1)</literal>
<returnvalue>0.881373587019543</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>acosh</primary>
</indexterm>
<function>acosh</function> ( <type>double precision</type> )
<returnvalue>double precision</returnvalue>
</para>
<para>
Inverse hyperbolic cosine
</para>
<para>
<literal>acosh(1)</literal>
<returnvalue>0</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>atanh</primary>
</indexterm>
<function>atanh</function> ( <type>double precision</type> )
<returnvalue>double precision</returnvalue>
</para>
<para>
Inverse hyperbolic tangent
</para>
<para>
<literal>atanh(0.5)</literal>
<returnvalue>0.5493061443340548</returnvalue>
</para></entry>
</row>
</tbody>
</tgroup>
</table>
</sect1>
<sect1 id="functions-string">
<title>String Functions and Operators</title>
<para>
This section describes functions and operators for examining and
manipulating string values. Strings in this context include values
of the types <type>character</type>, <type>character varying</type>,
and <type>text</type>. Except where noted, these functions and operators
are declared to accept and return type <type>text</type>. They will
interchangeably accept <type>character varying</type> arguments.
Values of type <type>character</type> will be converted
to <type>text</type> before the function or operator is applied, resulting
in stripping any trailing spaces in the <type>character</type> value.
</para>
<para>
<acronym>SQL</acronym> defines some string functions that use
key words, rather than commas, to separate
arguments. Details are in
<xref linkend="functions-string-sql"/>.
<productname>PostgreSQL</productname> also provides versions of these functions
that use the regular function invocation syntax
(see <xref linkend="functions-string-other"/>).
</para>
<note>
<para>
The string concatenation operator (<literal>||</literal>) will accept
non-string input, so long as at least one input is of string type, as shown
in <xref linkend="functions-string-sql"/>. For other cases, inserting an
explicit coercion to <type>text</type> can be used to have non-string input
accepted.
</para>
</note>
<table id="functions-string-sql">
<title><acronym>SQL</acronym> String Functions and Operators</title>
<tgroup cols="1">
<thead>
<row>
<entry role="func_table_entry"><para role="func_signature">
Function/Operator
</para>
<para>
Description
</para>
<para>
Example(s)
</para></entry>
</row>
</thead>
<tbody>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>character string</primary>
<secondary>concatenation</secondary>
</indexterm>
<type>text</type> <literal>||</literal> <type>text</type>
<returnvalue>text</returnvalue>
</para>
<para>
Concatenates the two strings.
</para>
<para>
<literal>'Post' || 'greSQL'</literal>
<returnvalue>PostgreSQL</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<type>text</type> <literal>||</literal> <type>anynonarray</type>
<returnvalue>text</returnvalue>
</para>
<para role="func_signature">
<type>anynonarray</type> <literal>||</literal> <type>text</type>
<returnvalue>text</returnvalue>
</para>
<para>
Converts the non-string input to text, then concatenates the two
strings. (The non-string input cannot be of an array type, because
that would create ambiguity with the array <literal>||</literal>
operators. If you want to concatenate an array's text equivalent,
cast it to <type>text</type> explicitly.)
</para>
<para>
<literal>'Value: ' || 42</literal>
<returnvalue>Value: 42</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>normalized</primary>
</indexterm>
<indexterm>
<primary>Unicode normalization</primary>
</indexterm>
<type>text</type> <literal>IS</literal> <optional><literal>NOT</literal></optional> <optional><parameter>form</parameter></optional> <literal>NORMALIZED</literal>
<returnvalue>boolean</returnvalue>
</para>
<para>
Checks whether the string is in the specified Unicode normalization
form. The optional <parameter>form</parameter> key word specifies the
form: <literal>NFC</literal> (the default), <literal>NFD</literal>,
<literal>NFKC</literal>, or <literal>NFKD</literal>. This expression can
only be used when the server encoding is <literal>UTF8</literal>. Note
that checking for normalization using this expression is often faster
than normalizing possibly already normalized strings.
</para>
<para>
<literal>U&'\0061\0308bc' IS NFD NORMALIZED</literal>
<returnvalue>t</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>bit_length</primary>
</indexterm>
<function>bit_length</function> ( <type>text</type> )
<returnvalue>integer</returnvalue>
</para>
<para>
Returns number of bits in the string (8
times the <function>octet_length</function>).
</para>
<para>
<literal>bit_length('jose')</literal>
<returnvalue>32</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>char_length</primary>
</indexterm>
<indexterm>
<primary>character string</primary>
<secondary>length</secondary>
</indexterm>
<indexterm>
<primary>length</primary>
<secondary sortas="character string">of a character string</secondary>
<see>character string, length</see>
</indexterm>
<function>char_length</function> ( <type>text</type> )
<returnvalue>integer</returnvalue>
</para>
<para role="func_signature">
<indexterm>
<primary>character_length</primary>
</indexterm>
<function>character_length</function> ( <type>text</type> )
<returnvalue>integer</returnvalue>
</para>
<para>
Returns number of characters in the string.
</para>
<para>
<literal>char_length('josé')</literal>
<returnvalue>4</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>lower</primary>
</indexterm>
<function>lower</function> ( <type>text</type> )
<returnvalue>text</returnvalue>
</para>
<para>
Converts the string to all lower case, according to the rules of the
database's locale.
</para>
<para>
<literal>lower('TOM')</literal>
<returnvalue>tom</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>normalize</primary>
</indexterm>
<indexterm>
<primary>Unicode normalization</primary>
</indexterm>
<function>normalize</function> ( <type>text</type>
<optional>, <parameter>form</parameter> </optional> )
<returnvalue>text</returnvalue>
</para>
<para>
Converts the string to the specified Unicode
normalization form. The optional <parameter>form</parameter> key word
specifies the form: <literal>NFC</literal> (the default),
<literal>NFD</literal>, <literal>NFKC</literal>, or
<literal>NFKD</literal>. This function can only be used when the
server encoding is <literal>UTF8</literal>.
</para>
<para>
<literal>normalize(U&'\0061\0308bc', NFC)</literal>
<returnvalue>U&'\00E4bc'</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>octet_length</primary>
</indexterm>
<function>octet_length</function> ( <type>text</type> )
<returnvalue>integer</returnvalue>
</para>
<para>
Returns number of bytes in the string.
</para>
<para>
<literal>octet_length('josé')</literal>
<returnvalue>5</returnvalue> (if server encoding is UTF8)
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>octet_length</primary>
</indexterm>
<function>octet_length</function> ( <type>character</type> )
<returnvalue>integer</returnvalue>
</para>
<para>
Returns number of bytes in the string. Since this version of the
function accepts type <type>character</type> directly, it will not
strip trailing spaces.
</para>
<para>
<literal>octet_length('abc '::character(4))</literal>
<returnvalue>4</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>overlay</primary>
</indexterm>
<function>overlay</function> ( <parameter>string</parameter> <type>text</type> <literal>PLACING</literal> <parameter>newsubstring</parameter> <type>text</type> <literal>FROM</literal> <parameter>start</parameter> <type>integer</type> <optional> <literal>FOR</literal> <parameter>count</parameter> <type>integer</type> </optional> )
<returnvalue>text</returnvalue>
</para>
<para>
Replaces the substring of <parameter>string</parameter> that starts at
the <parameter>start</parameter>'th character and extends
for <parameter>count</parameter> characters
with <parameter>newsubstring</parameter>.
If <parameter>count</parameter> is omitted, it defaults to the length
of <parameter>newsubstring</parameter>.
</para>
<para>
<literal>overlay('Txxxxas' placing 'hom' from 2 for 4)</literal>
<returnvalue>Thomas</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>position</primary>
</indexterm>
<function>position</function> ( <parameter>substring</parameter> <type>text</type> <literal>IN</literal> <parameter>string</parameter> <type>text</type> )
<returnvalue>integer</returnvalue>
</para>
<para>
Returns first starting index of the specified
<parameter>substring</parameter> within
<parameter>string</parameter>, or zero if it's not present.
</para>
<para>
<literal>position('om' in 'Thomas')</literal>
<returnvalue>3</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>substring</primary>
</indexterm>
<function>substring</function> ( <parameter>string</parameter> <type>text</type> <optional> <literal>FROM</literal> <parameter>start</parameter> <type>integer</type> </optional> <optional> <literal>FOR</literal> <parameter>count</parameter> <type>integer</type> </optional> )
<returnvalue>text</returnvalue>
</para>
<para>
Extracts the substring of <parameter>string</parameter> starting at
the <parameter>start</parameter>'th character if that is specified,
and stopping after <parameter>count</parameter> characters if that is
specified. Provide at least one of <parameter>start</parameter>
and <parameter>count</parameter>.
</para>
<para>
<literal>substring('Thomas' from 2 for 3)</literal>
<returnvalue>hom</returnvalue>
</para>
<para>
<literal>substring('Thomas' from 3)</literal>
<returnvalue>omas</returnvalue>
</para>
<para>
<literal>substring('Thomas' for 2)</literal>
<returnvalue>Th</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<function>substring</function> ( <parameter>string</parameter> <type>text</type> <literal>FROM</literal> <parameter>pattern</parameter> <type>text</type> )
<returnvalue>text</returnvalue>
</para>
<para>
Extracts the first substring matching POSIX regular expression; see
<xref linkend="functions-posix-regexp"/>.
</para>
<para>
<literal>substring('Thomas' from '...$')</literal>
<returnvalue>mas</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<function>substring</function> ( <parameter>string</parameter> <type>text</type> <literal>SIMILAR</literal> <parameter>pattern</parameter> <type>text</type> <literal>ESCAPE</literal> <parameter>escape</parameter> <type>text</type> )
<returnvalue>text</returnvalue>
</para>
<para role="func_signature">
<function>substring</function> ( <parameter>string</parameter> <type>text</type> <literal>FROM</literal> <parameter>pattern</parameter> <type>text</type> <literal>FOR</literal> <parameter>escape</parameter> <type>text</type> )
<returnvalue>text</returnvalue>
</para>
<para>
Extracts the first substring matching <acronym>SQL</acronym> regular expression;
see <xref linkend="functions-similarto-regexp"/>. The first form has
been specified since SQL:2003; the second form was only in SQL:1999
and should be considered obsolete.
</para>
<para>
<literal>substring('Thomas' similar '%#"o_a#"_' escape '#')</literal>
<returnvalue>oma</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>trim</primary>
</indexterm>
<function>trim</function> ( <optional> <literal>LEADING</literal> | <literal>TRAILING</literal> | <literal>BOTH</literal> </optional>
<optional> <parameter>characters</parameter> <type>text</type> </optional> <literal>FROM</literal>
<parameter>string</parameter> <type>text</type> )
<returnvalue>text</returnvalue>
</para>
<para>
Removes the longest string containing only characters in
<parameter>characters</parameter> (a space by default) from the
start, end, or both ends (<literal>BOTH</literal> is the default)
of <parameter>string</parameter>.
</para>
<para>
<literal>trim(both 'xyz' from 'yxTomxx')</literal>
<returnvalue>Tom</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<function>trim</function> ( <optional> <literal>LEADING</literal> | <literal>TRAILING</literal> | <literal>BOTH</literal> </optional> <optional> <literal>FROM</literal> </optional>
<parameter>string</parameter> <type>text</type> <optional>,
<parameter>characters</parameter> <type>text</type> </optional> )
<returnvalue>text</returnvalue>
</para>
<para>
This is a non-standard syntax for <function>trim()</function>.
</para>
<para>
<literal>trim(both from 'yxTomxx', 'xyz')</literal>
<returnvalue>Tom</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>upper</primary>
</indexterm>
<function>upper</function> ( <type>text</type> )
<returnvalue>text</returnvalue>
</para>
<para>
Converts the string to all upper case, according to the rules of the
database's locale.
</para>
<para>
<literal>upper('tom')</literal>
<returnvalue>TOM</returnvalue>
</para></entry>
</row>
</tbody>
</tgroup>
</table>
<para>
Additional string manipulation functions are available and are
listed in <xref linkend="functions-string-other"/>. Some of them are used internally to implement the
<acronym>SQL</acronym>-standard string functions listed in <xref linkend="functions-string-sql"/>.
</para>
<table id="functions-string-other">
<title>Other String Functions</title>
<tgroup cols="1">
<thead>
<row>
<entry role="func_table_entry"><para role="func_signature">
Function
</para>
<para>
Description
</para>
<para>
Example(s)
</para></entry>
</row>
</thead>
<tbody>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>ascii</primary>
</indexterm>
<function>ascii</function> ( <type>text</type> )
<returnvalue>integer</returnvalue>
</para>
<para>
Returns the numeric code of the first character of the argument.
In <acronym>UTF8</acronym> encoding, returns the Unicode code point
of the character. In other multibyte encodings, the argument must
be an <acronym>ASCII</acronym> character.
</para>
<para>
<literal>ascii('x')</literal>
<returnvalue>120</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>btrim</primary>
</indexterm>
<function>btrim</function> ( <parameter>string</parameter> <type>text</type>
<optional>, <parameter>characters</parameter> <type>text</type> </optional> )
<returnvalue>text</returnvalue>
</para>
<para>
Removes the longest string containing only characters
in <parameter>characters</parameter> (a space by default)
from the start and end of <parameter>string</parameter>.
</para>
<para>
<literal>btrim('xyxtrimyyx', 'xyz')</literal>
<returnvalue>trim</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>chr</primary>
</indexterm>
<function>chr</function> ( <type>integer</type> )
<returnvalue>text</returnvalue>
</para>
<para>
Returns the character with the given code. In <acronym>UTF8</acronym>
encoding the argument is treated as a Unicode code point. In other
multibyte encodings the argument must designate
an <acronym>ASCII</acronym> character. <literal>chr(0)</literal> is
disallowed because text data types cannot store that character.
</para>
<para>
<literal>chr(65)</literal>
<returnvalue>A</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>concat</primary>
</indexterm>
<function>concat</function> ( <parameter>val1</parameter> <type>"any"</type>
[, <parameter>val2</parameter> <type>"any"</type> [, ...] ] )
<returnvalue>text</returnvalue>
</para>
<para>
Concatenates the text representations of all the arguments.
NULL arguments are ignored.
</para>
<para>
<literal>concat('abcde', 2, NULL, 22)</literal>
<returnvalue>abcde222</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>concat_ws</primary>
</indexterm>
<function>concat_ws</function> ( <parameter>sep</parameter> <type>text</type>,
<parameter>val1</parameter> <type>"any"</type>
[, <parameter>val2</parameter> <type>"any"</type> [, ...] ] )
<returnvalue>text</returnvalue>
</para>
<para>
Concatenates all but the first argument, with separators. The first
argument is used as the separator string, and should not be NULL.
Other NULL arguments are ignored.
</para>
<para>
<literal>concat_ws(',', 'abcde', 2, NULL, 22)</literal>
<returnvalue>abcde,2,22</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>format</primary>
</indexterm>
<function>format</function> ( <parameter>formatstr</parameter> <type>text</type>
[, <parameter>formatarg</parameter> <type>"any"</type> [, ...] ] )
<returnvalue>text</returnvalue>
</para>
<para>
Formats arguments according to a format string;
see <xref linkend="functions-string-format"/>.
This function is similar to the C function <function>sprintf</function>.
</para>
<para>
<literal>format('Hello %s, %1$s', 'World')</literal>
<returnvalue>Hello World, World</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>initcap</primary>
</indexterm>
<function>initcap</function> ( <type>text</type> )
<returnvalue>text</returnvalue>
</para>
<para>
Converts the first letter of each word to upper case and the
rest to lower case. Words are sequences of alphanumeric
characters separated by non-alphanumeric characters.
</para>
<para>
<literal>initcap('hi THOMAS')</literal>
<returnvalue>Hi Thomas</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>left</primary>
</indexterm>
<function>left</function> ( <parameter>string</parameter> <type>text</type>,
<parameter>n</parameter> <type>integer</type> )
<returnvalue>text</returnvalue>
</para>
<para>
Returns first <parameter>n</parameter> characters in the
string, or when <parameter>n</parameter> is negative, returns
all but last |<parameter>n</parameter>| characters.
</para>
<para>
<literal>left('abcde', 2)</literal>
<returnvalue>ab</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>length</primary>
</indexterm>
<function>length</function> ( <type>text</type> )
<returnvalue>integer</returnvalue>
</para>
<para>
Returns the number of characters in the string.
</para>
<para>
<literal>length('jose')</literal>
<returnvalue>4</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>lpad</primary>
</indexterm>
<function>lpad</function> ( <parameter>string</parameter> <type>text</type>,
<parameter>length</parameter> <type>integer</type>
<optional>, <parameter>fill</parameter> <type>text</type> </optional> )
<returnvalue>text</returnvalue>
</para>
<para>
Extends the <parameter>string</parameter> to length
<parameter>length</parameter> by prepending the characters
<parameter>fill</parameter> (a space by default). If the
<parameter>string</parameter> is already longer than
<parameter>length</parameter> then it is truncated (on the right).
</para>
<para>
<literal>lpad('hi', 5, 'xy')</literal>
<returnvalue>xyxhi</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>ltrim</primary>
</indexterm>
<function>ltrim</function> ( <parameter>string</parameter> <type>text</type>
<optional>, <parameter>characters</parameter> <type>text</type> </optional> )
<returnvalue>text</returnvalue>
</para>
<para>
Removes the longest string containing only characters in
<parameter>characters</parameter> (a space by default) from the start of
<parameter>string</parameter>.
</para>
<para>
<literal>ltrim('zzzytest', 'xyz')</literal>
<returnvalue>test</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>md5</primary>
</indexterm>
<function>md5</function> ( <type>text</type> )
<returnvalue>text</returnvalue>
</para>
<para>
Computes the MD5 <link linkend="functions-hash-note">hash</link> of
the argument, with the result written in hexadecimal.
</para>
<para>
<literal>md5('abc')</literal>
<returnvalue>900150983cd24fb0&zwsp;d6963f7d28e17f72</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>parse_ident</primary>
</indexterm>
<function>parse_ident</function> ( <parameter>qualified_identifier</parameter> <type>text</type>
[, <parameter>strict_mode</parameter> <type>boolean</type> <literal>DEFAULT</literal> <literal>true</literal> ] )
<returnvalue>text[]</returnvalue>
</para>
<para>
Splits <parameter>qualified_identifier</parameter> into an array of
identifiers, removing any quoting of individual identifiers. By
default, extra characters after the last identifier are considered an
error; but if the second parameter is <literal>false</literal>, then such
extra characters are ignored. (This behavior is useful for parsing
names for objects like functions.) Note that this function does not
truncate over-length identifiers. If you want truncation you can cast
the result to <type>name[]</type>.
</para>
<para>
<literal>parse_ident('"SomeSchema".someTable')</literal>
<returnvalue>{SomeSchema,sometable}</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_client_encoding</primary>
</indexterm>
<function>pg_client_encoding</function> ( )
<returnvalue>name</returnvalue>
</para>
<para>
Returns current client encoding name.
</para>
<para>
<literal>pg_client_encoding()</literal>
<returnvalue>UTF8</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>quote_ident</primary>
</indexterm>
<function>quote_ident</function> ( <type>text</type> )
<returnvalue>text</returnvalue>
</para>
<para>
Returns the given string suitably quoted to be used as an identifier
in an <acronym>SQL</acronym> statement string.
Quotes are added only if necessary (i.e., if the string contains
non-identifier characters or would be case-folded).
Embedded quotes are properly doubled.
See also <xref linkend="plpgsql-quote-literal-example"/>.
</para>
<para>
<literal>quote_ident('Foo bar')</literal>
<returnvalue>"Foo bar"</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>quote_literal</primary>
</indexterm>
<function>quote_literal</function> ( <type>text</type> )
<returnvalue>text</returnvalue>
</para>
<para>
Returns the given string suitably quoted to be used as a string literal
in an <acronym>SQL</acronym> statement string.
Embedded single-quotes and backslashes are properly doubled.
Note that <function>quote_literal</function> returns null on null
input; if the argument might be null,
<function>quote_nullable</function> is often more suitable.
See also <xref linkend="plpgsql-quote-literal-example"/>.
</para>
<para>
<literal>quote_literal(E'O\'Reilly')</literal>
<returnvalue>'O''Reilly'</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<function>quote_literal</function> ( <type>anyelement</type> )
<returnvalue>text</returnvalue>
</para>
<para>
Converts the given value to text and then quotes it as a literal.
Embedded single-quotes and backslashes are properly doubled.
</para>
<para>
<literal>quote_literal(42.5)</literal>
<returnvalue>'42.5'</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>quote_nullable</primary>
</indexterm>
<function>quote_nullable</function> ( <type>text</type> )
<returnvalue>text</returnvalue>
</para>
<para>
Returns the given string suitably quoted to be used as a string literal
in an <acronym>SQL</acronym> statement string; or, if the argument
is null, returns <literal>NULL</literal>.
Embedded single-quotes and backslashes are properly doubled.
See also <xref linkend="plpgsql-quote-literal-example"/>.
</para>
<para>
<literal>quote_nullable(NULL)</literal>
<returnvalue>NULL</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<function>quote_nullable</function> ( <type>anyelement</type> )
<returnvalue>text</returnvalue>
</para>
<para>
Converts the given value to text and then quotes it as a literal;
or, if the argument is null, returns <literal>NULL</literal>.
Embedded single-quotes and backslashes are properly doubled.
</para>
<para>
<literal>quote_nullable(42.5)</literal>
<returnvalue>'42.5'</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>regexp_match</primary>
</indexterm>
<function>regexp_match</function> ( <parameter>string</parameter> <type>text</type>, <parameter>pattern</parameter> <type>text</type> [, <parameter>flags</parameter> <type>text</type> ] )
<returnvalue>text[]</returnvalue>
</para>
<para>
Returns captured substrings resulting from the first match of a POSIX
regular expression to the <parameter>string</parameter>; see
<xref linkend="functions-posix-regexp"/>.
</para>
<para>
<literal>regexp_match('foobarbequebaz', '(bar)(beque)')</literal>
<returnvalue>{bar,beque}</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>regexp_matches</primary>
</indexterm>
<function>regexp_matches</function> ( <parameter>string</parameter> <type>text</type>, <parameter>pattern</parameter> <type>text</type> [, <parameter>flags</parameter> <type>text</type> ] )
<returnvalue>setof text[]</returnvalue>
</para>
<para>
Returns captured substrings resulting from the first match of a
POSIX regular expression to the <parameter>string</parameter>,
or multiple matches if the <literal>g</literal> flag is used;
see <xref linkend="functions-posix-regexp"/>.
</para>
<para>
<literal>regexp_matches('foobarbequebaz', 'ba.', 'g')</literal>
<returnvalue></returnvalue>
<programlisting>
{bar}
{baz}
</programlisting>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>regexp_replace</primary>
</indexterm>
<function>regexp_replace</function> ( <parameter>string</parameter> <type>text</type>, <parameter>pattern</parameter> <type>text</type>, <parameter>replacement</parameter> <type>text</type> [, <parameter>flags</parameter> <type>text</type> ] )
<returnvalue>text</returnvalue>
</para>
<para>
Replaces substrings resulting from the first match of a
POSIX regular expression, or multiple substring matches
if the <literal>g</literal> flag is used; see <xref
linkend="functions-posix-regexp"/>.
</para>
<para>
<literal>regexp_replace('Thomas', '.[mN]a.', 'M')</literal>
<returnvalue>ThM</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>regexp_split_to_array</primary>
</indexterm>
<function>regexp_split_to_array</function> ( <parameter>string</parameter> <type>text</type>, <parameter>pattern</parameter> <type>text</type> [, <parameter>flags</parameter> <type>text</type> ] )
<returnvalue>text[]</returnvalue>
</para>
<para>
Splits <parameter>string</parameter> using a POSIX regular
expression as the delimiter, producing an array of results; see
<xref linkend="functions-posix-regexp"/>.
</para>
<para>
<literal>regexp_split_to_array('hello world', '\s+')</literal>
<returnvalue>{hello,world}</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>regexp_split_to_table</primary>
</indexterm>
<function>regexp_split_to_table</function> ( <parameter>string</parameter> <type>text</type>, <parameter>pattern</parameter> <type>text</type> [, <parameter>flags</parameter> <type>text</type> ] )
<returnvalue>setof text</returnvalue>
</para>
<para>
Splits <parameter>string</parameter> using a POSIX regular
expression as the delimiter, producing a set of results; see
<xref linkend="functions-posix-regexp"/>.
</para>
<para>
<literal>regexp_split_to_table('hello world', '\s+')</literal>
<returnvalue></returnvalue>
<programlisting>
hello
world
</programlisting>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>repeat</primary>
</indexterm>
<function>repeat</function> ( <parameter>string</parameter> <type>text</type>, <parameter>number</parameter> <type>integer</type> )
<returnvalue>text</returnvalue>
</para>
<para>
Repeats <parameter>string</parameter> the specified
<parameter>number</parameter> of times.
</para>
<para>
<literal>repeat('Pg', 4)</literal>
<returnvalue>PgPgPgPg</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>replace</primary>
</indexterm>
<function>replace</function> ( <parameter>string</parameter> <type>text</type>,
<parameter>from</parameter> <type>text</type>,
<parameter>to</parameter> <type>text</type> )
<returnvalue>text</returnvalue>
</para>
<para>
Replaces all occurrences in <parameter>string</parameter> of
substring <parameter>from</parameter> with
substring <parameter>to</parameter>.
</para>
<para>
<literal>replace('abcdefabcdef', 'cd', 'XX')</literal>
<returnvalue>abXXefabXXef</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>reverse</primary>
</indexterm>
<function>reverse</function> ( <type>text</type> )
<returnvalue>text</returnvalue>
</para>
<para>
Reverses the order of the characters in the string.
</para>
<para>
<literal>reverse('abcde')</literal>
<returnvalue>edcba</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>right</primary>
</indexterm>
<function>right</function> ( <parameter>string</parameter> <type>text</type>,
<parameter>n</parameter> <type>integer</type> )
<returnvalue>text</returnvalue>
</para>
<para>
Returns last <parameter>n</parameter> characters in the string,
or when <parameter>n</parameter> is negative, returns all but
first |<parameter>n</parameter>| characters.
</para>
<para>
<literal>right('abcde', 2)</literal>
<returnvalue>de</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>rpad</primary>
</indexterm>
<function>rpad</function> ( <parameter>string</parameter> <type>text</type>,
<parameter>length</parameter> <type>integer</type>
<optional>, <parameter>fill</parameter> <type>text</type> </optional> )
<returnvalue>text</returnvalue>
</para>
<para>
Extends the <parameter>string</parameter> to length
<parameter>length</parameter> by appending the characters
<parameter>fill</parameter> (a space by default). If the
<parameter>string</parameter> is already longer than
<parameter>length</parameter> then it is truncated.
</para>
<para>
<literal>rpad('hi', 5, 'xy')</literal>
<returnvalue>hixyx</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>rtrim</primary>
</indexterm>
<function>rtrim</function> ( <parameter>string</parameter> <type>text</type>
<optional>, <parameter>characters</parameter> <type>text</type> </optional> )
<returnvalue>text</returnvalue>
</para>
<para>
Removes the longest string containing only characters in
<parameter>characters</parameter> (a space by default) from the end of
<parameter>string</parameter>.
</para>
<para>
<literal>rtrim('testxxzx', 'xyz')</literal>
<returnvalue>test</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>split_part</primary>
</indexterm>
<function>split_part</function> ( <parameter>string</parameter> <type>text</type>,
<parameter>delimiter</parameter> <type>text</type>,
<parameter>n</parameter> <type>integer</type> )
<returnvalue>text</returnvalue>
</para>
<para>
Splits <parameter>string</parameter> at occurrences
of <parameter>delimiter</parameter> and returns
the <parameter>n</parameter>'th field (counting from one),
or when <parameter>n</parameter> is negative, returns
the |<parameter>n</parameter>|'th-from-last field.
</para>
<para>
<literal>split_part('abc~@~def~@~ghi', '~@~', 2)</literal>
<returnvalue>def</returnvalue>
</para>
<para>
<literal>split_part('abc,def,ghi,jkl', ',', -2)</literal>
<returnvalue>ghi</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>strpos</primary>
</indexterm>
<function>strpos</function> ( <parameter>string</parameter> <type>text</type>, <parameter>substring</parameter> <type>text</type> )
<returnvalue>integer</returnvalue>
</para>
<para>
Returns first starting index of the specified <parameter>substring</parameter>
within <parameter>string</parameter>, or zero if it's not present.
(Same as <literal>position(<parameter>substring</parameter> in
<parameter>string</parameter>)</literal>, but note the reversed
argument order.)
</para>
<para>
<literal>strpos('high', 'ig')</literal>
<returnvalue>2</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>substr</primary>
</indexterm>
<function>substr</function> ( <parameter>string</parameter> <type>text</type>, <parameter>start</parameter> <type>integer</type> <optional>, <parameter>count</parameter> <type>integer</type> </optional> )
<returnvalue>text</returnvalue>
</para>
<para>
Extracts the substring of <parameter>string</parameter> starting at
the <parameter>start</parameter>'th character,
and extending for <parameter>count</parameter> characters if that is
specified. (Same
as <literal>substring(<parameter>string</parameter>
from <parameter>start</parameter>
for <parameter>count</parameter>)</literal>.)
</para>
<para>
<literal>substr('alphabet', 3)</literal>
<returnvalue>phabet</returnvalue>
</para>
<para>
<literal>substr('alphabet', 3, 2)</literal>
<returnvalue>ph</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>starts_with</primary>
</indexterm>
<function>starts_with</function> ( <parameter>string</parameter> <type>text</type>, <parameter>prefix</parameter> <type>text</type> )
<returnvalue>boolean</returnvalue>
</para>
<para>
Returns true if <parameter>string</parameter> starts
with <parameter>prefix</parameter>.
</para>
<para>
<literal>starts_with('alphabet', 'alph')</literal>
<returnvalue>t</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>string_to_array</primary>
</indexterm>
<function>string_to_array</function> ( <parameter>string</parameter> <type>text</type>, <parameter>delimiter</parameter> <type>text</type> <optional>, <parameter>null_string</parameter> <type>text</type> </optional> )
<returnvalue>text[]</returnvalue>
</para>
<para>
Splits the <parameter>string</parameter> at occurrences
of <parameter>delimiter</parameter> and forms the resulting fields
into a <type>text</type> array.
If <parameter>delimiter</parameter> is <literal>NULL</literal>,
each character in the <parameter>string</parameter> will become a
separate element in the array.
If <parameter>delimiter</parameter> is an empty string, then
the <parameter>string</parameter> is treated as a single field.
If <parameter>null_string</parameter> is supplied and is
not <literal>NULL</literal>, fields matching that string are
replaced by <literal>NULL</literal>.
</para>
<para>
<literal>string_to_array('xx~~yy~~zz', '~~', 'yy')</literal>
<returnvalue>{xx,NULL,zz}</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>string_to_table</primary>
</indexterm>
<function>string_to_table</function> ( <parameter>string</parameter> <type>text</type>, <parameter>delimiter</parameter> <type>text</type> <optional>, <parameter>null_string</parameter> <type>text</type> </optional> )
<returnvalue>setof text</returnvalue>
</para>
<para>
Splits the <parameter>string</parameter> at occurrences
of <parameter>delimiter</parameter> and returns the resulting fields
as a set of <type>text</type> rows.
If <parameter>delimiter</parameter> is <literal>NULL</literal>,
each character in the <parameter>string</parameter> will become a
separate row of the result.
If <parameter>delimiter</parameter> is an empty string, then
the <parameter>string</parameter> is treated as a single field.
If <parameter>null_string</parameter> is supplied and is
not <literal>NULL</literal>, fields matching that string are
replaced by <literal>NULL</literal>.
</para>
<para>
<literal>string_to_table('xx~^~yy~^~zz', '~^~', 'yy')</literal>
<returnvalue></returnvalue>
<programlisting>
xx
NULL
zz
</programlisting>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>to_ascii</primary>
</indexterm>
<function>to_ascii</function> ( <parameter>string</parameter> <type>text</type> )
<returnvalue>text</returnvalue>
</para>
<para role="func_signature">
<function>to_ascii</function> ( <parameter>string</parameter> <type>text</type>,
<parameter>encoding</parameter> <type>name</type> )
<returnvalue>text</returnvalue>
</para>
<para role="func_signature">
<function>to_ascii</function> ( <parameter>string</parameter> <type>text</type>,
<parameter>encoding</parameter> <type>integer</type> )
<returnvalue>text</returnvalue>
</para>
<para>
Converts <parameter>string</parameter> to <acronym>ASCII</acronym>
from another encoding, which may be identified by name or number.
If <parameter>encoding</parameter> is omitted the database encoding
is assumed (which in practice is the only useful case).
The conversion consists primarily of dropping accents.
Conversion is only supported
from <literal>LATIN1</literal>, <literal>LATIN2</literal>,
<literal>LATIN9</literal>, and <literal>WIN1250</literal> encodings.
(See the <xref linkend="unaccent"/> module for another, more flexible
solution.)
</para>
<para>
<literal>to_ascii('Karél')</literal>
<returnvalue>Karel</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>to_hex</primary>
</indexterm>
<function>to_hex</function> ( <type>integer</type> )
<returnvalue>text</returnvalue>
</para>
<para role="func_signature">
<function>to_hex</function> ( <type>bigint</type> )
<returnvalue>text</returnvalue>
</para>
<para>
Converts the number to its equivalent hexadecimal representation.
</para>
<para>
<literal>to_hex(2147483647)</literal>
<returnvalue>7fffffff</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>translate</primary>
</indexterm>
<function>translate</function> ( <parameter>string</parameter> <type>text</type>,
<parameter>from</parameter> <type>text</type>,
<parameter>to</parameter> <type>text</type> )
<returnvalue>text</returnvalue>
</para>
<para>
Replaces each character in <parameter>string</parameter> that
matches a character in the <parameter>from</parameter> set with the
corresponding character in the <parameter>to</parameter>
set. If <parameter>from</parameter> is longer than
<parameter>to</parameter>, occurrences of the extra characters in
<parameter>from</parameter> are deleted.
</para>
<para>
<literal>translate('12345', '143', 'ax')</literal>
<returnvalue>a2x5</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>unistr</primary>
</indexterm>
<function>unistr</function> ( <type>text</type> )
<returnvalue>text</returnvalue>
</para>
<para>
Evaluate escaped Unicode characters in the argument. Unicode characters
can be specified as
<literal>\<replaceable>XXXX</replaceable></literal> (4 hexadecimal
digits), <literal>\+<replaceable>XXXXXX</replaceable></literal> (6
hexadecimal digits),
<literal>\u<replaceable>XXXX</replaceable></literal> (4 hexadecimal
digits), or <literal>\U<replaceable>XXXXXXXX</replaceable></literal>
(8 hexadecimal digits). To specify a backslash, write two
backslashes. All other characters are taken literally.
</para>
<para>
If the server encoding is not UTF-8, the Unicode code point identified
by one of these escape sequences is converted to the actual server
encoding; an error is reported if that's not possible.
</para>
<para>
This function provides a (non-standard) alternative to string
constants with Unicode escapes (see <xref
linkend="sql-syntax-strings-uescape"/>).
</para>
<para>
<literal>unistr('d\0061t\+000061')</literal>
<returnvalue>data</returnvalue>
</para>
<para>
<literal>unistr('d\u0061t\U00000061')</literal>
<returnvalue>data</returnvalue>
</para></entry>
</row>
</tbody>
</tgroup>
</table>
<para>
The <function>concat</function>, <function>concat_ws</function> and
<function>format</function> functions are variadic, so it is possible to
pass the values to be concatenated or formatted as an array marked with
the <literal>VARIADIC</literal> keyword (see <xref
linkend="xfunc-sql-variadic-functions"/>). The array's elements are
treated as if they were separate ordinary arguments to the function.
If the variadic array argument is NULL, <function>concat</function>
and <function>concat_ws</function> return NULL, but
<function>format</function> treats a NULL as a zero-element array.
</para>
<para>
See also the aggregate function <function>string_agg</function> in
<xref linkend="functions-aggregate"/>, and the functions for
converting between strings and the <type>bytea</type> type in
<xref linkend="functions-binarystring-conversions"/>.
</para>
<sect2 id="functions-string-format">
<title><function>format</function></title>
<indexterm>
<primary>format</primary>
</indexterm>
<para>
The function <function>format</function> produces output formatted according to
a format string, in a style similar to the C function
<function>sprintf</function>.
</para>
<para>
<synopsis>
<function>format</function>(<parameter>formatstr</parameter> <type>text</type> [, <parameter>formatarg</parameter> <type>"any"</type> [, ...] ])
</synopsis>
<parameter>formatstr</parameter> is a format string that specifies how the
result should be formatted. Text in the format string is copied
directly to the result, except where <firstterm>format specifiers</firstterm> are
used. Format specifiers act as placeholders in the string, defining how
subsequent function arguments should be formatted and inserted into the
result. Each <parameter>formatarg</parameter> argument is converted to text
according to the usual output rules for its data type, and then formatted
and inserted into the result string according to the format specifier(s).
</para>
<para>
Format specifiers are introduced by a <literal>%</literal> character and have
the form
<synopsis>
%[<parameter>position</parameter>][<parameter>flags</parameter>][<parameter>width</parameter>]<parameter>type</parameter>
</synopsis>
where the component fields are:
<variablelist>
<varlistentry>
<term><parameter>position</parameter> (optional)</term>
<listitem>
<para>
A string of the form <literal><parameter>n</parameter>$</literal> where
<parameter>n</parameter> is the index of the argument to print.
Index 1 means the first argument after
<parameter>formatstr</parameter>. If the <parameter>position</parameter> is
omitted, the default is to use the next argument in sequence.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><parameter>flags</parameter> (optional)</term>
<listitem>
<para>
Additional options controlling how the format specifier's output is
formatted. Currently the only supported flag is a minus sign
(<literal>-</literal>) which will cause the format specifier's output to be
left-justified. This has no effect unless the <parameter>width</parameter>
field is also specified.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><parameter>width</parameter> (optional)</term>
<listitem>
<para>
Specifies the <emphasis>minimum</emphasis> number of characters to use to
display the format specifier's output. The output is padded on the
left or right (depending on the <literal>-</literal> flag) with spaces as
needed to fill the width. A too-small width does not cause
truncation of the output, but is simply ignored. The width may be
specified using any of the following: a positive integer; an
asterisk (<literal>*</literal>) to use the next function argument as the
width; or a string of the form <literal>*<parameter>n</parameter>$</literal> to
use the <parameter>n</parameter>th function argument as the width.
</para>
<para>
If the width comes from a function argument, that argument is
consumed before the argument that is used for the format specifier's
value. If the width argument is negative, the result is left
aligned (as if the <literal>-</literal> flag had been specified) within a
field of length <function>abs</function>(<parameter>width</parameter>).
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><parameter>type</parameter> (required)</term>
<listitem>
<para>
The type of format conversion to use to produce the format
specifier's output. The following types are supported:
<itemizedlist>
<listitem>
<para>
<literal>s</literal> formats the argument value as a simple
string. A null value is treated as an empty string.
</para>
</listitem>
<listitem>
<para>
<literal>I</literal> treats the argument value as an SQL
identifier, double-quoting it if necessary.
It is an error for the value to be null (equivalent to
<function>quote_ident</function>).
</para>
</listitem>
<listitem>
<para>
<literal>L</literal> quotes the argument value as an SQL literal.
A null value is displayed as the string <literal>NULL</literal>, without
quotes (equivalent to <function>quote_nullable</function>).
</para>
</listitem>
</itemizedlist>
</para>
</listitem>
</varlistentry>
</variablelist>
</para>
<para>
In addition to the format specifiers described above, the special sequence
<literal>%%</literal> may be used to output a literal <literal>%</literal> character.
</para>
<para>
Here are some examples of the basic format conversions:
<screen>
SELECT format('Hello %s', 'World');
<lineannotation>Result: </lineannotation><computeroutput>Hello World</computeroutput>
SELECT format('Testing %s, %s, %s, %%', 'one', 'two', 'three');
<lineannotation>Result: </lineannotation><computeroutput>Testing one, two, three, %</computeroutput>
SELECT format('INSERT INTO %I VALUES(%L)', 'Foo bar', E'O\'Reilly');
<lineannotation>Result: </lineannotation><computeroutput>INSERT INTO "Foo bar" VALUES('O''Reilly')</computeroutput>
SELECT format('INSERT INTO %I VALUES(%L)', 'locations', 'C:\Program Files');
<lineannotation>Result: </lineannotation><computeroutput>INSERT INTO locations VALUES('C:\Program Files')</computeroutput>
</screen>
</para>
<para>
Here are examples using <parameter>width</parameter> fields
and the <literal>-</literal> flag:
<screen>
SELECT format('|%10s|', 'foo');
<lineannotation>Result: </lineannotation><computeroutput>| foo|</computeroutput>
SELECT format('|%-10s|', 'foo');
<lineannotation>Result: </lineannotation><computeroutput>|foo |</computeroutput>
SELECT format('|%*s|', 10, 'foo');
<lineannotation>Result: </lineannotation><computeroutput>| foo|</computeroutput>
SELECT format('|%*s|', -10, 'foo');
<lineannotation>Result: </lineannotation><computeroutput>|foo |</computeroutput>
SELECT format('|%-*s|', 10, 'foo');
<lineannotation>Result: </lineannotation><computeroutput>|foo |</computeroutput>
SELECT format('|%-*s|', -10, 'foo');
<lineannotation>Result: </lineannotation><computeroutput>|foo |</computeroutput>
</screen>
</para>
<para>
These examples show use of <parameter>position</parameter> fields:
<screen>
SELECT format('Testing %3$s, %2$s, %1$s', 'one', 'two', 'three');
<lineannotation>Result: </lineannotation><computeroutput>Testing three, two, one</computeroutput>
SELECT format('|%*2$s|', 'foo', 10, 'bar');
<lineannotation>Result: </lineannotation><computeroutput>| bar|</computeroutput>
SELECT format('|%1$*2$s|', 'foo', 10, 'bar');
<lineannotation>Result: </lineannotation><computeroutput>| foo|</computeroutput>
</screen>
</para>
<para>
Unlike the standard C function <function>sprintf</function>,
<productname>PostgreSQL</productname>'s <function>format</function> function allows format
specifiers with and without <parameter>position</parameter> fields to be mixed
in the same format string. A format specifier without a
<parameter>position</parameter> field always uses the next argument after the
last argument consumed.
In addition, the <function>format</function> function does not require all
function arguments to be used in the format string.
For example:
<screen>
SELECT format('Testing %3$s, %2$s, %s', 'one', 'two', 'three');
<lineannotation>Result: </lineannotation><computeroutput>Testing three, two, three</computeroutput>
</screen>
</para>
<para>
The <literal>%I</literal> and <literal>%L</literal> format specifiers are particularly
useful for safely constructing dynamic SQL statements. See
<xref linkend="plpgsql-quote-literal-example"/>.
</para>
</sect2>
</sect1>
<sect1 id="functions-binarystring">
<title>Binary String Functions and Operators</title>
<indexterm zone="functions-binarystring">
<primary>binary data</primary>
<secondary>functions</secondary>
</indexterm>
<para>
This section describes functions and operators for examining and
manipulating binary strings, that is values of type <type>bytea</type>.
Many of these are equivalent, in purpose and syntax, to the
text-string functions described in the previous section.
</para>
<para>
<acronym>SQL</acronym> defines some string functions that use
key words, rather than commas, to separate
arguments. Details are in
<xref linkend="functions-binarystring-sql"/>.
<productname>PostgreSQL</productname> also provides versions of these functions
that use the regular function invocation syntax
(see <xref linkend="functions-binarystring-other"/>).
</para>
<table id="functions-binarystring-sql">
<title><acronym>SQL</acronym> Binary String Functions and Operators</title>
<tgroup cols="1">
<thead>
<row>
<entry role="func_table_entry"><para role="func_signature">
Function/Operator
</para>
<para>
Description
</para>
<para>
Example(s)
</para></entry>
</row>
</thead>
<tbody>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>binary string</primary>
<secondary>concatenation</secondary>
</indexterm>
<type>bytea</type> <literal>||</literal> <type>bytea</type>
<returnvalue>bytea</returnvalue>
</para>
<para>
Concatenates the two binary strings.
</para>
<para>
<literal>'\x123456'::bytea || '\x789a00bcde'::bytea</literal>
<returnvalue>\x123456789a00bcde</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>bit_length</primary>
</indexterm>
<function>bit_length</function> ( <type>bytea</type> )
<returnvalue>integer</returnvalue>
</para>
<para>
Returns number of bits in the binary string (8
times the <function>octet_length</function>).
</para>
<para>
<literal>bit_length('\x123456'::bytea)</literal>
<returnvalue>24</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>octet_length</primary>
</indexterm>
<function>octet_length</function> ( <type>bytea</type> )
<returnvalue>integer</returnvalue>
</para>
<para>
Returns number of bytes in the binary string.
</para>
<para>
<literal>octet_length('\x123456'::bytea)</literal>
<returnvalue>3</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>overlay</primary>
</indexterm>
<function>overlay</function> ( <parameter>bytes</parameter> <type>bytea</type> <literal>PLACING</literal> <parameter>newsubstring</parameter> <type>bytea</type> <literal>FROM</literal> <parameter>start</parameter> <type>integer</type> <optional> <literal>FOR</literal> <parameter>count</parameter> <type>integer</type> </optional> )
<returnvalue>bytea</returnvalue>
</para>
<para>
Replaces the substring of <parameter>bytes</parameter> that starts at
the <parameter>start</parameter>'th byte and extends
for <parameter>count</parameter> bytes
with <parameter>newsubstring</parameter>.
If <parameter>count</parameter> is omitted, it defaults to the length
of <parameter>newsubstring</parameter>.
</para>
<para>
<literal>overlay('\x1234567890'::bytea placing '\002\003'::bytea from 2 for 3)</literal>
<returnvalue>\x12020390</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>position</primary>
</indexterm>
<function>position</function> ( <parameter>substring</parameter> <type>bytea</type> <literal>IN</literal> <parameter>bytes</parameter> <type>bytea</type> )
<returnvalue>integer</returnvalue>
</para>
<para>
Returns first starting index of the specified
<parameter>substring</parameter> within
<parameter>bytes</parameter>, or zero if it's not present.
</para>
<para>
<literal>position('\x5678'::bytea in '\x1234567890'::bytea)</literal>
<returnvalue>3</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>substring</primary>
</indexterm>
<function>substring</function> ( <parameter>bytes</parameter> <type>bytea</type> <optional> <literal>FROM</literal> <parameter>start</parameter> <type>integer</type> </optional> <optional> <literal>FOR</literal> <parameter>count</parameter> <type>integer</type> </optional> )
<returnvalue>bytea</returnvalue>
</para>
<para>
Extracts the substring of <parameter>bytes</parameter> starting at
the <parameter>start</parameter>'th byte if that is specified,
and stopping after <parameter>count</parameter> bytes if that is
specified. Provide at least one of <parameter>start</parameter>
and <parameter>count</parameter>.
</para>
<para>
<literal>substring('\x1234567890'::bytea from 3 for 2)</literal>
<returnvalue>\x5678</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>trim</primary>
</indexterm>
<function>trim</function> ( <optional> <literal>LEADING</literal> | <literal>TRAILING</literal> | <literal>BOTH</literal> </optional>
<parameter>bytesremoved</parameter> <type>bytea</type> <literal>FROM</literal>
<parameter>bytes</parameter> <type>bytea</type> )
<returnvalue>bytea</returnvalue>
</para>
<para>
Removes the longest string containing only bytes appearing in
<parameter>bytesremoved</parameter> from the start,
end, or both ends (<literal>BOTH</literal> is the default)
of <parameter>bytes</parameter>.
</para>
<para>
<literal>trim('\x9012'::bytea from '\x1234567890'::bytea)</literal>
<returnvalue>\x345678</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<function>trim</function> ( <optional> <literal>LEADING</literal> | <literal>TRAILING</literal> | <literal>BOTH</literal> </optional> <optional> <literal>FROM</literal> </optional>
<parameter>bytes</parameter> <type>bytea</type>,
<parameter>bytesremoved</parameter> <type>bytea</type> )
<returnvalue>bytea</returnvalue>
</para>
<para>
This is a non-standard syntax for <function>trim()</function>.
</para>
<para>
<literal>trim(both from '\x1234567890'::bytea, '\x9012'::bytea)</literal>
<returnvalue>\x345678</returnvalue>
</para></entry>
</row>
</tbody>
</tgroup>
</table>
<para>
Additional binary string manipulation functions are available and
are listed in <xref linkend="functions-binarystring-other"/>. Some
of them are used internally to implement the
<acronym>SQL</acronym>-standard string functions listed in <xref
linkend="functions-binarystring-sql"/>.
</para>
<table id="functions-binarystring-other">
<title>Other Binary String Functions</title>
<tgroup cols="1">
<thead>
<row>
<entry role="func_table_entry"><para role="func_signature">
Function
</para>
<para>
Description
</para>
<para>
Example(s)
</para></entry>
</row>
</thead>
<tbody>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>bit_count</primary>
</indexterm>
<indexterm>
<primary>popcount</primary>
<see>bit_count</see>
</indexterm>
<function>bit_count</function> ( <parameter>bytes</parameter> <type>bytea</type> )
<returnvalue>bigint</returnvalue>
</para>
<para>
Returns the number of bits set in the binary string (also known as
<quote>popcount</quote>).
</para>
<para>
<literal>bit_count('\x1234567890'::bytea)</literal>
<returnvalue>31</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>btrim</primary>
</indexterm>
<function>btrim</function> ( <parameter>bytes</parameter> <type>bytea</type>,
<parameter>bytesremoved</parameter> <type>bytea</type> )
<returnvalue>bytea</returnvalue>
</para>
<para>
Removes the longest string containing only bytes appearing in
<parameter>bytesremoved</parameter> from the start and end of
<parameter>bytes</parameter>.
</para>
<para>
<literal>btrim('\x1234567890'::bytea, '\x9012'::bytea)</literal>
<returnvalue>\x345678</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>get_bit</primary>
</indexterm>
<function>get_bit</function> ( <parameter>bytes</parameter> <type>bytea</type>,
<parameter>n</parameter> <type>bigint</type> )
<returnvalue>integer</returnvalue>
</para>
<para>
Extracts <link linkend="functions-zerobased-note">n'th</link> bit
from binary string.
</para>
<para>
<literal>get_bit('\x1234567890'::bytea, 30)</literal>
<returnvalue>1</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>get_byte</primary>
</indexterm>
<function>get_byte</function> ( <parameter>bytes</parameter> <type>bytea</type>,
<parameter>n</parameter> <type>integer</type> )
<returnvalue>integer</returnvalue>
</para>
<para>
Extracts <link linkend="functions-zerobased-note">n'th</link> byte
from binary string.
</para>
<para>
<literal>get_byte('\x1234567890'::bytea, 4)</literal>
<returnvalue>144</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>length</primary>
</indexterm>
<indexterm>
<primary>binary string</primary>
<secondary>length</secondary>
</indexterm>
<indexterm>
<primary>length</primary>
<secondary sortas="binary string">of a binary string</secondary>
<see>binary strings, length</see>
</indexterm>
<function>length</function> ( <type>bytea</type> )
<returnvalue>integer</returnvalue>
</para>
<para>
Returns the number of bytes in the binary string.
</para>
<para>
<literal>length('\x1234567890'::bytea)</literal>
<returnvalue>5</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<function>length</function> ( <parameter>bytes</parameter> <type>bytea</type>,
<parameter>encoding</parameter> <type>name</type> )
<returnvalue>integer</returnvalue>
</para>
<para>
Returns the number of characters in the binary string, assuming
that it is text in the given <parameter>encoding</parameter>.
</para>
<para>
<literal>length('jose'::bytea, 'UTF8')</literal>
<returnvalue>4</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>ltrim</primary>
</indexterm>
<function>ltrim</function> ( <parameter>bytes</parameter> <type>bytea</type>,
<parameter>bytesremoved</parameter> <type>bytea</type> )
<returnvalue>bytea</returnvalue>
</para>
<para>
Removes the longest string containing only bytes appearing in
<parameter>bytesremoved</parameter> from the start of
<parameter>bytes</parameter>.
</para>
<para>
<literal>ltrim('\x1234567890'::bytea, '\x9012'::bytea)</literal>
<returnvalue>\x34567890</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>md5</primary>
</indexterm>
<function>md5</function> ( <type>bytea</type> )
<returnvalue>text</returnvalue>
</para>
<para>
Computes the MD5 <link linkend="functions-hash-note">hash</link> of
the binary string, with the result written in hexadecimal.
</para>
<para>
<literal>md5('Th\000omas'::bytea)</literal>
<returnvalue>8ab2d3c9689aaf18&zwsp;b4958c334c82d8b1</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>rtrim</primary>
</indexterm>
<function>rtrim</function> ( <parameter>bytes</parameter> <type>bytea</type>,
<parameter>bytesremoved</parameter> <type>bytea</type> )
<returnvalue>bytea</returnvalue>
</para>
<para>
Removes the longest string containing only bytes appearing in
<parameter>bytesremoved</parameter> from the end of
<parameter>bytes</parameter>.
</para>
<para>
<literal>rtrim('\x1234567890'::bytea, '\x9012'::bytea)</literal>
<returnvalue>\x12345678</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>set_bit</primary>
</indexterm>
<function>set_bit</function> ( <parameter>bytes</parameter> <type>bytea</type>,
<parameter>n</parameter> <type>bigint</type>,
<parameter>newvalue</parameter> <type>integer</type> )
<returnvalue>bytea</returnvalue>
</para>
<para>
Sets <link linkend="functions-zerobased-note">n'th</link> bit in
binary string to <parameter>newvalue</parameter>.
</para>
<para>
<literal>set_bit('\x1234567890'::bytea, 30, 0)</literal>
<returnvalue>\x1234563890</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>set_byte</primary>
</indexterm>
<function>set_byte</function> ( <parameter>bytes</parameter> <type>bytea</type>,
<parameter>n</parameter> <type>integer</type>,
<parameter>newvalue</parameter> <type>integer</type> )
<returnvalue>bytea</returnvalue>
</para>
<para>
Sets <link linkend="functions-zerobased-note">n'th</link> byte in
binary string to <parameter>newvalue</parameter>.
</para>
<para>
<literal>set_byte('\x1234567890'::bytea, 4, 64)</literal>
<returnvalue>\x1234567840</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>sha224</primary>
</indexterm>
<function>sha224</function> ( <type>bytea</type> )
<returnvalue>bytea</returnvalue>
</para>
<para>
Computes the SHA-224 <link linkend="functions-hash-note">hash</link>
of the binary string.
</para>
<para>
<literal>sha224('abc'::bytea)</literal>
<returnvalue>\x23097d223405d8228642a477bda2&zwsp;55b32aadbce4bda0b3f7e36c9da7</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>sha256</primary>
</indexterm>
<function>sha256</function> ( <type>bytea</type> )
<returnvalue>bytea</returnvalue>
</para>
<para>
Computes the SHA-256 <link linkend="functions-hash-note">hash</link>
of the binary string.
</para>
<para>
<literal>sha256('abc'::bytea)</literal>
<returnvalue>\xba7816bf8f01cfea414140de5dae2223&zwsp;b00361a396177a9cb410ff61f20015ad</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>sha384</primary>
</indexterm>
<function>sha384</function> ( <type>bytea</type> )
<returnvalue>bytea</returnvalue>
</para>
<para>
Computes the SHA-384 <link linkend="functions-hash-note">hash</link>
of the binary string.
</para>
<para>
<literal>sha384('abc'::bytea)</literal>
<returnvalue>\xcb00753f45a35e8bb5a03d699ac65007&zwsp;272c32ab0eded1631a8b605a43ff5bed&zwsp;8086072ba1e7cc2358baeca134c825a7</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>sha512</primary>
</indexterm>
<function>sha512</function> ( <type>bytea</type> )
<returnvalue>bytea</returnvalue>
</para>
<para>
Computes the SHA-512 <link linkend="functions-hash-note">hash</link>
of the binary string.
</para>
<para>
<literal>sha512('abc'::bytea)</literal>
<returnvalue>\xddaf35a193617abacc417349ae204131&zwsp;12e6fa4e89a97ea20a9eeee64b55d39a&zwsp;2192992a274fc1a836ba3c23a3feebbd&zwsp;454d4423643ce80e2a9ac94fa54ca49f</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>substr</primary>
</indexterm>
<function>substr</function> ( <parameter>bytes</parameter> <type>bytea</type>, <parameter>start</parameter> <type>integer</type> <optional>, <parameter>count</parameter> <type>integer</type> </optional> )
<returnvalue>bytea</returnvalue>
</para>
<para>
Extracts the substring of <parameter>bytes</parameter> starting at
the <parameter>start</parameter>'th byte,
and extending for <parameter>count</parameter> bytes if that is
specified. (Same
as <literal>substring(<parameter>bytes</parameter>
from <parameter>start</parameter>
for <parameter>count</parameter>)</literal>.)
</para>
<para>
<literal>substr('\x1234567890'::bytea, 3, 2)</literal>
<returnvalue>\x5678</returnvalue>
</para></entry>
</row>
</tbody>
</tgroup>
</table>
<para id="functions-zerobased-note">
Functions <function>get_byte</function> and <function>set_byte</function>
number the first byte of a binary string as byte 0.
Functions <function>get_bit</function> and <function>set_bit</function>
number bits from the right within each byte; for example bit 0 is the least
significant bit of the first byte, and bit 15 is the most significant bit
of the second byte.
</para>
<para id="functions-hash-note">
For historical reasons, the function <function>md5</function>
returns a hex-encoded value of type <type>text</type> whereas the SHA-2
functions return type <type>bytea</type>. Use the functions
<link linkend="function-encode"><function>encode</function></link>
and <link linkend="function-decode"><function>decode</function></link> to
convert between the two. For example write <literal>encode(sha256('abc'),
'hex')</literal> to get a hex-encoded text representation,
or <literal>decode(md5('abc'), 'hex')</literal> to get
a <type>bytea</type> value.
</para>
<para>
<indexterm>
<primary>character string</primary>
<secondary>converting to binary string</secondary>
</indexterm>
<indexterm>
<primary>binary string</primary>
<secondary>converting to character string</secondary>
</indexterm>
Functions for converting strings between different character sets
(encodings), and for representing arbitrary binary data in textual
form, are shown in
<xref linkend="functions-binarystring-conversions"/>. For these
functions, an argument or result of type <type>text</type> is expressed
in the database's default encoding, while arguments or results of
type <type>bytea</type> are in an encoding named by another argument.
</para>
<table id="functions-binarystring-conversions">
<title>Text/Binary String Conversion Functions</title>
<tgroup cols="1">
<thead>
<row>
<entry role="func_table_entry"><para role="func_signature">
Function
</para>
<para>
Description
</para>
<para>
Example(s)
</para></entry>
</row>
</thead>
<tbody>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>convert</primary>
</indexterm>
<function>convert</function> ( <parameter>bytes</parameter> <type>bytea</type>,
<parameter>src_encoding</parameter> <type>name</type>,
<parameter>dest_encoding</parameter> <type>name</type> )
<returnvalue>bytea</returnvalue>
</para>
<para>
Converts a binary string representing text in
encoding <parameter>src_encoding</parameter>
to a binary string in encoding <parameter>dest_encoding</parameter>
(see <xref linkend="multibyte-conversions-supported"/> for
available conversions).
</para>
<para>
<literal>convert('text_in_utf8', 'UTF8', 'LATIN1')</literal>
<returnvalue>\x746578745f696e5f75746638</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>convert_from</primary>
</indexterm>
<function>convert_from</function> ( <parameter>bytes</parameter> <type>bytea</type>,
<parameter>src_encoding</parameter> <type>name</type> )
<returnvalue>text</returnvalue>
</para>
<para>
Converts a binary string representing text in
encoding <parameter>src_encoding</parameter>
to <type>text</type> in the database encoding
(see <xref linkend="multibyte-conversions-supported"/> for
available conversions).
</para>
<para>
<literal>convert_from('text_in_utf8', 'UTF8')</literal>
<returnvalue>text_in_utf8</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>convert_to</primary>
</indexterm>
<function>convert_to</function> ( <parameter>string</parameter> <type>text</type>,
<parameter>dest_encoding</parameter> <type>name</type> )
<returnvalue>bytea</returnvalue>
</para>
<para>
Converts a <type>text</type> string (in the database encoding) to a
binary string encoded in encoding <parameter>dest_encoding</parameter>
(see <xref linkend="multibyte-conversions-supported"/> for
available conversions).
</para>
<para>
<literal>convert_to('some_text', 'UTF8')</literal>
<returnvalue>\x736f6d655f74657874</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm id="function-encode">
<primary>encode</primary>
</indexterm>
<function>encode</function> ( <parameter>bytes</parameter> <type>bytea</type>,
<parameter>format</parameter> <type>text</type> )
<returnvalue>text</returnvalue>
</para>
<para>
Encodes binary data into a textual representation; supported
<parameter>format</parameter> values are:
<link linkend="encode-format-base64"><literal>base64</literal></link>,
<link linkend="encode-format-escape"><literal>escape</literal></link>,
<link linkend="encode-format-hex"><literal>hex</literal></link>.
</para>
<para>
<literal>encode('123\000\001', 'base64')</literal>
<returnvalue>MTIzAAE=</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm id="function-decode">
<primary>decode</primary>
</indexterm>
<function>decode</function> ( <parameter>string</parameter> <type>text</type>,
<parameter>format</parameter> <type>text</type> )
<returnvalue>bytea</returnvalue>
</para>
<para>
Decodes binary data from a textual representation; supported
<parameter>format</parameter> values are the same as
for <function>encode</function>.
</para>
<para>
<literal>decode('MTIzAAE=', 'base64')</literal>
<returnvalue>\x3132330001</returnvalue>
</para></entry>
</row>
</tbody>
</tgroup>
</table>
<para>
The <function>encode</function> and <function>decode</function>
functions support the following textual formats:
<variablelist>
<varlistentry id="encode-format-base64">
<term>base64
<indexterm>
<primary>base64 format</primary>
</indexterm></term>
<listitem>
<para>
The <literal>base64</literal> format is that
of <ulink url="https://tools.ietf.org/html/rfc2045#section-6.8">RFC
2045 Section 6.8</ulink>. As per the <acronym>RFC</acronym>, encoded lines are
broken at 76 characters. However instead of the MIME CRLF
end-of-line marker, only a newline is used for end-of-line.
The <function>decode</function> function ignores carriage-return,
newline, space, and tab characters. Otherwise, an error is
raised when <function>decode</function> is supplied invalid
base64 data — including when trailing padding is incorrect.
</para>
</listitem>
</varlistentry>
<varlistentry id="encode-format-escape">
<term>escape
<indexterm>
<primary>escape format</primary>
</indexterm></term>
<listitem>
<para>
The <literal>escape</literal> format converts zero bytes and
bytes with the high bit set into octal escape sequences
(<literal>\</literal><replaceable>nnn</replaceable>), and it doubles
backslashes. Other byte values are represented literally.
The <function>decode</function> function will raise an error if a
backslash is not followed by either a second backslash or three
octal digits; it accepts other byte values unchanged.
</para>
</listitem>
</varlistentry>
<varlistentry id="encode-format-hex">
<term>hex
<indexterm>
<primary>hex format</primary>
</indexterm></term>
<listitem>
<para>
The <literal>hex</literal> format represents each 4 bits of
data as one hexadecimal digit, <literal>0</literal>
through <literal>f</literal>, writing the higher-order digit of
each byte first. The <function>encode</function> function outputs
the <literal>a</literal>-<literal>f</literal> hex digits in lower
case. Because the smallest unit of data is 8 bits, there are
always an even number of characters returned
by <function>encode</function>.
The <function>decode</function> function
accepts the <literal>a</literal>-<literal>f</literal> characters in
either upper or lower case. An error is raised
when <function>decode</function> is given invalid hex data
— including when given an odd number of characters.
</para>
</listitem>
</varlistentry>
</variablelist>
</para>
<para>
See also the aggregate function <function>string_agg</function> in
<xref linkend="functions-aggregate"/> and the large object functions
in <xref linkend="lo-funcs"/>.
</para>
</sect1>
<sect1 id="functions-bitstring">
<title>Bit String Functions and Operators</title>
<indexterm zone="functions-bitstring">
<primary>bit strings</primary>
<secondary>functions</secondary>
</indexterm>
<para>
This section describes functions and operators for examining and
manipulating bit strings, that is values of the types
<type>bit</type> and <type>bit varying</type>. (While only
type <type>bit</type> is mentioned in these tables, values of
type <type>bit varying</type> can be used interchangeably.)
Bit strings support the usual comparison operators shown in
<xref linkend="functions-comparison-op-table"/>, as well as the
operators shown in <xref linkend="functions-bit-string-op-table"/>.
</para>
<table id="functions-bit-string-op-table">
<title>Bit String Operators</title>
<tgroup cols="1">
<thead>
<row>
<entry role="func_table_entry"><para role="func_signature">
Operator
</para>
<para>
Description
</para>
<para>
Example(s)
</para></entry>
</row>
</thead>
<tbody>
<row>
<entry role="func_table_entry"><para role="func_signature">
<type>bit</type> <literal>||</literal> <type>bit</type>
<returnvalue>bit</returnvalue>
</para>
<para>
Concatenation
</para>
<para>
<literal>B'10001' || B'011'</literal>
<returnvalue>10001011</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<type>bit</type> <literal>&</literal> <type>bit</type>
<returnvalue>bit</returnvalue>
</para>
<para>
Bitwise AND (inputs must be of equal length)
</para>
<para>
<literal>B'10001' & B'01101'</literal>
<returnvalue>00001</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<type>bit</type> <literal>|</literal> <type>bit</type>
<returnvalue>bit</returnvalue>
</para>
<para>
Bitwise OR (inputs must be of equal length)
</para>
<para>
<literal>B'10001' | B'01101'</literal>
<returnvalue>11101</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<type>bit</type> <literal>#</literal> <type>bit</type>
<returnvalue>bit</returnvalue>
</para>
<para>
Bitwise exclusive OR (inputs must be of equal length)
</para>
<para>
<literal>B'10001' # B'01101'</literal>
<returnvalue>11100</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<literal>~</literal> <type>bit</type>
<returnvalue>bit</returnvalue>
</para>
<para>
Bitwise NOT
</para>
<para>
<literal>~ B'10001'</literal>
<returnvalue>01110</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<type>bit</type> <literal><<</literal> <type>integer</type>
<returnvalue>bit</returnvalue>
</para>
<para>
Bitwise shift left
(string length is preserved)
</para>
<para>
<literal>B'10001' << 3</literal>
<returnvalue>01000</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<type>bit</type> <literal>>></literal> <type>integer</type>
<returnvalue>bit</returnvalue>
</para>
<para>
Bitwise shift right
(string length is preserved)
</para>
<para>
<literal>B'10001' >> 2</literal>
<returnvalue>00100</returnvalue>
</para></entry>
</row>
</tbody>
</tgroup>
</table>
<para>
Some of the functions available for binary strings are also available
for bit strings, as shown in <xref linkend="functions-bit-string-table"/>.
</para>
<table id="functions-bit-string-table">
<title>Bit String Functions</title>
<tgroup cols="1">
<thead>
<row>
<entry role="func_table_entry"><para role="func_signature">
Function
</para>
<para>
Description
</para>
<para>
Example(s)
</para></entry>
</row>
</thead>
<tbody>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>bit_count</primary>
</indexterm>
<function>bit_count</function> ( <type>bit</type> )
<returnvalue>bigint</returnvalue>
</para>
<para>
Returns the number of bits set in the bit string (also known as
<quote>popcount</quote>).
</para>
<para>
<literal>bit_count(B'10111')</literal>
<returnvalue>4</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>bit_length</primary>
</indexterm>
<function>bit_length</function> ( <type>bit</type> )
<returnvalue>integer</returnvalue>
</para>
<para>
Returns number of bits in the bit string.
</para>
<para>
<literal>bit_length(B'10111')</literal>
<returnvalue>5</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>length</primary>
</indexterm>
<indexterm>
<primary>bit string</primary>
<secondary>length</secondary>
</indexterm>
<function>length</function> ( <type>bit</type> )
<returnvalue>integer</returnvalue>
</para>
<para>
Returns number of bits in the bit string.
</para>
<para>
<literal>length(B'10111')</literal>
<returnvalue>5</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>octet_length</primary>
</indexterm>
<function>octet_length</function> ( <type>bit</type> )
<returnvalue>integer</returnvalue>
</para>
<para>
Returns number of bytes in the bit string.
</para>
<para>
<literal>octet_length(B'1011111011')</literal>
<returnvalue>2</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>overlay</primary>
</indexterm>
<function>overlay</function> ( <parameter>bits</parameter> <type>bit</type> <literal>PLACING</literal> <parameter>newsubstring</parameter> <type>bit</type> <literal>FROM</literal> <parameter>start</parameter> <type>integer</type> <optional> <literal>FOR</literal> <parameter>count</parameter> <type>integer</type> </optional> )
<returnvalue>bit</returnvalue>
</para>
<para>
Replaces the substring of <parameter>bits</parameter> that starts at
the <parameter>start</parameter>'th bit and extends
for <parameter>count</parameter> bits
with <parameter>newsubstring</parameter>.
If <parameter>count</parameter> is omitted, it defaults to the length
of <parameter>newsubstring</parameter>.
</para>
<para>
<literal>overlay(B'01010101010101010' placing B'11111' from 2 for 3)</literal>
<returnvalue>0111110101010101010</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>position</primary>
</indexterm>
<function>position</function> ( <parameter>substring</parameter> <type>bit</type> <literal>IN</literal> <parameter>bits</parameter> <type>bit</type> )
<returnvalue>integer</returnvalue>
</para>
<para>
Returns first starting index of the specified <parameter>substring</parameter>
within <parameter>bits</parameter>, or zero if it's not present.
</para>
<para>
<literal>position(B'010' in B'000001101011')</literal>
<returnvalue>8</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>substring</primary>
</indexterm>
<function>substring</function> ( <parameter>bits</parameter> <type>bit</type> <optional> <literal>FROM</literal> <parameter>start</parameter> <type>integer</type> </optional> <optional> <literal>FOR</literal> <parameter>count</parameter> <type>integer</type> </optional> )
<returnvalue>bit</returnvalue>
</para>
<para>
Extracts the substring of <parameter>bits</parameter> starting at
the <parameter>start</parameter>'th bit if that is specified,
and stopping after <parameter>count</parameter> bits if that is
specified. Provide at least one of <parameter>start</parameter>
and <parameter>count</parameter>.
</para>
<para>
<literal>substring(B'110010111111' from 3 for 2)</literal>
<returnvalue>00</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>get_bit</primary>
</indexterm>
<function>get_bit</function> ( <parameter>bits</parameter> <type>bit</type>,
<parameter>n</parameter> <type>integer</type> )
<returnvalue>integer</returnvalue>
</para>
<para>
Extracts <parameter>n</parameter>'th bit
from bit string; the first (leftmost) bit is bit 0.
</para>
<para>
<literal>get_bit(B'101010101010101010', 6)</literal>
<returnvalue>1</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>set_bit</primary>
</indexterm>
<function>set_bit</function> ( <parameter>bits</parameter> <type>bit</type>,
<parameter>n</parameter> <type>integer</type>,
<parameter>newvalue</parameter> <type>integer</type> )
<returnvalue>bit</returnvalue>
</para>
<para>
Sets <parameter>n</parameter>'th bit in
bit string to <parameter>newvalue</parameter>;
the first (leftmost) bit is bit 0.
</para>
<para>
<literal>set_bit(B'101010101010101010', 6, 0)</literal>
<returnvalue>101010001010101010</returnvalue>
</para></entry>
</row>
</tbody>
</tgroup>
</table>
<para>
In addition, it is possible to cast integral values to and from type
<type>bit</type>.
Casting an integer to <type>bit(n)</type> copies the rightmost
<literal>n</literal> bits. Casting an integer to a bit string width wider
than the integer itself will sign-extend on the left.
Some examples:
<programlisting>
44::bit(10) <lineannotation>0000101100</lineannotation>
44::bit(3) <lineannotation>100</lineannotation>
cast(-44 as bit(12)) <lineannotation>111111010100</lineannotation>
'1110'::bit(4)::integer <lineannotation>14</lineannotation>
</programlisting>
Note that casting to just <quote>bit</quote> means casting to
<literal>bit(1)</literal>, and so will deliver only the least significant
bit of the integer.
</para>
</sect1>
<sect1 id="functions-matching">
<title>Pattern Matching</title>
<indexterm zone="functions-matching">
<primary>pattern matching</primary>
</indexterm>
<para>
There are three separate approaches to pattern matching provided
by <productname>PostgreSQL</productname>: the traditional
<acronym>SQL</acronym> <function>LIKE</function> operator, the
more recent <function>SIMILAR TO</function> operator (added in
SQL:1999), and <acronym>POSIX</acronym>-style regular
expressions. Aside from the basic <quote>does this string match
this pattern?</quote> operators, functions are available to extract
or replace matching substrings and to split a string at matching
locations.
</para>
<tip>
<para>
If you have pattern matching needs that go beyond this,
consider writing a user-defined function in Perl or Tcl.
</para>
</tip>
<caution>
<para>
While most regular-expression searches can be executed very quickly,
regular expressions can be contrived that take arbitrary amounts of
time and memory to process. Be wary of accepting regular-expression
search patterns from hostile sources. If you must do so, it is
advisable to impose a statement timeout.
</para>
<para>
Searches using <function>SIMILAR TO</function> patterns have the same
security hazards, since <function>SIMILAR TO</function> provides many
of the same capabilities as <acronym>POSIX</acronym>-style regular
expressions.
</para>
<para>
<function>LIKE</function> searches, being much simpler than the other
two options, are safer to use with possibly-hostile pattern sources.
</para>
</caution>
<para>
The pattern matching operators of all three kinds do not support
nondeterministic collations. If required, apply a different collation to
the expression to work around this limitation.
</para>
<sect2 id="functions-like">
<title><function>LIKE</function></title>
<indexterm>
<primary>LIKE</primary>
</indexterm>
<synopsis>
<replaceable>string</replaceable> LIKE <replaceable>pattern</replaceable> <optional>ESCAPE <replaceable>escape-character</replaceable></optional>
<replaceable>string</replaceable> NOT LIKE <replaceable>pattern</replaceable> <optional>ESCAPE <replaceable>escape-character</replaceable></optional>
</synopsis>
<para>
The <function>LIKE</function> expression returns true if the
<replaceable>string</replaceable> matches the supplied
<replaceable>pattern</replaceable>. (As
expected, the <function>NOT LIKE</function> expression returns
false if <function>LIKE</function> returns true, and vice versa.
An equivalent expression is
<literal>NOT (<replaceable>string</replaceable> LIKE
<replaceable>pattern</replaceable>)</literal>.)
</para>
<para>
If <replaceable>pattern</replaceable> does not contain percent
signs or underscores, then the pattern only represents the string
itself; in that case <function>LIKE</function> acts like the
equals operator. An underscore (<literal>_</literal>) in
<replaceable>pattern</replaceable> stands for (matches) any single
character; a percent sign (<literal>%</literal>) matches any sequence
of zero or more characters.
</para>
<para>
Some examples:
<programlisting>
'abc' LIKE 'abc' <lineannotation>true</lineannotation>
'abc' LIKE 'a%' <lineannotation>true</lineannotation>
'abc' LIKE '_b_' <lineannotation>true</lineannotation>
'abc' LIKE 'c' <lineannotation>false</lineannotation>
</programlisting>
</para>
<para>
<function>LIKE</function> pattern matching always covers the entire
string. Therefore, if it's desired to match a sequence anywhere within
a string, the pattern must start and end with a percent sign.
</para>
<para>
To match a literal underscore or percent sign without matching
other characters, the respective character in
<replaceable>pattern</replaceable> must be
preceded by the escape character. The default escape
character is the backslash but a different one can be selected by
using the <literal>ESCAPE</literal> clause. To match the escape
character itself, write two escape characters.
</para>
<note>
<para>
If you have <xref linkend="guc-standard-conforming-strings"/> turned off,
any backslashes you write in literal string constants will need to be
doubled. See <xref linkend="sql-syntax-strings"/> for more information.
</para>
</note>
<para>
It's also possible to select no escape character by writing
<literal>ESCAPE ''</literal>. This effectively disables the
escape mechanism, which makes it impossible to turn off the
special meaning of underscore and percent signs in the pattern.
</para>
<para>
According to the SQL standard, omitting <literal>ESCAPE</literal>
means there is no escape character (rather than defaulting to a
backslash), and a zero-length <literal>ESCAPE</literal> value is
disallowed. <productname>PostgreSQL</productname>'s behavior in
this regard is therefore slightly nonstandard.
</para>
<para>
The key word <token>ILIKE</token> can be used instead of
<token>LIKE</token> to make the match case-insensitive according
to the active locale. This is not in the <acronym>SQL</acronym> standard but is a
<productname>PostgreSQL</productname> extension.
</para>
<para>
The operator <literal>~~</literal> is equivalent to
<function>LIKE</function>, and <literal>~~*</literal> corresponds to
<function>ILIKE</function>. There are also
<literal>!~~</literal> and <literal>!~~*</literal> operators that
represent <function>NOT LIKE</function> and <function>NOT
ILIKE</function>, respectively. All of these operators are
<productname>PostgreSQL</productname>-specific. You may see these
operator names in <command>EXPLAIN</command> output and similar
places, since the parser actually translates <function>LIKE</function>
et al. to these operators.
</para>
<para>
The phrases <function>LIKE</function>, <function>ILIKE</function>,
<function>NOT LIKE</function>, and <function>NOT ILIKE</function> are
generally treated as operators
in <productname>PostgreSQL</productname> syntax; for example they can
be used in <replaceable>expression</replaceable>
<replaceable>operator</replaceable> ANY
(<replaceable>subquery</replaceable>) constructs, although
an <literal>ESCAPE</literal> clause cannot be included there. In some
obscure cases it may be necessary to use the underlying operator names
instead.
</para>
<para>
Also see the prefix operator <literal>^@</literal> and corresponding
<function>starts_with</function> function, which are useful in cases
where simply matching the beginning of a string is needed.
</para>
</sect2>
<sect2 id="functions-similarto-regexp">
<title><function>SIMILAR TO</function> Regular Expressions</title>
<indexterm>
<primary>regular expression</primary>
<!-- <seealso>pattern matching</seealso> breaks index build -->
</indexterm>
<indexterm>
<primary>SIMILAR TO</primary>
</indexterm>
<indexterm>
<primary>substring</primary>
</indexterm>
<synopsis>
<replaceable>string</replaceable> SIMILAR TO <replaceable>pattern</replaceable> <optional>ESCAPE <replaceable>escape-character</replaceable></optional>
<replaceable>string</replaceable> NOT SIMILAR TO <replaceable>pattern</replaceable> <optional>ESCAPE <replaceable>escape-character</replaceable></optional>
</synopsis>
<para>
The <function>SIMILAR TO</function> operator returns true or
false depending on whether its pattern matches the given string.
It is similar to <function>LIKE</function>, except that it
interprets the pattern using the SQL standard's definition of a
regular expression. SQL regular expressions are a curious cross
between <function>LIKE</function> notation and common (POSIX) regular
expression notation.
</para>
<para>
Like <function>LIKE</function>, the <function>SIMILAR TO</function>
operator succeeds only if its pattern matches the entire string;
this is unlike common regular expression behavior where the pattern
can match any part of the string.
Also like
<function>LIKE</function>, <function>SIMILAR TO</function> uses
<literal>_</literal> and <literal>%</literal> as wildcard characters denoting
any single character and any string, respectively (these are
comparable to <literal>.</literal> and <literal>.*</literal> in POSIX regular
expressions).
</para>
<para>
In addition to these facilities borrowed from <function>LIKE</function>,
<function>SIMILAR TO</function> supports these pattern-matching
metacharacters borrowed from POSIX regular expressions:
<itemizedlist>
<listitem>
<para>
<literal>|</literal> denotes alternation (either of two alternatives).
</para>
</listitem>
<listitem>
<para>
<literal>*</literal> denotes repetition of the previous item zero
or more times.
</para>
</listitem>
<listitem>
<para>
<literal>+</literal> denotes repetition of the previous item one
or more times.
</para>
</listitem>
<listitem>
<para>
<literal>?</literal> denotes repetition of the previous item zero
or one time.
</para>
</listitem>
<listitem>
<para>
<literal>{</literal><replaceable>m</replaceable><literal>}</literal> denotes repetition
of the previous item exactly <replaceable>m</replaceable> times.
</para>
</listitem>
<listitem>
<para>
<literal>{</literal><replaceable>m</replaceable><literal>,}</literal> denotes repetition
of the previous item <replaceable>m</replaceable> or more times.
</para>
</listitem>
<listitem>
<para>
<literal>{</literal><replaceable>m</replaceable><literal>,</literal><replaceable>n</replaceable><literal>}</literal>
denotes repetition of the previous item at least <replaceable>m</replaceable> and
not more than <replaceable>n</replaceable> times.
</para>
</listitem>
<listitem>
<para>
Parentheses <literal>()</literal> can be used to group items into
a single logical item.
</para>
</listitem>
<listitem>
<para>
A bracket expression <literal>[...]</literal> specifies a character
class, just as in POSIX regular expressions.
</para>
</listitem>
</itemizedlist>
Notice that the period (<literal>.</literal>) is not a metacharacter
for <function>SIMILAR TO</function>.
</para>
<para>
As with <function>LIKE</function>, a backslash disables the special
meaning of any of these metacharacters. A different escape character
can be specified with <literal>ESCAPE</literal>, or the escape
capability can be disabled by writing <literal>ESCAPE ''</literal>.
</para>
<para>
According to the SQL standard, omitting <literal>ESCAPE</literal>
means there is no escape character (rather than defaulting to a
backslash), and a zero-length <literal>ESCAPE</literal> value is
disallowed. <productname>PostgreSQL</productname>'s behavior in
this regard is therefore slightly nonstandard.
</para>
<para>
Another nonstandard extension is that following the escape character
with a letter or digit provides access to the escape sequences
defined for POSIX regular expressions; see
<xref linkend="posix-character-entry-escapes-table"/>,
<xref linkend="posix-class-shorthand-escapes-table"/>, and
<xref linkend="posix-constraint-escapes-table"/> below.
</para>
<para>
Some examples:
<programlisting>
'abc' SIMILAR TO 'abc' <lineannotation>true</lineannotation>
'abc' SIMILAR TO 'a' <lineannotation>false</lineannotation>
'abc' SIMILAR TO '%(b|d)%' <lineannotation>true</lineannotation>
'abc' SIMILAR TO '(b|c)%' <lineannotation>false</lineannotation>
'-abc-' SIMILAR TO '%\mabc\M%' <lineannotation>true</lineannotation>
'xabcy' SIMILAR TO '%\mabc\M%' <lineannotation>false</lineannotation>
</programlisting>
</para>
<para>
The <function>substring</function> function with three parameters
provides extraction of a substring that matches an SQL
regular expression pattern. The function can be written according
to standard SQL syntax:
<synopsis>
substring(<replaceable>string</replaceable> similar <replaceable>pattern</replaceable> escape <replaceable>escape-character</replaceable>)
</synopsis>
or using the now obsolete SQL:1999 syntax:
<synopsis>
substring(<replaceable>string</replaceable> from <replaceable>pattern</replaceable> for <replaceable>escape-character</replaceable>)
</synopsis>
or as a plain three-argument function:
<synopsis>
substring(<replaceable>string</replaceable>, <replaceable>pattern</replaceable>, <replaceable>escape-character</replaceable>)
</synopsis>
As with <literal>SIMILAR TO</literal>, the
specified pattern must match the entire data string, or else the
function fails and returns null. To indicate the part of the
pattern for which the matching data sub-string is of interest,
the pattern should contain
two occurrences of the escape character followed by a double quote
(<literal>"</literal>). <!-- " font-lock sanity -->
The text matching the portion of the pattern
between these separators is returned when the match is successful.
</para>
<para>
The escape-double-quote separators actually
divide <function>substring</function>'s pattern into three independent
regular expressions; for example, a vertical bar (<literal>|</literal>)
in any of the three sections affects only that section. Also, the first
and third of these regular expressions are defined to match the smallest
possible amount of text, not the largest, when there is any ambiguity
about how much of the data string matches which pattern. (In POSIX
parlance, the first and third regular expressions are forced to be
non-greedy.)
</para>
<para>
As an extension to the SQL standard, <productname>PostgreSQL</productname>
allows there to be just one escape-double-quote separator, in which case
the third regular expression is taken as empty; or no separators, in which
case the first and third regular expressions are taken as empty.
</para>
<para>
Some examples, with <literal>#"</literal> delimiting the return string:
<programlisting>
substring('foobar' similar '%#"o_b#"%' escape '#') <lineannotation>oob</lineannotation>
substring('foobar' similar '#"o_b#"%' escape '#') <lineannotation>NULL</lineannotation>
</programlisting>
</para>
</sect2>
<sect2 id="functions-posix-regexp">
<title><acronym>POSIX</acronym> Regular Expressions</title>
<indexterm zone="functions-posix-regexp">
<primary>regular expression</primary>
<seealso>pattern matching</seealso>
</indexterm>
<indexterm>
<primary>substring</primary>
</indexterm>
<indexterm>
<primary>regexp_replace</primary>
</indexterm>
<indexterm>
<primary>regexp_match</primary>
</indexterm>
<indexterm>
<primary>regexp_matches</primary>
</indexterm>
<indexterm>
<primary>regexp_split_to_table</primary>
</indexterm>
<indexterm>
<primary>regexp_split_to_array</primary>
</indexterm>
<para>
<xref linkend="functions-posix-table"/> lists the available
operators for pattern matching using POSIX regular expressions.
</para>
<table id="functions-posix-table">
<title>Regular Expression Match Operators</title>
<tgroup cols="1">
<thead>
<row>
<entry role="func_table_entry"><para role="func_signature">
Operator
</para>
<para>
Description
</para>
<para>
Example(s)
</para></entry>
</row>
</thead>
<tbody>
<row>
<entry role="func_table_entry"><para role="func_signature">
<type>text</type> <literal>~</literal> <type>text</type>
<returnvalue>boolean</returnvalue>
</para>
<para>
String matches regular expression, case sensitively
</para>
<para>
<literal>'thomas' ~ 't.*ma'</literal>
<returnvalue>t</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<type>text</type> <literal>~*</literal> <type>text</type>
<returnvalue>boolean</returnvalue>
</para>
<para>
String matches regular expression, case insensitively
</para>
<para>
<literal>'thomas' ~* 'T.*ma'</literal>
<returnvalue>t</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<type>text</type> <literal>!~</literal> <type>text</type>
<returnvalue>boolean</returnvalue>
</para>
<para>
String does not match regular expression, case sensitively
</para>
<para>
<literal>'thomas' !~ 't.*max'</literal>
<returnvalue>t</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<type>text</type> <literal>!~*</literal> <type>text</type>
<returnvalue>boolean</returnvalue>
</para>
<para>
String does not match regular expression, case insensitively
</para>
<para>
<literal>'thomas' !~* 'T.*ma'</literal>
<returnvalue>f</returnvalue>
</para></entry>
</row>
</tbody>
</tgroup>
</table>
<para>
<acronym>POSIX</acronym> regular expressions provide a more
powerful means for pattern matching than the <function>LIKE</function> and
<function>SIMILAR TO</function> operators.
Many Unix tools such as <command>egrep</command>,
<command>sed</command>, or <command>awk</command> use a pattern
matching language that is similar to the one described here.
</para>
<para>
A regular expression is a character sequence that is an
abbreviated definition of a set of strings (a <firstterm>regular
set</firstterm>). A string is said to match a regular expression
if it is a member of the regular set described by the regular
expression. As with <function>LIKE</function>, pattern characters
match string characters exactly unless they are special characters
in the regular expression language — but regular expressions use
different special characters than <function>LIKE</function> does.
Unlike <function>LIKE</function> patterns, a
regular expression is allowed to match anywhere within a string, unless
the regular expression is explicitly anchored to the beginning or
end of the string.
</para>
<para>
Some examples:
<programlisting>
'abcd' ~ 'bc' <lineannotation>true</lineannotation>
'abcd' ~ 'a.c' <lineannotation>true — dot matches any character</lineannotation>
'abcd' ~ 'a.*d' <lineannotation>true — <literal>*</literal> repeats the preceding pattern item</lineannotation>
'abcd' ~ '(b|x)' <lineannotation>true — <literal>|</literal> means OR, parentheses group</lineannotation>
'abcd' ~ '^a' <lineannotation>true — <literal>^</literal> anchors to start of string</lineannotation>
'abcd' ~ '^(b|c)' <lineannotation>false — would match except for anchoring</lineannotation>
</programlisting>
</para>
<para>
The <acronym>POSIX</acronym> pattern language is described in much
greater detail below.
</para>
<para>
The <function>substring</function> function with two parameters,
<function>substring(<replaceable>string</replaceable> from
<replaceable>pattern</replaceable>)</function>, provides extraction of a
substring
that matches a POSIX regular expression pattern. It returns null if
there is no match, otherwise the first portion of the text that matched the
pattern. But if the pattern contains any parentheses, the portion
of the text that matched the first parenthesized subexpression (the
one whose left parenthesis comes first) is
returned. You can put parentheses around the whole expression
if you want to use parentheses within it without triggering this
exception. If you need parentheses in the pattern before the
subexpression you want to extract, see the non-capturing parentheses
described below.
</para>
<para>
Some examples:
<programlisting>
substring('foobar' from 'o.b') <lineannotation>oob</lineannotation>
substring('foobar' from 'o(.)b') <lineannotation>o</lineannotation>
</programlisting>
</para>
<para>
The <function>regexp_replace</function> function provides substitution of
new text for substrings that match POSIX regular expression patterns.
It has the syntax
<function>regexp_replace</function>(<replaceable>source</replaceable>,
<replaceable>pattern</replaceable>, <replaceable>replacement</replaceable>
<optional>, <replaceable>flags</replaceable> </optional>).
The <replaceable>source</replaceable> string is returned unchanged if
there is no match to the <replaceable>pattern</replaceable>. If there is a
match, the <replaceable>source</replaceable> string is returned with the
<replaceable>replacement</replaceable> string substituted for the matching
substring. The <replaceable>replacement</replaceable> string can contain
<literal>\</literal><replaceable>n</replaceable>, where <replaceable>n</replaceable> is 1
through 9, to indicate that the source substring matching the
<replaceable>n</replaceable>'th parenthesized subexpression of the pattern should be
inserted, and it can contain <literal>\&</literal> to indicate that the
substring matching the entire pattern should be inserted. Write
<literal>\\</literal> if you need to put a literal backslash in the replacement
text.
The <replaceable>flags</replaceable> parameter is an optional text
string containing zero or more single-letter flags that change the
function's behavior. Flag <literal>i</literal> specifies case-insensitive
matching, while flag <literal>g</literal> specifies replacement of each matching
substring rather than only the first one. Supported flags (though
not <literal>g</literal>) are
described in <xref linkend="posix-embedded-options-table"/>.
</para>
<para>
Some examples:
<programlisting>
regexp_replace('foobarbaz', 'b..', 'X')
<lineannotation>fooXbaz</lineannotation>
regexp_replace('foobarbaz', 'b..', 'X', 'g')
<lineannotation>fooXX</lineannotation>
regexp_replace('foobarbaz', 'b(..)', 'X\1Y', 'g')
<lineannotation>fooXarYXazY</lineannotation>
</programlisting>
</para>
<para>
The <function>regexp_match</function> function returns a text array of
captured substring(s) resulting from the first match of a POSIX
regular expression pattern to a string. It has the syntax
<function>regexp_match</function>(<replaceable>string</replaceable>,
<replaceable>pattern</replaceable> <optional>, <replaceable>flags</replaceable> </optional>).
If there is no match, the result is <literal>NULL</literal>.
If a match is found, and the <replaceable>pattern</replaceable> contains no
parenthesized subexpressions, then the result is a single-element text
array containing the substring matching the whole pattern.
If a match is found, and the <replaceable>pattern</replaceable> contains
parenthesized subexpressions, then the result is a text array
whose <replaceable>n</replaceable>'th element is the substring matching
the <replaceable>n</replaceable>'th parenthesized subexpression of
the <replaceable>pattern</replaceable> (not counting <quote>non-capturing</quote>
parentheses; see below for details).
The <replaceable>flags</replaceable> parameter is an optional text string
containing zero or more single-letter flags that change the function's
behavior. Supported flags are described
in <xref linkend="posix-embedded-options-table"/>.
</para>
<para>
Some examples:
<programlisting>
SELECT regexp_match('foobarbequebaz', 'bar.*que');
regexp_match
--------------
{barbeque}
(1 row)
SELECT regexp_match('foobarbequebaz', '(bar)(beque)');
regexp_match
--------------
{bar,beque}
(1 row)
</programlisting>
In the common case where you just want the whole matching substring
or <literal>NULL</literal> for no match, write something like
<programlisting>
SELECT (regexp_match('foobarbequebaz', 'bar.*que'))[1];
regexp_match
--------------
barbeque
(1 row)
</programlisting>
</para>
<para>
The <function>regexp_matches</function> function returns a set of text arrays
of captured substring(s) resulting from matching a POSIX regular
expression pattern to a string. It has the same syntax as
<function>regexp_match</function>.
This function returns no rows if there is no match, one row if there is
a match and the <literal>g</literal> flag is not given, or <replaceable>N</replaceable>
rows if there are <replaceable>N</replaceable> matches and the <literal>g</literal> flag
is given. Each returned row is a text array containing the whole
matched substring or the substrings matching parenthesized
subexpressions of the <replaceable>pattern</replaceable>, just as described above
for <function>regexp_match</function>.
<function>regexp_matches</function> accepts all the flags shown
in <xref linkend="posix-embedded-options-table"/>, plus
the <literal>g</literal> flag which commands it to return all matches, not
just the first one.
</para>
<para>
Some examples:
<programlisting>
SELECT regexp_matches('foo', 'not there');
regexp_matches
----------------
(0 rows)
SELECT regexp_matches('foobarbequebazilbarfbonk', '(b[^b]+)(b[^b]+)', 'g');
regexp_matches
----------------
{bar,beque}
{bazil,barf}
(2 rows)
</programlisting>
</para>
<tip>
<para>
In most cases <function>regexp_matches()</function> should be used with
the <literal>g</literal> flag, since if you only want the first match, it's
easier and more efficient to use <function>regexp_match()</function>.
However, <function>regexp_match()</function> only exists
in <productname>PostgreSQL</productname> version 10 and up. When working in older
versions, a common trick is to place a <function>regexp_matches()</function>
call in a sub-select, for example:
<programlisting>
SELECT col1, (SELECT regexp_matches(col2, '(bar)(beque)')) FROM tab;
</programlisting>
This produces a text array if there's a match, or <literal>NULL</literal> if
not, the same as <function>regexp_match()</function> would do. Without the
sub-select, this query would produce no output at all for table rows
without a match, which is typically not the desired behavior.
</para>
</tip>
<para>
The <function>regexp_split_to_table</function> function splits a string using a POSIX
regular expression pattern as a delimiter. It has the syntax
<function>regexp_split_to_table</function>(<replaceable>string</replaceable>, <replaceable>pattern</replaceable>
<optional>, <replaceable>flags</replaceable> </optional>).
If there is no match to the <replaceable>pattern</replaceable>, the function returns the
<replaceable>string</replaceable>. If there is at least one match, for each match it returns
the text from the end of the last match (or the beginning of the string)
to the beginning of the match. When there are no more matches, it
returns the text from the end of the last match to the end of the string.
The <replaceable>flags</replaceable> parameter is an optional text string containing
zero or more single-letter flags that change the function's behavior.
<function>regexp_split_to_table</function> supports the flags described in
<xref linkend="posix-embedded-options-table"/>.
</para>
<para>
The <function>regexp_split_to_array</function> function behaves the same as
<function>regexp_split_to_table</function>, except that <function>regexp_split_to_array</function>
returns its result as an array of <type>text</type>. It has the syntax
<function>regexp_split_to_array</function>(<replaceable>string</replaceable>, <replaceable>pattern</replaceable>
<optional>, <replaceable>flags</replaceable> </optional>).
The parameters are the same as for <function>regexp_split_to_table</function>.
</para>
<para>
Some examples:
<programlisting>
SELECT foo FROM regexp_split_to_table('the quick brown fox jumps over the lazy dog', '\s+') AS foo;
foo
-------
the
quick
brown
fox
jumps
over
the
lazy
dog
(9 rows)
SELECT regexp_split_to_array('the quick brown fox jumps over the lazy dog', '\s+');
regexp_split_to_array
-----------------------------------------------
{the,quick,brown,fox,jumps,over,the,lazy,dog}
(1 row)
SELECT foo FROM regexp_split_to_table('the quick brown fox', '\s*') AS foo;
foo
-----
t
h
e
q
u
i
c
k
b
r
o
w
n
f
o
x
(16 rows)
</programlisting>
</para>
<para>
As the last example demonstrates, the regexp split functions ignore
zero-length matches that occur at the start or end of the string
or immediately after a previous match. This is contrary to the strict
definition of regexp matching that is implemented by
<function>regexp_match</function> and
<function>regexp_matches</function>, but is usually the most convenient behavior
in practice. Other software systems such as Perl use similar definitions.
</para>
<!-- derived from the re_syntax.n man page -->
<sect3 id="posix-syntax-details">
<title>Regular Expression Details</title>
<para>
<productname>PostgreSQL</productname>'s regular expressions are implemented
using a software package written by Henry Spencer. Much of
the description of regular expressions below is copied verbatim from his
manual.
</para>
<para>
Regular expressions (<acronym>RE</acronym>s), as defined in
<acronym>POSIX</acronym> 1003.2, come in two forms:
<firstterm>extended</firstterm> <acronym>RE</acronym>s or <acronym>ERE</acronym>s
(roughly those of <command>egrep</command>), and
<firstterm>basic</firstterm> <acronym>RE</acronym>s or <acronym>BRE</acronym>s
(roughly those of <command>ed</command>).
<productname>PostgreSQL</productname> supports both forms, and
also implements some extensions
that are not in the POSIX standard, but have become widely used
due to their availability in programming languages such as Perl and Tcl.
<acronym>RE</acronym>s using these non-POSIX extensions are called
<firstterm>advanced</firstterm> <acronym>RE</acronym>s or <acronym>ARE</acronym>s
in this documentation. AREs are almost an exact superset of EREs,
but BREs have several notational incompatibilities (as well as being
much more limited).
We first describe the ARE and ERE forms, noting features that apply
only to AREs, and then describe how BREs differ.
</para>
<note>
<para>
<productname>PostgreSQL</productname> always initially presumes that a regular
expression follows the ARE rules. However, the more limited ERE or
BRE rules can be chosen by prepending an <firstterm>embedded option</firstterm>
to the RE pattern, as described in <xref linkend="posix-metasyntax"/>.
This can be useful for compatibility with applications that expect
exactly the <acronym>POSIX</acronym> 1003.2 rules.
</para>
</note>
<para>
A regular expression is defined as one or more
<firstterm>branches</firstterm>, separated by
<literal>|</literal>. It matches anything that matches one of the
branches.
</para>
<para>
A branch is zero or more <firstterm>quantified atoms</firstterm> or
<firstterm>constraints</firstterm>, concatenated.
It matches a match for the first, followed by a match for the second, etc;
an empty branch matches the empty string.
</para>
<para>
A quantified atom is an <firstterm>atom</firstterm> possibly followed
by a single <firstterm>quantifier</firstterm>.
Without a quantifier, it matches a match for the atom.
With a quantifier, it can match some number of matches of the atom.
An <firstterm>atom</firstterm> can be any of the possibilities
shown in <xref linkend="posix-atoms-table"/>.
The possible quantifiers and their meanings are shown in
<xref linkend="posix-quantifiers-table"/>.
</para>
<para>
A <firstterm>constraint</firstterm> matches an empty string, but matches only when
specific conditions are met. A constraint can be used where an atom
could be used, except it cannot be followed by a quantifier.
The simple constraints are shown in
<xref linkend="posix-constraints-table"/>;
some more constraints are described later.
</para>
<table id="posix-atoms-table">
<title>Regular Expression Atoms</title>
<tgroup cols="2">
<thead>
<row>
<entry>Atom</entry>
<entry>Description</entry>
</row>
</thead>
<tbody>
<row>
<entry> <literal>(</literal><replaceable>re</replaceable><literal>)</literal> </entry>
<entry> (where <replaceable>re</replaceable> is any regular expression)
matches a match for
<replaceable>re</replaceable>, with the match noted for possible reporting </entry>
</row>
<row>
<entry> <literal>(?:</literal><replaceable>re</replaceable><literal>)</literal> </entry>
<entry> as above, but the match is not noted for reporting
(a <quote>non-capturing</quote> set of parentheses)
(AREs only) </entry>
</row>
<row>
<entry> <literal>.</literal> </entry>
<entry> matches any single character </entry>
</row>
<row>
<entry> <literal>[</literal><replaceable>chars</replaceable><literal>]</literal> </entry>
<entry> a <firstterm>bracket expression</firstterm>,
matching any one of the <replaceable>chars</replaceable> (see
<xref linkend="posix-bracket-expressions"/> for more detail) </entry>
</row>
<row>
<entry> <literal>\</literal><replaceable>k</replaceable> </entry>
<entry> (where <replaceable>k</replaceable> is a non-alphanumeric character)
matches that character taken as an ordinary character,
e.g., <literal>\\</literal> matches a backslash character </entry>
</row>
<row>
<entry> <literal>\</literal><replaceable>c</replaceable> </entry>
<entry> where <replaceable>c</replaceable> is alphanumeric
(possibly followed by other characters)
is an <firstterm>escape</firstterm>, see <xref linkend="posix-escape-sequences"/>
(AREs only; in EREs and BREs, this matches <replaceable>c</replaceable>) </entry>
</row>
<row>
<entry> <literal>{</literal> </entry>
<entry> when followed by a character other than a digit,
matches the left-brace character <literal>{</literal>;
when followed by a digit, it is the beginning of a
<replaceable>bound</replaceable> (see below) </entry>
</row>
<row>
<entry> <replaceable>x</replaceable> </entry>
<entry> where <replaceable>x</replaceable> is a single character with no other
significance, matches that character </entry>
</row>
</tbody>
</tgroup>
</table>
<para>
An RE cannot end with a backslash (<literal>\</literal>).
</para>
<note>
<para>
If you have <xref linkend="guc-standard-conforming-strings"/> turned off,
any backslashes you write in literal string constants will need to be
doubled. See <xref linkend="sql-syntax-strings"/> for more information.
</para>
</note>
<table id="posix-quantifiers-table">
<title>Regular Expression Quantifiers</title>
<tgroup cols="2">
<thead>
<row>
<entry>Quantifier</entry>
<entry>Matches</entry>
</row>
</thead>
<tbody>
<row>
<entry> <literal>*</literal> </entry>
<entry> a sequence of 0 or more matches of the atom </entry>
</row>
<row>
<entry> <literal>+</literal> </entry>
<entry> a sequence of 1 or more matches of the atom </entry>
</row>
<row>
<entry> <literal>?</literal> </entry>
<entry> a sequence of 0 or 1 matches of the atom </entry>
</row>
<row>
<entry> <literal>{</literal><replaceable>m</replaceable><literal>}</literal> </entry>
<entry> a sequence of exactly <replaceable>m</replaceable> matches of the atom </entry>
</row>
<row>
<entry> <literal>{</literal><replaceable>m</replaceable><literal>,}</literal> </entry>
<entry> a sequence of <replaceable>m</replaceable> or more matches of the atom </entry>
</row>
<row>
<entry>
<literal>{</literal><replaceable>m</replaceable><literal>,</literal><replaceable>n</replaceable><literal>}</literal> </entry>
<entry> a sequence of <replaceable>m</replaceable> through <replaceable>n</replaceable>
(inclusive) matches of the atom; <replaceable>m</replaceable> cannot exceed
<replaceable>n</replaceable> </entry>
</row>
<row>
<entry> <literal>*?</literal> </entry>
<entry> non-greedy version of <literal>*</literal> </entry>
</row>
<row>
<entry> <literal>+?</literal> </entry>
<entry> non-greedy version of <literal>+</literal> </entry>
</row>
<row>
<entry> <literal>??</literal> </entry>
<entry> non-greedy version of <literal>?</literal> </entry>
</row>
<row>
<entry> <literal>{</literal><replaceable>m</replaceable><literal>}?</literal> </entry>
<entry> non-greedy version of <literal>{</literal><replaceable>m</replaceable><literal>}</literal> </entry>
</row>
<row>
<entry> <literal>{</literal><replaceable>m</replaceable><literal>,}?</literal> </entry>
<entry> non-greedy version of <literal>{</literal><replaceable>m</replaceable><literal>,}</literal> </entry>
</row>
<row>
<entry>
<literal>{</literal><replaceable>m</replaceable><literal>,</literal><replaceable>n</replaceable><literal>}?</literal> </entry>
<entry> non-greedy version of <literal>{</literal><replaceable>m</replaceable><literal>,</literal><replaceable>n</replaceable><literal>}</literal> </entry>
</row>
</tbody>
</tgroup>
</table>
<para>
The forms using <literal>{</literal><replaceable>...</replaceable><literal>}</literal>
are known as <firstterm>bounds</firstterm>.
The numbers <replaceable>m</replaceable> and <replaceable>n</replaceable> within a bound are
unsigned decimal integers with permissible values from 0 to 255 inclusive.
</para>
<para>
<firstterm>Non-greedy</firstterm> quantifiers (available in AREs only) match the
same possibilities as their corresponding normal (<firstterm>greedy</firstterm>)
counterparts, but prefer the smallest number rather than the largest
number of matches.
See <xref linkend="posix-matching-rules"/> for more detail.
</para>
<note>
<para>
A quantifier cannot immediately follow another quantifier, e.g.,
<literal>**</literal> is invalid.
A quantifier cannot
begin an expression or subexpression or follow
<literal>^</literal> or <literal>|</literal>.
</para>
</note>
<table id="posix-constraints-table">
<title>Regular Expression Constraints</title>
<tgroup cols="2">
<thead>
<row>
<entry>Constraint</entry>
<entry>Description</entry>
</row>
</thead>
<tbody>
<row>
<entry> <literal>^</literal> </entry>
<entry> matches at the beginning of the string </entry>
</row>
<row>
<entry> <literal>$</literal> </entry>
<entry> matches at the end of the string </entry>
</row>
<row>
<entry> <literal>(?=</literal><replaceable>re</replaceable><literal>)</literal> </entry>
<entry> <firstterm>positive lookahead</firstterm> matches at any point
where a substring matching <replaceable>re</replaceable> begins
(AREs only) </entry>
</row>
<row>
<entry> <literal>(?!</literal><replaceable>re</replaceable><literal>)</literal> </entry>
<entry> <firstterm>negative lookahead</firstterm> matches at any point
where no substring matching <replaceable>re</replaceable> begins
(AREs only) </entry>
</row>
<row>
<entry> <literal>(?<=</literal><replaceable>re</replaceable><literal>)</literal> </entry>
<entry> <firstterm>positive lookbehind</firstterm> matches at any point
where a substring matching <replaceable>re</replaceable> ends
(AREs only) </entry>
</row>
<row>
<entry> <literal>(?<!</literal><replaceable>re</replaceable><literal>)</literal> </entry>
<entry> <firstterm>negative lookbehind</firstterm> matches at any point
where no substring matching <replaceable>re</replaceable> ends
(AREs only) </entry>
</row>
</tbody>
</tgroup>
</table>
<para>
Lookahead and lookbehind constraints cannot contain <firstterm>back
references</firstterm> (see <xref linkend="posix-escape-sequences"/>),
and all parentheses within them are considered non-capturing.
</para>
</sect3>
<sect3 id="posix-bracket-expressions">
<title>Bracket Expressions</title>
<para>
A <firstterm>bracket expression</firstterm> is a list of
characters enclosed in <literal>[]</literal>. It normally matches
any single character from the list (but see below). If the list
begins with <literal>^</literal>, it matches any single character
<emphasis>not</emphasis> from the rest of the list.
If two characters
in the list are separated by <literal>-</literal>, this is
shorthand for the full range of characters between those two
(inclusive) in the collating sequence,
e.g., <literal>[0-9]</literal> in <acronym>ASCII</acronym> matches
any decimal digit. It is illegal for two ranges to share an
endpoint, e.g., <literal>a-c-e</literal>. Ranges are very
collating-sequence-dependent, so portable programs should avoid
relying on them.
</para>
<para>
To include a literal <literal>]</literal> in the list, make it the
first character (after <literal>^</literal>, if that is used). To
include a literal <literal>-</literal>, make it the first or last
character, or the second endpoint of a range. To use a literal
<literal>-</literal> as the first endpoint of a range, enclose it
in <literal>[.</literal> and <literal>.]</literal> to make it a
collating element (see below). With the exception of these characters,
some combinations using <literal>[</literal>
(see next paragraphs), and escapes (AREs only), all other special
characters lose their special significance within a bracket expression.
In particular, <literal>\</literal> is not special when following
ERE or BRE rules, though it is special (as introducing an escape)
in AREs.
</para>
<para>
Within a bracket expression, a collating element (a character, a
multiple-character sequence that collates as if it were a single
character, or a collating-sequence name for either) enclosed in
<literal>[.</literal> and <literal>.]</literal> stands for the
sequence of characters of that collating element. The sequence is
treated as a single element of the bracket expression's list. This
allows a bracket
expression containing a multiple-character collating element to
match more than one character, e.g., if the collating sequence
includes a <literal>ch</literal> collating element, then the RE
<literal>[[.ch.]]*c</literal> matches the first five characters of
<literal>chchcc</literal>.
</para>
<note>
<para>
<productname>PostgreSQL</productname> currently does not support multi-character collating
elements. This information describes possible future behavior.
</para>
</note>
<para>
Within a bracket expression, a collating element enclosed in
<literal>[=</literal> and <literal>=]</literal> is an <firstterm>equivalence
class</firstterm>, standing for the sequences of characters of all collating
elements equivalent to that one, including itself. (If there are
no other equivalent collating elements, the treatment is as if the
enclosing delimiters were <literal>[.</literal> and
<literal>.]</literal>.) For example, if <literal>o</literal> and
<literal>^</literal> are the members of an equivalence class, then
<literal>[[=o=]]</literal>, <literal>[[=^=]]</literal>, and
<literal>[o^]</literal> are all synonymous. An equivalence class
cannot be an endpoint of a range.
</para>
<para>
Within a bracket expression, the name of a character class
enclosed in <literal>[:</literal> and <literal>:]</literal> stands
for the list of all characters belonging to that class. A character
class cannot be used as an endpoint of a range.
The <acronym>POSIX</acronym> standard defines these character class
names:
<literal>alnum</literal> (letters and numeric digits),
<literal>alpha</literal> (letters),
<literal>blank</literal> (space and tab),
<literal>cntrl</literal> (control characters),
<literal>digit</literal> (numeric digits),
<literal>graph</literal> (printable characters except space),
<literal>lower</literal> (lower-case letters),
<literal>print</literal> (printable characters including space),
<literal>punct</literal> (punctuation),
<literal>space</literal> (any white space),
<literal>upper</literal> (upper-case letters),
and <literal>xdigit</literal> (hexadecimal digits).
The behavior of these standard character classes is generally
consistent across platforms for characters in the 7-bit ASCII set.
Whether a given non-ASCII character is considered to belong to one
of these classes depends on the <firstterm>collation</firstterm>
that is used for the regular-expression function or operator
(see <xref linkend="collation"/>), or by default on the
database's <envar>LC_CTYPE</envar> locale setting (see
<xref linkend="locale"/>). The classification of non-ASCII
characters can vary across platforms even in similarly-named
locales. (But the <literal>C</literal> locale never considers any
non-ASCII characters to belong to any of these classes.)
In addition to these standard character
classes, <productname>PostgreSQL</productname> defines
the <literal>word</literal> character class, which is the same as
<literal>alnum</literal> plus the underscore (<literal>_</literal>)
character, and
the <literal>ascii</literal> character class, which contains exactly
the 7-bit ASCII set.
</para>
<para>
There are two special cases of bracket expressions: the bracket
expressions <literal>[[:<:]]</literal> and
<literal>[[:>:]]</literal> are constraints,
matching empty strings at the beginning
and end of a word respectively. A word is defined as a sequence
of word characters that is neither preceded nor followed by word
characters. A word character is any character belonging to the
<literal>word</literal> character class, that is, any letter, digit,
or underscore. This is an extension, compatible with but not
specified by <acronym>POSIX</acronym> 1003.2, and should be used with
caution in software intended to be portable to other systems.
The constraint escapes described below are usually preferable; they
are no more standard, but are easier to type.
</para>
</sect3>
<sect3 id="posix-escape-sequences">
<title>Regular Expression Escapes</title>
<para>
<firstterm>Escapes</firstterm> are special sequences beginning with <literal>\</literal>
followed by an alphanumeric character. Escapes come in several varieties:
character entry, class shorthands, constraint escapes, and back references.
A <literal>\</literal> followed by an alphanumeric character but not constituting
a valid escape is illegal in AREs.
In EREs, there are no escapes: outside a bracket expression,
a <literal>\</literal> followed by an alphanumeric character merely stands for
that character as an ordinary character, and inside a bracket expression,
<literal>\</literal> is an ordinary character.
(The latter is the one actual incompatibility between EREs and AREs.)
</para>
<para>
<firstterm>Character-entry escapes</firstterm> exist to make it easier to specify
non-printing and other inconvenient characters in REs. They are
shown in <xref linkend="posix-character-entry-escapes-table"/>.
</para>
<para>
<firstterm>Class-shorthand escapes</firstterm> provide shorthands for certain
commonly-used character classes. They are
shown in <xref linkend="posix-class-shorthand-escapes-table"/>.
</para>
<para>
A <firstterm>constraint escape</firstterm> is a constraint,
matching the empty string if specific conditions are met,
written as an escape. They are
shown in <xref linkend="posix-constraint-escapes-table"/>.
</para>
<para>
A <firstterm>back reference</firstterm> (<literal>\</literal><replaceable>n</replaceable>) matches the
same string matched by the previous parenthesized subexpression specified
by the number <replaceable>n</replaceable>
(see <xref linkend="posix-constraint-backref-table"/>). For example,
<literal>([bc])\1</literal> matches <literal>bb</literal> or <literal>cc</literal>
but not <literal>bc</literal> or <literal>cb</literal>.
The subexpression must entirely precede the back reference in the RE.
Subexpressions are numbered in the order of their leading parentheses.
Non-capturing parentheses do not define subexpressions.
The back reference considers only the string characters matched by the
referenced subexpression, not any constraints contained in it. For
example, <literal>(^\d)\1</literal> will match <literal>22</literal>.
</para>
<table id="posix-character-entry-escapes-table">
<title>Regular Expression Character-Entry Escapes</title>
<tgroup cols="2">
<thead>
<row>
<entry>Escape</entry>
<entry>Description</entry>
</row>
</thead>
<tbody>
<row>
<entry> <literal>\a</literal> </entry>
<entry> alert (bell) character, as in C </entry>
</row>
<row>
<entry> <literal>\b</literal> </entry>
<entry> backspace, as in C </entry>
</row>
<row>
<entry> <literal>\B</literal> </entry>
<entry> synonym for backslash (<literal>\</literal>) to help reduce the need for backslash
doubling </entry>
</row>
<row>
<entry> <literal>\c</literal><replaceable>X</replaceable> </entry>
<entry> (where <replaceable>X</replaceable> is any character) the character whose
low-order 5 bits are the same as those of
<replaceable>X</replaceable>, and whose other bits are all zero </entry>
</row>
<row>
<entry> <literal>\e</literal> </entry>
<entry> the character whose collating-sequence name
is <literal>ESC</literal>,
or failing that, the character with octal value <literal>033</literal> </entry>
</row>
<row>
<entry> <literal>\f</literal> </entry>
<entry> form feed, as in C </entry>
</row>
<row>
<entry> <literal>\n</literal> </entry>
<entry> newline, as in C </entry>
</row>
<row>
<entry> <literal>\r</literal> </entry>
<entry> carriage return, as in C </entry>
</row>
<row>
<entry> <literal>\t</literal> </entry>
<entry> horizontal tab, as in C </entry>
</row>
<row>
<entry> <literal>\u</literal><replaceable>wxyz</replaceable> </entry>
<entry> (where <replaceable>wxyz</replaceable> is exactly four hexadecimal digits)
the character whose hexadecimal value is
<literal>0x</literal><replaceable>wxyz</replaceable>
</entry>
</row>
<row>
<entry> <literal>\U</literal><replaceable>stuvwxyz</replaceable> </entry>
<entry> (where <replaceable>stuvwxyz</replaceable> is exactly eight hexadecimal
digits)
the character whose hexadecimal value is
<literal>0x</literal><replaceable>stuvwxyz</replaceable>
</entry>
</row>
<row>
<entry> <literal>\v</literal> </entry>
<entry> vertical tab, as in C </entry>
</row>
<row>
<entry> <literal>\x</literal><replaceable>hhh</replaceable> </entry>
<entry> (where <replaceable>hhh</replaceable> is any sequence of hexadecimal
digits)
the character whose hexadecimal value is
<literal>0x</literal><replaceable>hhh</replaceable>
(a single character no matter how many hexadecimal digits are used)
</entry>
</row>
<row>
<entry> <literal>\0</literal> </entry>
<entry> the character whose value is <literal>0</literal> (the null byte)</entry>
</row>
<row>
<entry> <literal>\</literal><replaceable>xy</replaceable> </entry>
<entry> (where <replaceable>xy</replaceable> is exactly two octal digits,
and is not a <firstterm>back reference</firstterm>)
the character whose octal value is
<literal>0</literal><replaceable>xy</replaceable> </entry>
</row>
<row>
<entry> <literal>\</literal><replaceable>xyz</replaceable> </entry>
<entry> (where <replaceable>xyz</replaceable> is exactly three octal digits,
and is not a <firstterm>back reference</firstterm>)
the character whose octal value is
<literal>0</literal><replaceable>xyz</replaceable> </entry>
</row>
</tbody>
</tgroup>
</table>
<para>
Hexadecimal digits are <literal>0</literal>-<literal>9</literal>,
<literal>a</literal>-<literal>f</literal>, and <literal>A</literal>-<literal>F</literal>.
Octal digits are <literal>0</literal>-<literal>7</literal>.
</para>
<para>
Numeric character-entry escapes specifying values outside the ASCII range
(0–127) have meanings dependent on the database encoding. When the
encoding is UTF-8, escape values are equivalent to Unicode code points,
for example <literal>\u1234</literal> means the character <literal>U+1234</literal>.
For other multibyte encodings, character-entry escapes usually just
specify the concatenation of the byte values for the character. If the
escape value does not correspond to any legal character in the database
encoding, no error will be raised, but it will never match any data.
</para>
<para>
The character-entry escapes are always taken as ordinary characters.
For example, <literal>\135</literal> is <literal>]</literal> in ASCII, but
<literal>\135</literal> does not terminate a bracket expression.
</para>
<table id="posix-class-shorthand-escapes-table">
<title>Regular Expression Class-Shorthand Escapes</title>
<tgroup cols="2">
<thead>
<row>
<entry>Escape</entry>
<entry>Description</entry>
</row>
</thead>
<tbody>
<row>
<entry> <literal>\d</literal> </entry>
<entry> matches any digit, like
<literal>[[:digit:]]</literal> </entry>
</row>
<row>
<entry> <literal>\s</literal> </entry>
<entry> matches any whitespace character, like
<literal>[[:space:]]</literal> </entry>
</row>
<row>
<entry> <literal>\w</literal> </entry>
<entry> matches any word character, like
<literal>[[:word:]]</literal> </entry>
</row>
<row>
<entry> <literal>\D</literal> </entry>
<entry> matches any non-digit, like
<literal>[^[:digit:]]</literal> </entry>
</row>
<row>
<entry> <literal>\S</literal> </entry>
<entry> matches any non-whitespace character, like
<literal>[^[:space:]]</literal> </entry>
</row>
<row>
<entry> <literal>\W</literal> </entry>
<entry> matches any non-word character, like
<literal>[^[:word:]]</literal> </entry>
</row>
</tbody>
</tgroup>
</table>
<para>
The class-shorthand escapes also work within bracket expressions,
although the definitions shown above are not quite syntactically
valid in that context.
For example, <literal>[a-c\d]</literal> is equivalent to
<literal>[a-c[:digit:]]</literal>.
</para>
<table id="posix-constraint-escapes-table">
<title>Regular Expression Constraint Escapes</title>
<tgroup cols="2">
<thead>
<row>
<entry>Escape</entry>
<entry>Description</entry>
</row>
</thead>
<tbody>
<row>
<entry> <literal>\A</literal> </entry>
<entry> matches only at the beginning of the string
(see <xref linkend="posix-matching-rules"/> for how this differs from
<literal>^</literal>) </entry>
</row>
<row>
<entry> <literal>\m</literal> </entry>
<entry> matches only at the beginning of a word </entry>
</row>
<row>
<entry> <literal>\M</literal> </entry>
<entry> matches only at the end of a word </entry>
</row>
<row>
<entry> <literal>\y</literal> </entry>
<entry> matches only at the beginning or end of a word </entry>
</row>
<row>
<entry> <literal>\Y</literal> </entry>
<entry> matches only at a point that is not the beginning or end of a
word </entry>
</row>
<row>
<entry> <literal>\Z</literal> </entry>
<entry> matches only at the end of the string
(see <xref linkend="posix-matching-rules"/> for how this differs from
<literal>$</literal>) </entry>
</row>
</tbody>
</tgroup>
</table>
<para>
A word is defined as in the specification of
<literal>[[:<:]]</literal> and <literal>[[:>:]]</literal> above.
Constraint escapes are illegal within bracket expressions.
</para>
<table id="posix-constraint-backref-table">
<title>Regular Expression Back References</title>
<tgroup cols="2">
<thead>
<row>
<entry>Escape</entry>
<entry>Description</entry>
</row>
</thead>
<tbody>
<row>
<entry> <literal>\</literal><replaceable>m</replaceable> </entry>
<entry> (where <replaceable>m</replaceable> is a nonzero digit)
a back reference to the <replaceable>m</replaceable>'th subexpression </entry>
</row>
<row>
<entry> <literal>\</literal><replaceable>mnn</replaceable> </entry>
<entry> (where <replaceable>m</replaceable> is a nonzero digit, and
<replaceable>nn</replaceable> is some more digits, and the decimal value
<replaceable>mnn</replaceable> is not greater than the number of closing capturing
parentheses seen so far)
a back reference to the <replaceable>mnn</replaceable>'th subexpression </entry>
</row>
</tbody>
</tgroup>
</table>
<note>
<para>
There is an inherent ambiguity between octal character-entry
escapes and back references, which is resolved by the following heuristics,
as hinted at above.
A leading zero always indicates an octal escape.
A single non-zero digit, not followed by another digit,
is always taken as a back reference.
A multi-digit sequence not starting with a zero is taken as a back
reference if it comes after a suitable subexpression
(i.e., the number is in the legal range for a back reference),
and otherwise is taken as octal.
</para>
</note>
</sect3>
<sect3 id="posix-metasyntax">
<title>Regular Expression Metasyntax</title>
<para>
In addition to the main syntax described above, there are some special
forms and miscellaneous syntactic facilities available.
</para>
<para>
An RE can begin with one of two special <firstterm>director</firstterm> prefixes.
If an RE begins with <literal>***:</literal>,
the rest of the RE is taken as an ARE. (This normally has no effect in
<productname>PostgreSQL</productname>, since REs are assumed to be AREs;
but it does have an effect if ERE or BRE mode had been specified by
the <replaceable>flags</replaceable> parameter to a regex function.)
If an RE begins with <literal>***=</literal>,
the rest of the RE is taken to be a literal string,
with all characters considered ordinary characters.
</para>
<para>
An ARE can begin with <firstterm>embedded options</firstterm>:
a sequence <literal>(?</literal><replaceable>xyz</replaceable><literal>)</literal>
(where <replaceable>xyz</replaceable> is one or more alphabetic characters)
specifies options affecting the rest of the RE.
These options override any previously determined options —
in particular, they can override the case-sensitivity behavior implied by
a regex operator, or the <replaceable>flags</replaceable> parameter to a regex
function.
The available option letters are
shown in <xref linkend="posix-embedded-options-table"/>.
Note that these same option letters are used in the <replaceable>flags</replaceable>
parameters of regex functions.
</para>
<table id="posix-embedded-options-table">
<title>ARE Embedded-Option Letters</title>
<tgroup cols="2">
<thead>
<row>
<entry>Option</entry>
<entry>Description</entry>
</row>
</thead>
<tbody>
<row>
<entry> <literal>b</literal> </entry>
<entry> rest of RE is a BRE </entry>
</row>
<row>
<entry> <literal>c</literal> </entry>
<entry> case-sensitive matching (overrides operator type) </entry>
</row>
<row>
<entry> <literal>e</literal> </entry>
<entry> rest of RE is an ERE </entry>
</row>
<row>
<entry> <literal>i</literal> </entry>
<entry> case-insensitive matching (see
<xref linkend="posix-matching-rules"/>) (overrides operator type) </entry>
</row>
<row>
<entry> <literal>m</literal> </entry>
<entry> historical synonym for <literal>n</literal> </entry>
</row>
<row>
<entry> <literal>n</literal> </entry>
<entry> newline-sensitive matching (see
<xref linkend="posix-matching-rules"/>) </entry>
</row>
<row>
<entry> <literal>p</literal> </entry>
<entry> partial newline-sensitive matching (see
<xref linkend="posix-matching-rules"/>) </entry>
</row>
<row>
<entry> <literal>q</literal> </entry>
<entry> rest of RE is a literal (<quote>quoted</quote>) string, all ordinary
characters </entry>
</row>
<row>
<entry> <literal>s</literal> </entry>
<entry> non-newline-sensitive matching (default) </entry>
</row>
<row>
<entry> <literal>t</literal> </entry>
<entry> tight syntax (default; see below) </entry>
</row>
<row>
<entry> <literal>w</literal> </entry>
<entry> inverse partial newline-sensitive (<quote>weird</quote>) matching
(see <xref linkend="posix-matching-rules"/>) </entry>
</row>
<row>
<entry> <literal>x</literal> </entry>
<entry> expanded syntax (see below) </entry>
</row>
</tbody>
</tgroup>
</table>
<para>
Embedded options take effect at the <literal>)</literal> terminating the sequence.
They can appear only at the start of an ARE (after the
<literal>***:</literal> director if any).
</para>
<para>
In addition to the usual (<firstterm>tight</firstterm>) RE syntax, in which all
characters are significant, there is an <firstterm>expanded</firstterm> syntax,
available by specifying the embedded <literal>x</literal> option.
In the expanded syntax,
white-space characters in the RE are ignored, as are
all characters between a <literal>#</literal>
and the following newline (or the end of the RE). This
permits paragraphing and commenting a complex RE.
There are three exceptions to that basic rule:
<itemizedlist>
<listitem>
<para>
a white-space character or <literal>#</literal> preceded by <literal>\</literal> is
retained
</para>
</listitem>
<listitem>
<para>
white space or <literal>#</literal> within a bracket expression is retained
</para>
</listitem>
<listitem>
<para>
white space and comments cannot appear within multi-character symbols,
such as <literal>(?:</literal>
</para>
</listitem>
</itemizedlist>
For this purpose, white-space characters are blank, tab, newline, and
any character that belongs to the <replaceable>space</replaceable> character class.
</para>
<para>
Finally, in an ARE, outside bracket expressions, the sequence
<literal>(?#</literal><replaceable>ttt</replaceable><literal>)</literal>
(where <replaceable>ttt</replaceable> is any text not containing a <literal>)</literal>)
is a comment, completely ignored.
Again, this is not allowed between the characters of
multi-character symbols, like <literal>(?:</literal>.
Such comments are more a historical artifact than a useful facility,
and their use is deprecated; use the expanded syntax instead.
</para>
<para>
<emphasis>None</emphasis> of these metasyntax extensions is available if
an initial <literal>***=</literal> director
has specified that the user's input be treated as a literal string
rather than as an RE.
</para>
</sect3>
<sect3 id="posix-matching-rules">
<title>Regular Expression Matching Rules</title>
<para>
In the event that an RE could match more than one substring of a given
string, the RE matches the one starting earliest in the string.
If the RE could match more than one substring starting at that point,
either the longest possible match or the shortest possible match will
be taken, depending on whether the RE is <firstterm>greedy</firstterm> or
<firstterm>non-greedy</firstterm>.
</para>
<para>
Whether an RE is greedy or not is determined by the following rules:
<itemizedlist>
<listitem>
<para>
Most atoms, and all constraints, have no greediness attribute (because
they cannot match variable amounts of text anyway).
</para>
</listitem>
<listitem>
<para>
Adding parentheses around an RE does not change its greediness.
</para>
</listitem>
<listitem>
<para>
A quantified atom with a fixed-repetition quantifier
(<literal>{</literal><replaceable>m</replaceable><literal>}</literal>
or
<literal>{</literal><replaceable>m</replaceable><literal>}?</literal>)
has the same greediness (possibly none) as the atom itself.
</para>
</listitem>
<listitem>
<para>
A quantified atom with other normal quantifiers (including
<literal>{</literal><replaceable>m</replaceable><literal>,</literal><replaceable>n</replaceable><literal>}</literal>
with <replaceable>m</replaceable> equal to <replaceable>n</replaceable>)
is greedy (prefers longest match).
</para>
</listitem>
<listitem>
<para>
A quantified atom with a non-greedy quantifier (including
<literal>{</literal><replaceable>m</replaceable><literal>,</literal><replaceable>n</replaceable><literal>}?</literal>
with <replaceable>m</replaceable> equal to <replaceable>n</replaceable>)
is non-greedy (prefers shortest match).
</para>
</listitem>
<listitem>
<para>
A branch — that is, an RE that has no top-level
<literal>|</literal> operator — has the same greediness as the first
quantified atom in it that has a greediness attribute.
</para>
</listitem>
<listitem>
<para>
An RE consisting of two or more branches connected by the
<literal>|</literal> operator is always greedy.
</para>
</listitem>
</itemizedlist>
</para>
<para>
The above rules associate greediness attributes not only with individual
quantified atoms, but with branches and entire REs that contain quantified
atoms. What that means is that the matching is done in such a way that
the branch, or whole RE, matches the longest or shortest possible
substring <emphasis>as a whole</emphasis>. Once the length of the entire match
is determined, the part of it that matches any particular subexpression
is determined on the basis of the greediness attribute of that
subexpression, with subexpressions starting earlier in the RE taking
priority over ones starting later.
</para>
<para>
An example of what this means:
<screen>
SELECT SUBSTRING('XY1234Z', 'Y*([0-9]{1,3})');
<lineannotation>Result: </lineannotation><computeroutput>123</computeroutput>
SELECT SUBSTRING('XY1234Z', 'Y*?([0-9]{1,3})');
<lineannotation>Result: </lineannotation><computeroutput>1</computeroutput>
</screen>
In the first case, the RE as a whole is greedy because <literal>Y*</literal>
is greedy. It can match beginning at the <literal>Y</literal>, and it matches
the longest possible string starting there, i.e., <literal>Y123</literal>.
The output is the parenthesized part of that, or <literal>123</literal>.
In the second case, the RE as a whole is non-greedy because <literal>Y*?</literal>
is non-greedy. It can match beginning at the <literal>Y</literal>, and it matches
the shortest possible string starting there, i.e., <literal>Y1</literal>.
The subexpression <literal>[0-9]{1,3}</literal> is greedy but it cannot change
the decision as to the overall match length; so it is forced to match
just <literal>1</literal>.
</para>
<para>
In short, when an RE contains both greedy and non-greedy subexpressions,
the total match length is either as long as possible or as short as
possible, according to the attribute assigned to the whole RE. The
attributes assigned to the subexpressions only affect how much of that
match they are allowed to <quote>eat</quote> relative to each other.
</para>
<para>
The quantifiers <literal>{1,1}</literal> and <literal>{1,1}?</literal>
can be used to force greediness or non-greediness, respectively,
on a subexpression or a whole RE.
This is useful when you need the whole RE to have a greediness attribute
different from what's deduced from its elements. As an example,
suppose that we are trying to separate a string containing some digits
into the digits and the parts before and after them. We might try to
do that like this:
<screen>
SELECT regexp_match('abc01234xyz', '(.*)(\d+)(.*)');
<lineannotation>Result: </lineannotation><computeroutput>{abc0123,4,xyz}</computeroutput>
</screen>
That didn't work: the first <literal>.*</literal> is greedy so
it <quote>eats</quote> as much as it can, leaving the <literal>\d+</literal> to
match at the last possible place, the last digit. We might try to fix
that by making it non-greedy:
<screen>
SELECT regexp_match('abc01234xyz', '(.*?)(\d+)(.*)');
<lineannotation>Result: </lineannotation><computeroutput>{abc,0,""}</computeroutput>
</screen>
That didn't work either, because now the RE as a whole is non-greedy
and so it ends the overall match as soon as possible. We can get what
we want by forcing the RE as a whole to be greedy:
<screen>
SELECT regexp_match('abc01234xyz', '(?:(.*?)(\d+)(.*)){1,1}');
<lineannotation>Result: </lineannotation><computeroutput>{abc,01234,xyz}</computeroutput>
</screen>
Controlling the RE's overall greediness separately from its components'
greediness allows great flexibility in handling variable-length patterns.
</para>
<para>
When deciding what is a longer or shorter match,
match lengths are measured in characters, not collating elements.
An empty string is considered longer than no match at all.
For example:
<literal>bb*</literal>
matches the three middle characters of <literal>abbbc</literal>;
<literal>(week|wee)(night|knights)</literal>
matches all ten characters of <literal>weeknights</literal>;
when <literal>(.*).*</literal>
is matched against <literal>abc</literal> the parenthesized subexpression
matches all three characters; and when
<literal>(a*)*</literal> is matched against <literal>bc</literal>
both the whole RE and the parenthesized
subexpression match an empty string.
</para>
<para>
If case-independent matching is specified,
the effect is much as if all case distinctions had vanished from the
alphabet.
When an alphabetic that exists in multiple cases appears as an
ordinary character outside a bracket expression, it is effectively
transformed into a bracket expression containing both cases,
e.g., <literal>x</literal> becomes <literal>[xX]</literal>.
When it appears inside a bracket expression, all case counterparts
of it are added to the bracket expression, e.g.,
<literal>[x]</literal> becomes <literal>[xX]</literal>
and <literal>[^x]</literal> becomes <literal>[^xX]</literal>.
</para>
<para>
If newline-sensitive matching is specified, <literal>.</literal>
and bracket expressions using <literal>^</literal>
will never match the newline character
(so that matches will not cross lines unless the RE
explicitly includes a newline)
and <literal>^</literal> and <literal>$</literal>
will match the empty string after and before a newline
respectively, in addition to matching at beginning and end of string
respectively.
But the ARE escapes <literal>\A</literal> and <literal>\Z</literal>
continue to match beginning or end of string <emphasis>only</emphasis>.
Also, the character class shorthands <literal>\D</literal>
and <literal>\W</literal> will match a newline regardless of this mode.
(Before <productname>PostgreSQL</productname> 14, they did not match
newlines when in newline-sensitive mode.
Write <literal>[^[:digit:]]</literal>
or <literal>[^[:word:]]</literal> to get the old behavior.)
</para>
<para>
If partial newline-sensitive matching is specified,
this affects <literal>.</literal> and bracket expressions
as with newline-sensitive matching, but not <literal>^</literal>
and <literal>$</literal>.
</para>
<para>
If inverse partial newline-sensitive matching is specified,
this affects <literal>^</literal> and <literal>$</literal>
as with newline-sensitive matching, but not <literal>.</literal>
and bracket expressions.
This isn't very useful but is provided for symmetry.
</para>
</sect3>
<sect3 id="posix-limits-compatibility">
<title>Limits and Compatibility</title>
<para>
No particular limit is imposed on the length of REs in this
implementation. However,
programs intended to be highly portable should not employ REs longer
than 256 bytes,
as a POSIX-compliant implementation can refuse to accept such REs.
</para>
<para>
The only feature of AREs that is actually incompatible with
POSIX EREs is that <literal>\</literal> does not lose its special
significance inside bracket expressions.
All other ARE features use syntax which is illegal or has
undefined or unspecified effects in POSIX EREs;
the <literal>***</literal> syntax of directors likewise is outside the POSIX
syntax for both BREs and EREs.
</para>
<para>
Many of the ARE extensions are borrowed from Perl, but some have
been changed to clean them up, and a few Perl extensions are not present.
Incompatibilities of note include <literal>\b</literal>, <literal>\B</literal>,
the lack of special treatment for a trailing newline,
the addition of complemented bracket expressions to the things
affected by newline-sensitive matching,
the restrictions on parentheses and back references in lookahead/lookbehind
constraints, and the longest/shortest-match (rather than first-match)
matching semantics.
</para>
</sect3>
<sect3 id="posix-basic-regexes">
<title>Basic Regular Expressions</title>
<para>
BREs differ from EREs in several respects.
In BREs, <literal>|</literal>, <literal>+</literal>, and <literal>?</literal>
are ordinary characters and there is no equivalent
for their functionality.
The delimiters for bounds are
<literal>\{</literal> and <literal>\}</literal>,
with <literal>{</literal> and <literal>}</literal>
by themselves ordinary characters.
The parentheses for nested subexpressions are
<literal>\(</literal> and <literal>\)</literal>,
with <literal>(</literal> and <literal>)</literal> by themselves ordinary characters.
<literal>^</literal> is an ordinary character except at the beginning of the
RE or the beginning of a parenthesized subexpression,
<literal>$</literal> is an ordinary character except at the end of the
RE or the end of a parenthesized subexpression,
and <literal>*</literal> is an ordinary character if it appears at the beginning
of the RE or the beginning of a parenthesized subexpression
(after a possible leading <literal>^</literal>).
Finally, single-digit back references are available, and
<literal>\<</literal> and <literal>\></literal>
are synonyms for
<literal>[[:<:]]</literal> and <literal>[[:>:]]</literal>
respectively; no other escapes are available in BREs.
</para>
</sect3>
<!-- end re_syntax.n man page -->
<sect3 id="posix-vs-xquery">
<title>Differences from XQuery (<literal>LIKE_REGEX</literal>)</title>
<indexterm zone="posix-vs-xquery">
<primary><literal>LIKE_REGEX</literal></primary>
</indexterm>
<indexterm zone="posix-vs-xquery">
<primary>XQuery regular expressions</primary>
</indexterm>
<para>
Since SQL:2008, the SQL standard includes
a <literal>LIKE_REGEX</literal> operator that performs pattern
matching according to the XQuery regular expression
standard. <productname>PostgreSQL</productname> does not yet
implement this operator, but you can get very similar behavior using
the <function>regexp_match()</function> function, since XQuery
regular expressions are quite close to the ARE syntax described above.
</para>
<para>
Notable differences between the existing POSIX-based
regular-expression feature and XQuery regular expressions include:
<itemizedlist>
<listitem>
<para>
XQuery character class subtraction is not supported. An example of
this feature is using the following to match only English
consonants: <literal>[a-z-[aeiou]]</literal>.
</para>
</listitem>
<listitem>
<para>
XQuery character class shorthands <literal>\c</literal>,
<literal>\C</literal>, <literal>\i</literal>,
and <literal>\I</literal> are not supported.
</para>
</listitem>
<listitem>
<para>
XQuery character class elements
using <literal>\p{UnicodeProperty}</literal> or the
inverse <literal>\P{UnicodeProperty}</literal> are not supported.
</para>
</listitem>
<listitem>
<para>
POSIX interprets character classes such as <literal>\w</literal>
(see <xref linkend="posix-class-shorthand-escapes-table"/>)
according to the prevailing locale (which you can control by
attaching a <literal>COLLATE</literal> clause to the operator or
function). XQuery specifies these classes by reference to Unicode
character properties, so equivalent behavior is obtained only with
a locale that follows the Unicode rules.
</para>
</listitem>
<listitem>
<para>
The SQL standard (not XQuery itself) attempts to cater for more
variants of <quote>newline</quote> than POSIX does. The
newline-sensitive matching options described above consider only
ASCII NL (<literal>\n</literal>) to be a newline, but SQL would have
us treat CR (<literal>\r</literal>), CRLF (<literal>\r\n</literal>)
(a Windows-style newline), and some Unicode-only characters like
LINE SEPARATOR (U+2028) as newlines as well.
Notably, <literal>.</literal> and <literal>\s</literal> should
count <literal>\r\n</literal> as one character not two according to
SQL.
</para>
</listitem>
<listitem>
<para>
Of the character-entry escapes described in
<xref linkend="posix-character-entry-escapes-table"/>,
XQuery supports only <literal>\n</literal>, <literal>\r</literal>,
and <literal>\t</literal>.
</para>
</listitem>
<listitem>
<para>
XQuery does not support
the <literal>[:<replaceable>name</replaceable>:]</literal> syntax
for character classes within bracket expressions.
</para>
</listitem>
<listitem>
<para>
XQuery does not have lookahead or lookbehind constraints,
nor any of the constraint escapes described in
<xref linkend="posix-constraint-escapes-table"/>.
</para>
</listitem>
<listitem>
<para>
The metasyntax forms described in <xref linkend="posix-metasyntax"/>
do not exist in XQuery.
</para>
</listitem>
<listitem>
<para>
The regular expression flag letters defined by XQuery are
related to but not the same as the option letters for POSIX
(<xref linkend="posix-embedded-options-table"/>). While the
<literal>i</literal> and <literal>q</literal> options behave the
same, others do not:
<itemizedlist>
<listitem>
<para>
XQuery's <literal>s</literal> (allow dot to match newline)
and <literal>m</literal> (allow <literal>^</literal>
and <literal>$</literal> to match at newlines) flags provide
access to the same behaviors as
POSIX's <literal>n</literal>, <literal>p</literal>
and <literal>w</literal> flags, but they
do <emphasis>not</emphasis> match the behavior of
POSIX's <literal>s</literal> and <literal>m</literal> flags.
Note in particular that dot-matches-newline is the default
behavior in POSIX but not XQuery.
</para>
</listitem>
<listitem>
<para>
XQuery's <literal>x</literal> (ignore whitespace in pattern) flag
is noticeably different from POSIX's expanded-mode flag.
POSIX's <literal>x</literal> flag also
allows <literal>#</literal> to begin a comment in the pattern,
and POSIX will not ignore a whitespace character after a
backslash.
</para>
</listitem>
</itemizedlist>
</para>
</listitem>
</itemizedlist>
</para>
</sect3>
</sect2>
</sect1>
<sect1 id="functions-formatting">
<title>Data Type Formatting Functions</title>
<indexterm>
<primary>formatting</primary>
</indexterm>
<para>
The <productname>PostgreSQL</productname> formatting functions
provide a powerful set of tools for converting various data types
(date/time, integer, floating point, numeric) to formatted strings
and for converting from formatted strings to specific data types.
<xref linkend="functions-formatting-table"/> lists them.
These functions all follow a common calling convention: the first
argument is the value to be formatted and the second argument is a
template that defines the output or input format.
</para>
<table id="functions-formatting-table">
<title>Formatting Functions</title>
<tgroup cols="1">
<thead>
<row>
<entry role="func_table_entry"><para role="func_signature">
Function
</para>
<para>
Description
</para>
<para>
Example(s)
</para></entry>
</row>
</thead>
<tbody>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>to_char</primary>
</indexterm>
<function>to_char</function> ( <type>timestamp</type>, <type>text</type> )
<returnvalue>text</returnvalue>
</para>
<para role="func_signature">
<function>to_char</function> ( <type>timestamp with time zone</type>, <type>text</type> )
<returnvalue>text</returnvalue>
</para>
<para>
Converts time stamp to string according to the given format.
</para>
<para>
<literal>to_char(timestamp '2002-04-20 17:31:12.66', 'HH12:MI:SS')</literal>
<returnvalue>05:31:12</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<function>to_char</function> ( <type>interval</type>, <type>text</type> )
<returnvalue>text</returnvalue>
</para>
<para>
Converts interval to string according to the given format.
</para>
<para>
<literal>to_char(interval '15h 2m 12s', 'HH24:MI:SS')</literal>
<returnvalue>15:02:12</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<function>to_char</function> ( <replaceable>numeric_type</replaceable>, <type>text</type> )
<returnvalue>text</returnvalue>
</para>
<para>
Converts number to string according to the given format; available
for <type>integer</type>, <type>bigint</type>, <type>numeric</type>,
<type>real</type>, <type>double precision</type>.
</para>
<para>
<literal>to_char(125, '999')</literal>
<returnvalue>125</returnvalue>
</para>
<para>
<literal>to_char(125.8::real, '999D9')</literal>
<returnvalue>125.8</returnvalue>
</para>
<para>
<literal>to_char(-125.8, '999D99S')</literal>
<returnvalue>125.80-</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>to_date</primary>
</indexterm>
<function>to_date</function> ( <type>text</type>, <type>text</type> )
<returnvalue>date</returnvalue>
</para>
<para>
Converts string to date according to the given format.
</para>
<para>
<literal>to_date('05 Dec 2000', 'DD Mon YYYY')</literal>
<returnvalue>2000-12-05</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>to_number</primary>
</indexterm>
<function>to_number</function> ( <type>text</type>, <type>text</type> )
<returnvalue>numeric</returnvalue>
</para>
<para>
Converts string to numeric according to the given format.
</para>
<para>
<literal>to_number('12,454.8-', '99G999D9S')</literal>
<returnvalue>-12454.8</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>to_timestamp</primary>
</indexterm>
<function>to_timestamp</function> ( <type>text</type>, <type>text</type> )
<returnvalue>timestamp with time zone</returnvalue>
</para>
<para>
Converts string to time stamp according to the given format.
(See also <function>to_timestamp(double precision)</function> in
<xref linkend="functions-datetime-table"/>.)
</para>
<para>
<literal>to_timestamp('05 Dec 2000', 'DD Mon YYYY')</literal>
<returnvalue>2000-12-05 00:00:00-05</returnvalue>
</para></entry>
</row>
</tbody>
</tgroup>
</table>
<tip>
<para>
<function>to_timestamp</function> and <function>to_date</function>
exist to handle input formats that cannot be converted by
simple casting. For most standard date/time formats, simply casting the
source string to the required data type works, and is much easier.
Similarly, <function>to_number</function> is unnecessary for standard numeric
representations.
</para>
</tip>
<para>
In a <function>to_char</function> output template string, there are certain
patterns that are recognized and replaced with appropriately-formatted
data based on the given value. Any text that is not a template pattern is
simply copied verbatim. Similarly, in an input template string (for the
other functions), template patterns identify the values to be supplied by
the input data string. If there are characters in the template string
that are not template patterns, the corresponding characters in the input
data string are simply skipped over (whether or not they are equal to the
template string characters).
</para>
<para>
<xref linkend="functions-formatting-datetime-table"/> shows the
template patterns available for formatting date and time values.
</para>
<table id="functions-formatting-datetime-table">
<title>Template Patterns for Date/Time Formatting</title>
<tgroup cols="2">
<thead>
<row>
<entry>Pattern</entry>
<entry>Description</entry>
</row>
</thead>
<tbody>
<row>
<entry><literal>HH</literal></entry>
<entry>hour of day (01–12)</entry>
</row>
<row>
<entry><literal>HH12</literal></entry>
<entry>hour of day (01–12)</entry>
</row>
<row>
<entry><literal>HH24</literal></entry>
<entry>hour of day (00–23)</entry>
</row>
<row>
<entry><literal>MI</literal></entry>
<entry>minute (00–59)</entry>
</row>
<row>
<entry><literal>SS</literal></entry>
<entry>second (00–59)</entry>
</row>
<row>
<entry><literal>MS</literal></entry>
<entry>millisecond (000–999)</entry>
</row>
<row>
<entry><literal>US</literal></entry>
<entry>microsecond (000000–999999)</entry>
</row>
<row>
<entry><literal>FF1</literal></entry>
<entry>tenth of second (0–9)</entry>
</row>
<row>
<entry><literal>FF2</literal></entry>
<entry>hundredth of second (00–99)</entry>
</row>
<row>
<entry><literal>FF3</literal></entry>
<entry>millisecond (000–999)</entry>
</row>
<row>
<entry><literal>FF4</literal></entry>
<entry>tenth of a millisecond (0000–9999)</entry>
</row>
<row>
<entry><literal>FF5</literal></entry>
<entry>hundredth of a millisecond (00000–99999)</entry>
</row>
<row>
<entry><literal>FF6</literal></entry>
<entry>microsecond (000000–999999)</entry>
</row>
<row>
<entry><literal>SSSS</literal>, <literal>SSSSS</literal></entry>
<entry>seconds past midnight (0–86399)</entry>
</row>
<row>
<entry><literal>AM</literal>, <literal>am</literal>,
<literal>PM</literal> or <literal>pm</literal></entry>
<entry>meridiem indicator (without periods)</entry>
</row>
<row>
<entry><literal>A.M.</literal>, <literal>a.m.</literal>,
<literal>P.M.</literal> or <literal>p.m.</literal></entry>
<entry>meridiem indicator (with periods)</entry>
</row>
<row>
<entry><literal>Y,YYY</literal></entry>
<entry>year (4 or more digits) with comma</entry>
</row>
<row>
<entry><literal>YYYY</literal></entry>
<entry>year (4 or more digits)</entry>
</row>
<row>
<entry><literal>YYY</literal></entry>
<entry>last 3 digits of year</entry>
</row>
<row>
<entry><literal>YY</literal></entry>
<entry>last 2 digits of year</entry>
</row>
<row>
<entry><literal>Y</literal></entry>
<entry>last digit of year</entry>
</row>
<row>
<entry><literal>IYYY</literal></entry>
<entry>ISO 8601 week-numbering year (4 or more digits)</entry>
</row>
<row>
<entry><literal>IYY</literal></entry>
<entry>last 3 digits of ISO 8601 week-numbering year</entry>
</row>
<row>
<entry><literal>IY</literal></entry>
<entry>last 2 digits of ISO 8601 week-numbering year</entry>
</row>
<row>
<entry><literal>I</literal></entry>
<entry>last digit of ISO 8601 week-numbering year</entry>
</row>
<row>
<entry><literal>BC</literal>, <literal>bc</literal>,
<literal>AD</literal> or <literal>ad</literal></entry>
<entry>era indicator (without periods)</entry>
</row>
<row>
<entry><literal>B.C.</literal>, <literal>b.c.</literal>,
<literal>A.D.</literal> or <literal>a.d.</literal></entry>
<entry>era indicator (with periods)</entry>
</row>
<row>
<entry><literal>MONTH</literal></entry>
<entry>full upper case month name (blank-padded to 9 chars)</entry>
</row>
<row>
<entry><literal>Month</literal></entry>
<entry>full capitalized month name (blank-padded to 9 chars)</entry>
</row>
<row>
<entry><literal>month</literal></entry>
<entry>full lower case month name (blank-padded to 9 chars)</entry>
</row>
<row>
<entry><literal>MON</literal></entry>
<entry>abbreviated upper case month name (3 chars in English, localized lengths vary)</entry>
</row>
<row>
<entry><literal>Mon</literal></entry>
<entry>abbreviated capitalized month name (3 chars in English, localized lengths vary)</entry>
</row>
<row>
<entry><literal>mon</literal></entry>
<entry>abbreviated lower case month name (3 chars in English, localized lengths vary)</entry>
</row>
<row>
<entry><literal>MM</literal></entry>
<entry>month number (01–12)</entry>
</row>
<row>
<entry><literal>DAY</literal></entry>
<entry>full upper case day name (blank-padded to 9 chars)</entry>
</row>
<row>
<entry><literal>Day</literal></entry>
<entry>full capitalized day name (blank-padded to 9 chars)</entry>
</row>
<row>
<entry><literal>day</literal></entry>
<entry>full lower case day name (blank-padded to 9 chars)</entry>
</row>
<row>
<entry><literal>DY</literal></entry>
<entry>abbreviated upper case day name (3 chars in English, localized lengths vary)</entry>
</row>
<row>
<entry><literal>Dy</literal></entry>
<entry>abbreviated capitalized day name (3 chars in English, localized lengths vary)</entry>
</row>
<row>
<entry><literal>dy</literal></entry>
<entry>abbreviated lower case day name (3 chars in English, localized lengths vary)</entry>
</row>
<row>
<entry><literal>DDD</literal></entry>
<entry>day of year (001–366)</entry>
</row>
<row>
<entry><literal>IDDD</literal></entry>
<entry>day of ISO 8601 week-numbering year (001–371; day 1 of the year is Monday of the first ISO week)</entry>
</row>
<row>
<entry><literal>DD</literal></entry>
<entry>day of month (01–31)</entry>
</row>
<row>
<entry><literal>D</literal></entry>
<entry>day of the week, Sunday (<literal>1</literal>) to Saturday (<literal>7</literal>)</entry>
</row>
<row>
<entry><literal>ID</literal></entry>
<entry>ISO 8601 day of the week, Monday (<literal>1</literal>) to Sunday (<literal>7</literal>)</entry>
</row>
<row>
<entry><literal>W</literal></entry>
<entry>week of month (1–5) (the first week starts on the first day of the month)</entry>
</row>
<row>
<entry><literal>WW</literal></entry>
<entry>week number of year (1–53) (the first week starts on the first day of the year)</entry>
</row>
<row>
<entry><literal>IW</literal></entry>
<entry>week number of ISO 8601 week-numbering year (01–53; the first Thursday of the year is in week 1)</entry>
</row>
<row>
<entry><literal>CC</literal></entry>
<entry>century (2 digits) (the twenty-first century starts on 2001-01-01)</entry>
</row>
<row>
<entry><literal>J</literal></entry>
<entry>Julian Date (integer days since November 24, 4714 BC at local
midnight; see <xref linkend="datetime-julian-dates"/>)</entry>
</row>
<row>
<entry><literal>Q</literal></entry>
<entry>quarter</entry>
</row>
<row>
<entry><literal>RM</literal></entry>
<entry>month in upper case Roman numerals (I–XII; I=January)</entry>
</row>
<row>
<entry><literal>rm</literal></entry>
<entry>month in lower case Roman numerals (i–xii; i=January)</entry>
</row>
<row>
<entry><literal>TZ</literal></entry>
<entry>upper case time-zone abbreviation
(only supported in <function>to_char</function>)</entry>
</row>
<row>
<entry><literal>tz</literal></entry>
<entry>lower case time-zone abbreviation
(only supported in <function>to_char</function>)</entry>
</row>
<row>
<entry><literal>TZH</literal></entry>
<entry>time-zone hours</entry>
</row>
<row>
<entry><literal>TZM</literal></entry>
<entry>time-zone minutes</entry>
</row>
<row>
<entry><literal>OF</literal></entry>
<entry>time-zone offset from UTC
(only supported in <function>to_char</function>)</entry>
</row>
</tbody>
</tgroup>
</table>
<para>
Modifiers can be applied to any template pattern to alter its
behavior. For example, <literal>FMMonth</literal>
is the <literal>Month</literal> pattern with the
<literal>FM</literal> modifier.
<xref linkend="functions-formatting-datetimemod-table"/> shows the
modifier patterns for date/time formatting.
</para>
<table id="functions-formatting-datetimemod-table">
<title>Template Pattern Modifiers for Date/Time Formatting</title>
<tgroup cols="3">
<thead>
<row>
<entry>Modifier</entry>
<entry>Description</entry>
<entry>Example</entry>
</row>
</thead>
<tbody>
<row>
<entry><literal>FM</literal> prefix</entry>
<entry>fill mode (suppress leading zeroes and padding blanks)</entry>
<entry><literal>FMMonth</literal></entry>
</row>
<row>
<entry><literal>TH</literal> suffix</entry>
<entry>upper case ordinal number suffix</entry>
<entry><literal>DDTH</literal>, e.g., <literal>12TH</literal></entry>
</row>
<row>
<entry><literal>th</literal> suffix</entry>
<entry>lower case ordinal number suffix</entry>
<entry><literal>DDth</literal>, e.g., <literal>12th</literal></entry>
</row>
<row>
<entry><literal>FX</literal> prefix</entry>
<entry>fixed format global option (see usage notes)</entry>
<entry><literal>FX Month DD Day</literal></entry>
</row>
<row>
<entry><literal>TM</literal> prefix</entry>
<entry>translation mode (use localized day and month names based on
<xref linkend="guc-lc-time"/>)</entry>
<entry><literal>TMMonth</literal></entry>
</row>
<row>
<entry><literal>SP</literal> suffix</entry>
<entry>spell mode (not implemented)</entry>
<entry><literal>DDSP</literal></entry>
</row>
</tbody>
</tgroup>
</table>
<para>
Usage notes for date/time formatting:
<itemizedlist>
<listitem>
<para>
<literal>FM</literal> suppresses leading zeroes and trailing blanks
that would otherwise be added to make the output of a pattern be
fixed-width. In <productname>PostgreSQL</productname>,
<literal>FM</literal> modifies only the next specification, while in
Oracle <literal>FM</literal> affects all subsequent
specifications, and repeated <literal>FM</literal> modifiers
toggle fill mode on and off.
</para>
</listitem>
<listitem>
<para>
<literal>TM</literal> suppresses trailing blanks whether or
not <literal>FM</literal> is specified.
</para>
</listitem>
<listitem>
<para>
<function>to_timestamp</function> and <function>to_date</function>
ignore letter case in the input; so for
example <literal>MON</literal>, <literal>Mon</literal>,
and <literal>mon</literal> all accept the same strings. When using
the <literal>TM</literal> modifier, case-folding is done according to
the rules of the function's input collation (see
<xref linkend="collation"/>).
</para>
</listitem>
<listitem>
<para>
<function>to_timestamp</function> and <function>to_date</function>
skip multiple blank spaces at the beginning of the input string and
around date and time values unless the <literal>FX</literal> option is used. For example,
<literal>to_timestamp(' 2000 JUN', 'YYYY MON')</literal> and
<literal>to_timestamp('2000 - JUN', 'YYYY-MON')</literal> work, but
<literal>to_timestamp('2000 JUN', 'FXYYYY MON')</literal> returns an error
because <function>to_timestamp</function> expects only a single space.
<literal>FX</literal> must be specified as the first item in
the template.
</para>
</listitem>
<listitem>
<para>
A separator (a space or non-letter/non-digit character) in the template string of
<function>to_timestamp</function> and <function>to_date</function>
matches any single separator in the input string or is skipped,
unless the <literal>FX</literal> option is used.
For example, <literal>to_timestamp('2000JUN', 'YYYY///MON')</literal> and
<literal>to_timestamp('2000/JUN', 'YYYY MON')</literal> work, but
<literal>to_timestamp('2000//JUN', 'YYYY/MON')</literal>
returns an error because the number of separators in the input string
exceeds the number of separators in the template.
</para>
<para>
If <literal>FX</literal> is specified, a separator in the template string
matches exactly one character in the input string. But note that the
input string character is not required to be the same as the separator from the template string.
For example, <literal>to_timestamp('2000/JUN', 'FXYYYY MON')</literal>
works, but <literal>to_timestamp('2000/JUN', 'FXYYYY MON')</literal>
returns an error because the second space in the template string consumes
the letter <literal>J</literal> from the input string.
</para>
</listitem>
<listitem>
<para>
A <literal>TZH</literal> template pattern can match a signed number.
Without the <literal>FX</literal> option, minus signs may be ambiguous,
and could be interpreted as a separator.
This ambiguity is resolved as follows: If the number of separators before
<literal>TZH</literal> in the template string is less than the number of
separators before the minus sign in the input string, the minus sign
is interpreted as part of <literal>TZH</literal>.
Otherwise, the minus sign is considered to be a separator between values.
For example, <literal>to_timestamp('2000 -10', 'YYYY TZH')</literal> matches
<literal>-10</literal> to <literal>TZH</literal>, but
<literal>to_timestamp('2000 -10', 'YYYY TZH')</literal>
matches <literal>10</literal> to <literal>TZH</literal>.
</para>
</listitem>
<listitem>
<para>
Ordinary text is allowed in <function>to_char</function>
templates and will be output literally. You can put a substring
in double quotes to force it to be interpreted as literal text
even if it contains template patterns. For example, in
<literal>'"Hello Year "YYYY'</literal>, the <literal>YYYY</literal>
will be replaced by the year data, but the single <literal>Y</literal> in <literal>Year</literal>
will not be.
In <function>to_date</function>, <function>to_number</function>,
and <function>to_timestamp</function>, literal text and double-quoted
strings result in skipping the number of characters contained in the
string; for example <literal>"XX"</literal> skips two input characters
(whether or not they are <literal>XX</literal>).
</para>
<tip>
<para>
Prior to <productname>PostgreSQL</productname> 12, it was possible to
skip arbitrary text in the input string using non-letter or non-digit
characters. For example,
<literal>to_timestamp('2000y6m1d', 'yyyy-MM-DD')</literal> used to
work. Now you can only use letter characters for this purpose. For example,
<literal>to_timestamp('2000y6m1d', 'yyyytMMtDDt')</literal> and
<literal>to_timestamp('2000y6m1d', 'yyyy"y"MM"m"DD"d"')</literal>
skip <literal>y</literal>, <literal>m</literal>, and
<literal>d</literal>.
</para>
</tip>
</listitem>
<listitem>
<para>
If you want to have a double quote in the output you must
precede it with a backslash, for example <literal>'\"YYYY
Month\"'</literal>. <!-- "" font-lock sanity :-) -->
Backslashes are not otherwise special outside of double-quoted
strings. Within a double-quoted string, a backslash causes the
next character to be taken literally, whatever it is (but this
has no special effect unless the next character is a double quote
or another backslash).
</para>
</listitem>
<listitem>
<para>
In <function>to_timestamp</function> and <function>to_date</function>,
if the year format specification is less than four digits, e.g.,
<literal>YYY</literal>, and the supplied year is less than four digits,
the year will be adjusted to be nearest to the year 2020, e.g.,
<literal>95</literal> becomes 1995.
</para>
</listitem>
<listitem>
<para>
In <function>to_timestamp</function> and <function>to_date</function>,
negative years are treated as signifying BC. If you write both a
negative year and an explicit <literal>BC</literal> field, you get AD
again. An input of year zero is treated as 1 BC.
</para>
</listitem>
<listitem>
<para>
In <function>to_timestamp</function> and <function>to_date</function>,
the <literal>YYYY</literal> conversion has a restriction when
processing years with more than 4 digits. You must
use some non-digit character or template after <literal>YYYY</literal>,
otherwise the year is always interpreted as 4 digits. For example
(with the year 20000):
<literal>to_date('200001131', 'YYYYMMDD')</literal> will be
interpreted as a 4-digit year; instead use a non-digit
separator after the year, like
<literal>to_date('20000-1131', 'YYYY-MMDD')</literal> or
<literal>to_date('20000Nov31', 'YYYYMonDD')</literal>.
</para>
</listitem>
<listitem>
<para>
In <function>to_timestamp</function> and <function>to_date</function>,
the <literal>CC</literal> (century) field is accepted but ignored
if there is a <literal>YYY</literal>, <literal>YYYY</literal> or
<literal>Y,YYY</literal> field. If <literal>CC</literal> is used with
<literal>YY</literal> or <literal>Y</literal> then the result is
computed as that year in the specified century. If the century is
specified but the year is not, the first year of the century
is assumed.
</para>
</listitem>
<listitem>
<para>
In <function>to_timestamp</function> and <function>to_date</function>,
weekday names or numbers (<literal>DAY</literal>, <literal>D</literal>,
and related field types) are accepted but are ignored for purposes of
computing the result. The same is true for quarter
(<literal>Q</literal>) fields.
</para>
</listitem>
<listitem>
<para>
In <function>to_timestamp</function> and <function>to_date</function>,
an ISO 8601 week-numbering date (as distinct from a Gregorian date)
can be specified in one of two ways:
<itemizedlist>
<listitem>
<para>
Year, week number, and weekday: for
example <literal>to_date('2006-42-4', 'IYYY-IW-ID')</literal>
returns the date <literal>2006-10-19</literal>.
If you omit the weekday it is assumed to be 1 (Monday).
</para>
</listitem>
<listitem>
<para>
Year and day of year: for example <literal>to_date('2006-291',
'IYYY-IDDD')</literal> also returns <literal>2006-10-19</literal>.
</para>
</listitem>
</itemizedlist>
</para>
<para>
Attempting to enter a date using a mixture of ISO 8601 week-numbering
fields and Gregorian date fields is nonsensical, and will cause an
error. In the context of an ISO 8601 week-numbering year, the
concept of a <quote>month</quote> or <quote>day of month</quote> has no
meaning. In the context of a Gregorian year, the ISO week has no
meaning.
</para>
<caution>
<para>
While <function>to_date</function> will reject a mixture of
Gregorian and ISO week-numbering date
fields, <function>to_char</function> will not, since output format
specifications like <literal>YYYY-MM-DD (IYYY-IDDD)</literal> can be
useful. But avoid writing something like <literal>IYYY-MM-DD</literal>;
that would yield surprising results near the start of the year.
(See <xref linkend="functions-datetime-extract"/> for more
information.)
</para>
</caution>
</listitem>
<listitem>
<para>
In <function>to_timestamp</function>, millisecond
(<literal>MS</literal>) or microsecond (<literal>US</literal>)
fields are used as the
seconds digits after the decimal point. For example
<literal>to_timestamp('12.3', 'SS.MS')</literal> is not 3 milliseconds,
but 300, because the conversion treats it as 12 + 0.3 seconds.
So, for the format <literal>SS.MS</literal>, the input values
<literal>12.3</literal>, <literal>12.30</literal>,
and <literal>12.300</literal> specify the
same number of milliseconds. To get three milliseconds, one must write
<literal>12.003</literal>, which the conversion treats as
12 + 0.003 = 12.003 seconds.
</para>
<para>
Here is a more
complex example:
<literal>to_timestamp('15:12:02.020.001230', 'HH24:MI:SS.MS.US')</literal>
is 15 hours, 12 minutes, and 2 seconds + 20 milliseconds +
1230 microseconds = 2.021230 seconds.
</para>
</listitem>
<listitem>
<para>
<function>to_char(..., 'ID')</function>'s day of the week numbering
matches the <function>extract(isodow from ...)</function> function, but
<function>to_char(..., 'D')</function>'s does not match
<function>extract(dow from ...)</function>'s day numbering.
</para>
</listitem>
<listitem>
<para>
<function>to_char(interval)</function> formats <literal>HH</literal> and
<literal>HH12</literal> as shown on a 12-hour clock, for example zero hours
and 36 hours both output as <literal>12</literal>, while <literal>HH24</literal>
outputs the full hour value, which can exceed 23 in
an <type>interval</type> value.
</para>
</listitem>
</itemizedlist>
</para>
<para>
<xref linkend="functions-formatting-numeric-table"/> shows the
template patterns available for formatting numeric values.
</para>
<table id="functions-formatting-numeric-table">
<title>Template Patterns for Numeric Formatting</title>
<tgroup cols="2">
<thead>
<row>
<entry>Pattern</entry>
<entry>Description</entry>
</row>
</thead>
<tbody>
<row>
<entry><literal>9</literal></entry>
<entry>digit position (can be dropped if insignificant)</entry>
</row>
<row>
<entry><literal>0</literal></entry>
<entry>digit position (will not be dropped, even if insignificant)</entry>
</row>
<row>
<entry><literal>.</literal> (period)</entry>
<entry>decimal point</entry>
</row>
<row>
<entry><literal>,</literal> (comma)</entry>
<entry>group (thousands) separator</entry>
</row>
<row>
<entry><literal>PR</literal></entry>
<entry>negative value in angle brackets</entry>
</row>
<row>
<entry><literal>S</literal></entry>
<entry>sign anchored to number (uses locale)</entry>
</row>
<row>
<entry><literal>L</literal></entry>
<entry>currency symbol (uses locale)</entry>
</row>
<row>
<entry><literal>D</literal></entry>
<entry>decimal point (uses locale)</entry>
</row>
<row>
<entry><literal>G</literal></entry>
<entry>group separator (uses locale)</entry>
</row>
<row>
<entry><literal>MI</literal></entry>
<entry>minus sign in specified position (if number < 0)</entry>
</row>
<row>
<entry><literal>PL</literal></entry>
<entry>plus sign in specified position (if number > 0)</entry>
</row>
<row>
<entry><literal>SG</literal></entry>
<entry>plus/minus sign in specified position</entry>
</row>
<row>
<entry><literal>RN</literal></entry>
<entry>Roman numeral (input between 1 and 3999)</entry>
</row>
<row>
<entry><literal>TH</literal> or <literal>th</literal></entry>
<entry>ordinal number suffix</entry>
</row>
<row>
<entry><literal>V</literal></entry>
<entry>shift specified number of digits (see notes)</entry>
</row>
<row>
<entry><literal>EEEE</literal></entry>
<entry>exponent for scientific notation</entry>
</row>
</tbody>
</tgroup>
</table>
<para>
Usage notes for numeric formatting:
<itemizedlist>
<listitem>
<para>
<literal>0</literal> specifies a digit position that will always be printed,
even if it contains a leading/trailing zero. <literal>9</literal> also
specifies a digit position, but if it is a leading zero then it will
be replaced by a space, while if it is a trailing zero and fill mode
is specified then it will be deleted. (For <function>to_number()</function>,
these two pattern characters are equivalent.)
</para>
</listitem>
<listitem>
<para>
The pattern characters <literal>S</literal>, <literal>L</literal>, <literal>D</literal>,
and <literal>G</literal> represent the sign, currency symbol, decimal point,
and thousands separator characters defined by the current locale
(see <xref linkend="guc-lc-monetary"/>
and <xref linkend="guc-lc-numeric"/>). The pattern characters period
and comma represent those exact characters, with the meanings of
decimal point and thousands separator, regardless of locale.
</para>
</listitem>
<listitem>
<para>
If no explicit provision is made for a sign
in <function>to_char()</function>'s pattern, one column will be reserved for
the sign, and it will be anchored to (appear just left of) the
number. If <literal>S</literal> appears just left of some <literal>9</literal>'s,
it will likewise be anchored to the number.
</para>
</listitem>
<listitem>
<para>
A sign formatted using <literal>SG</literal>, <literal>PL</literal>, or
<literal>MI</literal> is not anchored to
the number; for example,
<literal>to_char(-12, 'MI9999')</literal> produces <literal>'- 12'</literal>
but <literal>to_char(-12, 'S9999')</literal> produces <literal>' -12'</literal>.
(The Oracle implementation does not allow the use of
<literal>MI</literal> before <literal>9</literal>, but rather
requires that <literal>9</literal> precede
<literal>MI</literal>.)
</para>
</listitem>
<listitem>
<para>
<literal>TH</literal> does not convert values less than zero
and does not convert fractional numbers.
</para>
</listitem>
<listitem>
<para>
<literal>PL</literal>, <literal>SG</literal>, and
<literal>TH</literal> are <productname>PostgreSQL</productname>
extensions.
</para>
</listitem>
<listitem>
<para>
In <function>to_number</function>, if non-data template patterns such
as <literal>L</literal> or <literal>TH</literal> are used, the
corresponding number of input characters are skipped, whether or not
they match the template pattern, unless they are data characters
(that is, digits, sign, decimal point, or comma). For
example, <literal>TH</literal> would skip two non-data characters.
</para>
</listitem>
<listitem>
<para>
<literal>V</literal> with <function>to_char</function>
multiplies the input values by
<literal>10^<replaceable>n</replaceable></literal>, where
<replaceable>n</replaceable> is the number of digits following
<literal>V</literal>. <literal>V</literal> with
<function>to_number</function> divides in a similar manner.
<function>to_char</function> and <function>to_number</function>
do not support the use of
<literal>V</literal> combined with a decimal point
(e.g., <literal>99.9V99</literal> is not allowed).
</para>
</listitem>
<listitem>
<para>
<literal>EEEE</literal> (scientific notation) cannot be used in
combination with any of the other formatting patterns or
modifiers other than digit and decimal point patterns, and must be at the end of the format string
(e.g., <literal>9.99EEEE</literal> is a valid pattern).
</para>
</listitem>
</itemizedlist>
</para>
<para>
Certain modifiers can be applied to any template pattern to alter its
behavior. For example, <literal>FM99.99</literal>
is the <literal>99.99</literal> pattern with the
<literal>FM</literal> modifier.
<xref linkend="functions-formatting-numericmod-table"/> shows the
modifier patterns for numeric formatting.
</para>
<table id="functions-formatting-numericmod-table">
<title>Template Pattern Modifiers for Numeric Formatting</title>
<tgroup cols="3">
<thead>
<row>
<entry>Modifier</entry>
<entry>Description</entry>
<entry>Example</entry>
</row>
</thead>
<tbody>
<row>
<entry><literal>FM</literal> prefix</entry>
<entry>fill mode (suppress trailing zeroes and padding blanks)</entry>
<entry><literal>FM99.99</literal></entry>
</row>
<row>
<entry><literal>TH</literal> suffix</entry>
<entry>upper case ordinal number suffix</entry>
<entry><literal>999TH</literal></entry>
</row>
<row>
<entry><literal>th</literal> suffix</entry>
<entry>lower case ordinal number suffix</entry>
<entry><literal>999th</literal></entry>
</row>
</tbody>
</tgroup>
</table>
<para>
<xref linkend="functions-formatting-examples-table"/> shows some
examples of the use of the <function>to_char</function> function.
</para>
<table id="functions-formatting-examples-table">
<title><function>to_char</function> Examples</title>
<tgroup cols="2">
<thead>
<row>
<entry>Expression</entry>
<entry>Result</entry>
</row>
</thead>
<tbody>
<row>
<entry><literal>to_char(current_timestamp, 'Day, DD HH12:MI:SS')</literal></entry>
<entry><literal>'Tuesday , 06 05:39:18'</literal></entry>
</row>
<row>
<entry><literal>to_char(current_timestamp, 'FMDay, FMDD HH12:MI:SS')</literal></entry>
<entry><literal>'Tuesday, 6 05:39:18'</literal></entry>
</row>
<row>
<entry><literal>to_char(-0.1, '99.99')</literal></entry>
<entry><literal>' -.10'</literal></entry>
</row>
<row>
<entry><literal>to_char(-0.1, 'FM9.99')</literal></entry>
<entry><literal>'-.1'</literal></entry>
</row>
<row>
<entry><literal>to_char(-0.1, 'FM90.99')</literal></entry>
<entry><literal>'-0.1'</literal></entry>
</row>
<row>
<entry><literal>to_char(0.1, '0.9')</literal></entry>
<entry><literal>' 0.1'</literal></entry>
</row>
<row>
<entry><literal>to_char(12, '9990999.9')</literal></entry>
<entry><literal>' 0012.0'</literal></entry>
</row>
<row>
<entry><literal>to_char(12, 'FM9990999.9')</literal></entry>
<entry><literal>'0012.'</literal></entry>
</row>
<row>
<entry><literal>to_char(485, '999')</literal></entry>
<entry><literal>' 485'</literal></entry>
</row>
<row>
<entry><literal>to_char(-485, '999')</literal></entry>
<entry><literal>'-485'</literal></entry>
</row>
<row>
<entry><literal>to_char(485, '9 9 9')</literal></entry>
<entry><literal>' 4 8 5'</literal></entry>
</row>
<row>
<entry><literal>to_char(1485, '9,999')</literal></entry>
<entry><literal>' 1,485'</literal></entry>
</row>
<row>
<entry><literal>to_char(1485, '9G999')</literal></entry>
<entry><literal>' 1 485'</literal></entry>
</row>
<row>
<entry><literal>to_char(148.5, '999.999')</literal></entry>
<entry><literal>' 148.500'</literal></entry>
</row>
<row>
<entry><literal>to_char(148.5, 'FM999.999')</literal></entry>
<entry><literal>'148.5'</literal></entry>
</row>
<row>
<entry><literal>to_char(148.5, 'FM999.990')</literal></entry>
<entry><literal>'148.500'</literal></entry>
</row>
<row>
<entry><literal>to_char(148.5, '999D999')</literal></entry>
<entry><literal>' 148,500'</literal></entry>
</row>
<row>
<entry><literal>to_char(3148.5, '9G999D999')</literal></entry>
<entry><literal>' 3 148,500'</literal></entry>
</row>
<row>
<entry><literal>to_char(-485, '999S')</literal></entry>
<entry><literal>'485-'</literal></entry>
</row>
<row>
<entry><literal>to_char(-485, '999MI')</literal></entry>
<entry><literal>'485-'</literal></entry>
</row>
<row>
<entry><literal>to_char(485, '999MI')</literal></entry>
<entry><literal>'485 '</literal></entry>
</row>
<row>
<entry><literal>to_char(485, 'FM999MI')</literal></entry>
<entry><literal>'485'</literal></entry>
</row>
<row>
<entry><literal>to_char(485, 'PL999')</literal></entry>
<entry><literal>'+485'</literal></entry>
</row>
<row>
<entry><literal>to_char(485, 'SG999')</literal></entry>
<entry><literal>'+485'</literal></entry>
</row>
<row>
<entry><literal>to_char(-485, 'SG999')</literal></entry>
<entry><literal>'-485'</literal></entry>
</row>
<row>
<entry><literal>to_char(-485, '9SG99')</literal></entry>
<entry><literal>'4-85'</literal></entry>
</row>
<row>
<entry><literal>to_char(-485, '999PR')</literal></entry>
<entry><literal>'<485>'</literal></entry>
</row>
<row>
<entry><literal>to_char(485, 'L999')</literal></entry>
<entry><literal>'DM 485'</literal></entry>
</row>
<row>
<entry><literal>to_char(485, 'RN')</literal></entry>
<entry><literal>' CDLXXXV'</literal></entry>
</row>
<row>
<entry><literal>to_char(485, 'FMRN')</literal></entry>
<entry><literal>'CDLXXXV'</literal></entry>
</row>
<row>
<entry><literal>to_char(5.2, 'FMRN')</literal></entry>
<entry><literal>'V'</literal></entry>
</row>
<row>
<entry><literal>to_char(482, '999th')</literal></entry>
<entry><literal>' 482nd'</literal></entry>
</row>
<row>
<entry><literal>to_char(485, '"Good number:"999')</literal></entry>
<entry><literal>'Good number: 485'</literal></entry>
</row>
<row>
<entry><literal>to_char(485.8, '"Pre:"999" Post:" .999')</literal></entry>
<entry><literal>'Pre: 485 Post: .800'</literal></entry>
</row>
<row>
<entry><literal>to_char(12, '99V999')</literal></entry>
<entry><literal>' 12000'</literal></entry>
</row>
<row>
<entry><literal>to_char(12.4, '99V999')</literal></entry>
<entry><literal>' 12400'</literal></entry>
</row>
<row>
<entry><literal>to_char(12.45, '99V9')</literal></entry>
<entry><literal>' 125'</literal></entry>
</row>
<row>
<entry><literal>to_char(0.0004859, '9.99EEEE')</literal></entry>
<entry><literal>' 4.86e-04'</literal></entry>
</row>
</tbody>
</tgroup>
</table>
</sect1>
<sect1 id="functions-datetime">
<title>Date/Time Functions and Operators</title>
<para>
<xref linkend="functions-datetime-table"/> shows the available
functions for date/time value processing, with details appearing in
the following subsections. <xref
linkend="operators-datetime-table"/> illustrates the behaviors of
the basic arithmetic operators (<literal>+</literal>,
<literal>*</literal>, etc.). For formatting functions, refer to
<xref linkend="functions-formatting"/>. You should be familiar with
the background information on date/time data types from <xref
linkend="datatype-datetime"/>.
</para>
<para>
In addition, the usual comparison operators shown in
<xref linkend="functions-comparison-op-table"/> are available for the
date/time types. Dates and timestamps (with or without time zone) are
all comparable, while times (with or without time zone) and intervals
can only be compared to other values of the same data type. When
comparing a timestamp without time zone to a timestamp with time zone,
the former value is assumed to be given in the time zone specified by
the <xref linkend="guc-timezone"/> configuration parameter, and is
rotated to UTC for comparison to the latter value (which is already
in UTC internally). Similarly, a date value is assumed to represent
midnight in the <varname>TimeZone</varname> zone when comparing it
to a timestamp.
</para>
<para>
All the functions and operators described below that take <type>time</type> or <type>timestamp</type>
inputs actually come in two variants: one that takes <type>time with time zone</type> or <type>timestamp
with time zone</type>, and one that takes <type>time without time zone</type> or <type>timestamp without time zone</type>.
For brevity, these variants are not shown separately. Also, the
<literal>+</literal> and <literal>*</literal> operators come in commutative pairs (for
example both <type>date</type> <literal>+</literal> <type>integer</type>
and <type>integer</type> <literal>+</literal> <type>date</type>); we show
only one of each such pair.
</para>
<table id="operators-datetime-table">
<title>Date/Time Operators</title>
<tgroup cols="1">
<thead>
<row>
<entry role="func_table_entry"><para role="func_signature">
Operator
</para>
<para>
Description
</para>
<para>
Example(s)
</para></entry>
</row>
</thead>
<tbody>
<row>
<entry role="func_table_entry"><para role="func_signature">
<type>date</type> <literal>+</literal> <type>integer</type>
<returnvalue>date</returnvalue>
</para>
<para>
Add a number of days to a date
</para>
<para>
<literal>date '2001-09-28' + 7</literal>
<returnvalue>2001-10-05</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<type>date</type> <literal>+</literal> <type>interval</type>
<returnvalue>timestamp</returnvalue>
</para>
<para>
Add an interval to a date
</para>
<para>
<literal>date '2001-09-28' + interval '1 hour'</literal>
<returnvalue>2001-09-28 01:00:00</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<type>date</type> <literal>+</literal> <type>time</type>
<returnvalue>timestamp</returnvalue>
</para>
<para>
Add a time-of-day to a date
</para>
<para>
<literal>date '2001-09-28' + time '03:00'</literal>
<returnvalue>2001-09-28 03:00:00</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<type>interval</type> <literal>+</literal> <type>interval</type>
<returnvalue>interval</returnvalue>
</para>
<para>
Add intervals
</para>
<para>
<literal>interval '1 day' + interval '1 hour'</literal>
<returnvalue>1 day 01:00:00</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<type>timestamp</type> <literal>+</literal> <type>interval</type>
<returnvalue>timestamp</returnvalue>
</para>
<para>
Add an interval to a timestamp
</para>
<para>
<literal>timestamp '2001-09-28 01:00' + interval '23 hours'</literal>
<returnvalue>2001-09-29 00:00:00</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<type>time</type> <literal>+</literal> <type>interval</type>
<returnvalue>time</returnvalue>
</para>
<para>
Add an interval to a time
</para>
<para>
<literal>time '01:00' + interval '3 hours'</literal>
<returnvalue>04:00:00</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<literal>-</literal> <type>interval</type>
<returnvalue>interval</returnvalue>
</para>
<para>
Negate an interval
</para>
<para>
<literal>- interval '23 hours'</literal>
<returnvalue>-23:00:00</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<type>date</type> <literal>-</literal> <type>date</type>
<returnvalue>integer</returnvalue>
</para>
<para>
Subtract dates, producing the number of days elapsed
</para>
<para>
<literal>date '2001-10-01' - date '2001-09-28'</literal>
<returnvalue>3</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<type>date</type> <literal>-</literal> <type>integer</type>
<returnvalue>date</returnvalue>
</para>
<para>
Subtract a number of days from a date
</para>
<para>
<literal>date '2001-10-01' - 7</literal>
<returnvalue>2001-09-24</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<type>date</type> <literal>-</literal> <type>interval</type>
<returnvalue>timestamp</returnvalue>
</para>
<para>
Subtract an interval from a date
</para>
<para>
<literal>date '2001-09-28' - interval '1 hour'</literal>
<returnvalue>2001-09-27 23:00:00</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<type>time</type> <literal>-</literal> <type>time</type>
<returnvalue>interval</returnvalue>
</para>
<para>
Subtract times
</para>
<para>
<literal>time '05:00' - time '03:00'</literal>
<returnvalue>02:00:00</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<type>time</type> <literal>-</literal> <type>interval</type>
<returnvalue>time</returnvalue>
</para>
<para>
Subtract an interval from a time
</para>
<para>
<literal>time '05:00' - interval '2 hours'</literal>
<returnvalue>03:00:00</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<type>timestamp</type> <literal>-</literal> <type>interval</type>
<returnvalue>timestamp</returnvalue>
</para>
<para>
Subtract an interval from a timestamp
</para>
<para>
<literal>timestamp '2001-09-28 23:00' - interval '23 hours'</literal>
<returnvalue>2001-09-28 00:00:00</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<type>interval</type> <literal>-</literal> <type>interval</type>
<returnvalue>interval</returnvalue>
</para>
<para>
Subtract intervals
</para>
<para>
<literal>interval '1 day' - interval '1 hour'</literal>
<returnvalue>1 day -01:00:00</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<type>timestamp</type> <literal>-</literal> <type>timestamp</type>
<returnvalue>interval</returnvalue>
</para>
<para>
Subtract timestamps (converting 24-hour intervals into days,
similarly to <function>justify_hours()</function>)
</para>
<para>
<literal>timestamp '2001-09-29 03:00' - timestamp '2001-07-27 12:00'</literal>
<returnvalue>63 days 15:00:00</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<type>interval</type> <literal>*</literal> <type>double precision</type>
<returnvalue>interval</returnvalue>
</para>
<para>
Multiply an interval by a scalar
</para>
<para>
<literal>interval '1 second' * 900</literal>
<returnvalue>00:15:00</returnvalue>
</para>
<para>
<literal>interval '1 day' * 21</literal>
<returnvalue>21 days</returnvalue>
</para>
<para>
<literal>interval '1 hour' * 3.5</literal>
<returnvalue>03:30:00</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<type>interval</type> <literal>/</literal> <type>double precision</type>
<returnvalue>interval</returnvalue>
</para>
<para>
Divide an interval by a scalar
</para>
<para>
<literal>interval '1 hour' / 1.5</literal>
<returnvalue>00:40:00</returnvalue>
</para></entry>
</row>
</tbody>
</tgroup>
</table>
<table id="functions-datetime-table">
<title>Date/Time Functions</title>
<tgroup cols="1">
<thead>
<row>
<entry role="func_table_entry"><para role="func_signature">
Function
</para>
<para>
Description
</para>
<para>
Example(s)
</para></entry>
</row>
</thead>
<tbody>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>age</primary>
</indexterm>
<function>age</function> ( <type>timestamp</type>, <type>timestamp</type> )
<returnvalue>interval</returnvalue>
</para>
<para>
Subtract arguments, producing a <quote>symbolic</quote> result that
uses years and months, rather than just days
</para>
<para>
<literal>age(timestamp '2001-04-10', timestamp '1957-06-13')</literal>
<returnvalue>43 years 9 mons 27 days</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<function>age</function> ( <type>timestamp</type> )
<returnvalue>interval</returnvalue>
</para>
<para>
Subtract argument from <function>current_date</function> (at midnight)
</para>
<para>
<literal>age(timestamp '1957-06-13')</literal>
<returnvalue>62 years 6 mons 10 days</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>clock_timestamp</primary>
</indexterm>
<function>clock_timestamp</function> ( )
<returnvalue>timestamp with time zone</returnvalue>
</para>
<para>
Current date and time (changes during statement execution);
see <xref linkend="functions-datetime-current"/>
</para>
<para>
<literal>clock_timestamp()</literal>
<returnvalue>2019-12-23 14:39:53.662522-05</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>current_date</primary>
</indexterm>
<function>current_date</function>
<returnvalue>date</returnvalue>
</para>
<para>
Current date; see <xref linkend="functions-datetime-current"/>
</para>
<para>
<literal>current_date</literal>
<returnvalue>2019-12-23</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>current_time</primary>
</indexterm>
<function>current_time</function>
<returnvalue>time with time zone</returnvalue>
</para>
<para>
Current time of day; see <xref linkend="functions-datetime-current"/>
</para>
<para>
<literal>current_time</literal>
<returnvalue>14:39:53.662522-05</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<function>current_time</function> ( <type>integer</type> )
<returnvalue>time with time zone</returnvalue>
</para>
<para>
Current time of day, with limited precision;
see <xref linkend="functions-datetime-current"/>
</para>
<para>
<literal>current_time(2)</literal>
<returnvalue>14:39:53.66-05</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>current_timestamp</primary>
</indexterm>
<function>current_timestamp</function>
<returnvalue>timestamp with time zone</returnvalue>
</para>
<para>
Current date and time (start of current transaction);
see <xref linkend="functions-datetime-current"/>
</para>
<para>
<literal>current_timestamp</literal>
<returnvalue>2019-12-23 14:39:53.662522-05</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<function>current_timestamp</function> ( <type>integer</type> )
<returnvalue>timestamp with time zone</returnvalue>
</para>
<para>
Current date and time (start of current transaction), with limited precision;
see <xref linkend="functions-datetime-current"/>
</para>
<para>
<literal>current_timestamp(0)</literal>
<returnvalue>2019-12-23 14:39:53-05</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<function>date_bin</function> ( <type>interval</type>, <type>timestamp</type>, <type>timestamp</type> )
<returnvalue>timestamp</returnvalue>
</para>
<para>
Bin input into specified interval aligned with specified origin; see <xref linkend="functions-datetime-bin"/>
</para>
<para>
<literal>date_bin('15 minutes', timestamp '2001-02-16 20:38:40', timestamp '2001-02-16 20:05:00')</literal>
<returnvalue>2001-02-16 20:35:00</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>date_part</primary>
</indexterm>
<function>date_part</function> ( <type>text</type>, <type>timestamp</type> )
<returnvalue>double precision</returnvalue>
</para>
<para>
Get timestamp subfield (equivalent to <function>extract</function>);
see <xref linkend="functions-datetime-extract"/>
</para>
<para>
<literal>date_part('hour', timestamp '2001-02-16 20:38:40')</literal>
<returnvalue>20</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<function>date_part</function> ( <type>text</type>, <type>interval</type> )
<returnvalue>double precision</returnvalue>
</para>
<para>
Get interval subfield (equivalent to <function>extract</function>);
see <xref linkend="functions-datetime-extract"/>
</para>
<para>
<literal>date_part('month', interval '2 years 3 months')</literal>
<returnvalue>3</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>date_trunc</primary>
</indexterm>
<function>date_trunc</function> ( <type>text</type>, <type>timestamp</type> )
<returnvalue>timestamp</returnvalue>
</para>
<para>
Truncate to specified precision; see <xref linkend="functions-datetime-trunc"/>
</para>
<para>
<literal>date_trunc('hour', timestamp '2001-02-16 20:38:40')</literal>
<returnvalue>2001-02-16 20:00:00</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<function>date_trunc</function> ( <type>text</type>, <type>timestamp with time zone</type>, <type>text</type> )
<returnvalue>timestamp with time zone</returnvalue>
</para>
<para>
Truncate to specified precision in the specified time zone; see
<xref linkend="functions-datetime-trunc"/>
</para>
<para>
<literal>date_trunc('day', timestamptz '2001-02-16 20:38:40+00', 'Australia/Sydney')</literal>
<returnvalue>2001-02-16 13:00:00+00</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<function>date_trunc</function> ( <type>text</type>, <type>interval</type> )
<returnvalue>interval</returnvalue>
</para>
<para>
Truncate to specified precision; see
<xref linkend="functions-datetime-trunc"/>
</para>
<para>
<literal>date_trunc('hour', interval '2 days 3 hours 40 minutes')</literal>
<returnvalue>2 days 03:00:00</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>extract</primary>
</indexterm>
<function>extract</function> ( <parameter>field</parameter> <literal>from</literal> <type>timestamp</type> )
<returnvalue>numeric</returnvalue>
</para>
<para>
Get timestamp subfield; see <xref linkend="functions-datetime-extract"/>
</para>
<para>
<literal>extract(hour from timestamp '2001-02-16 20:38:40')</literal>
<returnvalue>20</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<function>extract</function> ( <parameter>field</parameter> <literal>from</literal> <type>interval</type> )
<returnvalue>numeric</returnvalue>
</para>
<para>
Get interval subfield; see <xref linkend="functions-datetime-extract"/>
</para>
<para>
<literal>extract(month from interval '2 years 3 months')</literal>
<returnvalue>3</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>isfinite</primary>
</indexterm>
<function>isfinite</function> ( <type>date</type> )
<returnvalue>boolean</returnvalue>
</para>
<para>
Test for finite date (not +/-infinity)
</para>
<para>
<literal>isfinite(date '2001-02-16')</literal>
<returnvalue>true</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<function>isfinite</function> ( <type>timestamp</type> )
<returnvalue>boolean</returnvalue>
</para>
<para>
Test for finite timestamp (not +/-infinity)
</para>
<para>
<literal>isfinite(timestamp 'infinity')</literal>
<returnvalue>false</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<function>isfinite</function> ( <type>interval</type> )
<returnvalue>boolean</returnvalue>
</para>
<para>
Test for finite interval (currently always true)
</para>
<para>
<literal>isfinite(interval '4 hours')</literal>
<returnvalue>true</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>justify_days</primary>
</indexterm>
<function>justify_days</function> ( <type>interval</type> )
<returnvalue>interval</returnvalue>
</para>
<para>
Adjust interval so 30-day time periods are represented as months
</para>
<para>
<literal>justify_days(interval '35 days')</literal>
<returnvalue>1 mon 5 days</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>justify_hours</primary>
</indexterm>
<function>justify_hours</function> ( <type>interval</type> )
<returnvalue>interval</returnvalue>
</para>
<para>
Adjust interval so 24-hour time periods are represented as days
</para>
<para>
<literal>justify_hours(interval '27 hours')</literal>
<returnvalue>1 day 03:00:00</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>justify_interval</primary>
</indexterm>
<function>justify_interval</function> ( <type>interval</type> )
<returnvalue>interval</returnvalue>
</para>
<para>
Adjust interval using <function>justify_days</function>
and <function>justify_hours</function>, with additional sign
adjustments
</para>
<para>
<literal>justify_interval(interval '1 mon -1 hour')</literal>
<returnvalue>29 days 23:00:00</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>localtime</primary>
</indexterm>
<function>localtime</function>
<returnvalue>time</returnvalue>
</para>
<para>
Current time of day;
see <xref linkend="functions-datetime-current"/>
</para>
<para>
<literal>localtime</literal>
<returnvalue>14:39:53.662522</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<function>localtime</function> ( <type>integer</type> )
<returnvalue>time</returnvalue>
</para>
<para>
Current time of day, with limited precision;
see <xref linkend="functions-datetime-current"/>
</para>
<para>
<literal>localtime(0)</literal>
<returnvalue>14:39:53</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>localtimestamp</primary>
</indexterm>
<function>localtimestamp</function>
<returnvalue>timestamp</returnvalue>
</para>
<para>
Current date and time (start of current transaction);
see <xref linkend="functions-datetime-current"/>
</para>
<para>
<literal>localtimestamp</literal>
<returnvalue>2019-12-23 14:39:53.662522</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<function>localtimestamp</function> ( <type>integer</type> )
<returnvalue>timestamp</returnvalue>
</para>
<para>
Current date and time (start of current
transaction), with limited precision;
see <xref linkend="functions-datetime-current"/>
</para>
<para>
<literal>localtimestamp(2)</literal>
<returnvalue>2019-12-23 14:39:53.66</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>make_date</primary>
</indexterm>
<function>make_date</function> ( <parameter>year</parameter> <type>int</type>,
<parameter>month</parameter> <type>int</type>,
<parameter>day</parameter> <type>int</type> )
<returnvalue>date</returnvalue>
</para>
<para>
Create date from year, month and day fields
(negative years signify BC)
</para>
<para>
<literal>make_date(2013, 7, 15)</literal>
<returnvalue>2013-07-15</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature"><indexterm>
<primary>make_interval</primary>
</indexterm>
<function>make_interval</function> ( <optional> <parameter>years</parameter> <type>int</type>
<optional>, <parameter>months</parameter> <type>int</type>
<optional>, <parameter>weeks</parameter> <type>int</type>
<optional>, <parameter>days</parameter> <type>int</type>
<optional>, <parameter>hours</parameter> <type>int</type>
<optional>, <parameter>mins</parameter> <type>int</type>
<optional>, <parameter>secs</parameter> <type>double precision</type>
</optional></optional></optional></optional></optional></optional></optional> )
<returnvalue>interval</returnvalue>
</para>
<para>
Create interval from years, months, weeks, days, hours, minutes and
seconds fields, each of which can default to zero
</para>
<para>
<literal>make_interval(days => 10)</literal>
<returnvalue>10 days</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>make_time</primary>
</indexterm>
<function>make_time</function> ( <parameter>hour</parameter> <type>int</type>,
<parameter>min</parameter> <type>int</type>,
<parameter>sec</parameter> <type>double precision</type> )
<returnvalue>time</returnvalue>
</para>
<para>
Create time from hour, minute and seconds fields
</para>
<para>
<literal>make_time(8, 15, 23.5)</literal>
<returnvalue>08:15:23.5</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>make_timestamp</primary>
</indexterm>
<function>make_timestamp</function> ( <parameter>year</parameter> <type>int</type>,
<parameter>month</parameter> <type>int</type>,
<parameter>day</parameter> <type>int</type>,
<parameter>hour</parameter> <type>int</type>,
<parameter>min</parameter> <type>int</type>,
<parameter>sec</parameter> <type>double precision</type> )
<returnvalue>timestamp</returnvalue>
</para>
<para>
Create timestamp from year, month, day, hour, minute and seconds fields
(negative years signify BC)
</para>
<para>
<literal>make_timestamp(2013, 7, 15, 8, 15, 23.5)</literal>
<returnvalue>2013-07-15 08:15:23.5</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>make_timestamptz</primary>
</indexterm>
<function>make_timestamptz</function> ( <parameter>year</parameter> <type>int</type>,
<parameter>month</parameter> <type>int</type>,
<parameter>day</parameter> <type>int</type>,
<parameter>hour</parameter> <type>int</type>,
<parameter>min</parameter> <type>int</type>,
<parameter>sec</parameter> <type>double precision</type>
<optional>, <parameter>timezone</parameter> <type>text</type> </optional> )
<returnvalue>timestamp with time zone</returnvalue>
</para>
<para>
Create timestamp with time zone from year, month, day, hour, minute
and seconds fields (negative years signify BC).
If <parameter>timezone</parameter> is not
specified, the current time zone is used; the examples assume the
session time zone is <literal>Europe/London</literal>
</para>
<para>
<literal>make_timestamptz(2013, 7, 15, 8, 15, 23.5)</literal>
<returnvalue>2013-07-15 08:15:23.5+01</returnvalue>
</para>
<para>
<literal>make_timestamptz(2013, 7, 15, 8, 15, 23.5, 'America/New_York')</literal>
<returnvalue>2013-07-15 13:15:23.5+01</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>now</primary>
</indexterm>
<function>now</function> ( )
<returnvalue>timestamp with time zone</returnvalue>
</para>
<para>
Current date and time (start of current transaction);
see <xref linkend="functions-datetime-current"/>
</para>
<para>
<literal>now()</literal>
<returnvalue>2019-12-23 14:39:53.662522-05</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>statement_timestamp</primary>
</indexterm>
<function>statement_timestamp</function> ( )
<returnvalue>timestamp with time zone</returnvalue>
</para>
<para>
Current date and time (start of current statement);
see <xref linkend="functions-datetime-current"/>
</para>
<para>
<literal>statement_timestamp()</literal>
<returnvalue>2019-12-23 14:39:53.662522-05</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>timeofday</primary>
</indexterm>
<function>timeofday</function> ( )
<returnvalue>text</returnvalue>
</para>
<para>
Current date and time
(like <function>clock_timestamp</function>, but as a <type>text</type> string);
see <xref linkend="functions-datetime-current"/>
</para>
<para>
<literal>timeofday()</literal>
<returnvalue>Mon Dec 23 14:39:53.662522 2019 EST</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>transaction_timestamp</primary>
</indexterm>
<function>transaction_timestamp</function> ( )
<returnvalue>timestamp with time zone</returnvalue>
</para>
<para>
Current date and time (start of current transaction);
see <xref linkend="functions-datetime-current"/>
</para>
<para>
<literal>transaction_timestamp()</literal>
<returnvalue>2019-12-23 14:39:53.662522-05</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>to_timestamp</primary>
</indexterm>
<function>to_timestamp</function> ( <type>double precision</type> )
<returnvalue>timestamp with time zone</returnvalue>
</para>
<para>
Convert Unix epoch (seconds since 1970-01-01 00:00:00+00) to
timestamp with time zone
</para>
<para>
<literal>to_timestamp(1284352323)</literal>
<returnvalue>2010-09-13 04:32:03+00</returnvalue>
</para></entry>
</row>
</tbody>
</tgroup>
</table>
<para>
<indexterm>
<primary>OVERLAPS</primary>
</indexterm>
In addition to these functions, the SQL <literal>OVERLAPS</literal> operator is
supported:
<synopsis>
(<replaceable>start1</replaceable>, <replaceable>end1</replaceable>) OVERLAPS (<replaceable>start2</replaceable>, <replaceable>end2</replaceable>)
(<replaceable>start1</replaceable>, <replaceable>length1</replaceable>) OVERLAPS (<replaceable>start2</replaceable>, <replaceable>length2</replaceable>)
</synopsis>
This expression yields true when two time periods (defined by their
endpoints) overlap, false when they do not overlap. The endpoints
can be specified as pairs of dates, times, or time stamps; or as
a date, time, or time stamp followed by an interval. When a pair
of values is provided, either the start or the end can be written
first; <literal>OVERLAPS</literal> automatically takes the earlier value
of the pair as the start. Each time period is considered to
represent the half-open interval <replaceable>start</replaceable> <literal><=</literal>
<replaceable>time</replaceable> <literal><</literal> <replaceable>end</replaceable>, unless
<replaceable>start</replaceable> and <replaceable>end</replaceable> are equal in which case it
represents that single time instant. This means for instance that two
time periods with only an endpoint in common do not overlap.
</para>
<screen>
SELECT (DATE '2001-02-16', DATE '2001-12-21') OVERLAPS
(DATE '2001-10-30', DATE '2002-10-30');
<lineannotation>Result: </lineannotation><computeroutput>true</computeroutput>
SELECT (DATE '2001-02-16', INTERVAL '100 days') OVERLAPS
(DATE '2001-10-30', DATE '2002-10-30');
<lineannotation>Result: </lineannotation><computeroutput>false</computeroutput>
SELECT (DATE '2001-10-29', DATE '2001-10-30') OVERLAPS
(DATE '2001-10-30', DATE '2001-10-31');
<lineannotation>Result: </lineannotation><computeroutput>false</computeroutput>
SELECT (DATE '2001-10-30', DATE '2001-10-30') OVERLAPS
(DATE '2001-10-30', DATE '2001-10-31');
<lineannotation>Result: </lineannotation><computeroutput>true</computeroutput>
</screen>
<para>
When adding an <type>interval</type> value to (or subtracting an
<type>interval</type> value from) a <type>timestamp with time zone</type>
value, the days component advances or decrements the date of the
<type>timestamp with time zone</type> by the indicated number of days,
keeping the time of day the same.
Across daylight saving time changes (when the session time zone is set to a
time zone that recognizes DST), this means <literal>interval '1 day'</literal>
does not necessarily equal <literal>interval '24 hours'</literal>.
For example, with the session time zone set
to <literal>America/Denver</literal>:
<screen>
SELECT timestamp with time zone '2005-04-02 12:00:00-07' + interval '1 day';
<lineannotation>Result: </lineannotation><computeroutput>2005-04-03 12:00:00-06</computeroutput>
SELECT timestamp with time zone '2005-04-02 12:00:00-07' + interval '24 hours';
<lineannotation>Result: </lineannotation><computeroutput>2005-04-03 13:00:00-06</computeroutput>
</screen>
This happens because an hour was skipped due to a change in daylight saving
time at <literal>2005-04-03 02:00:00</literal> in time zone
<literal>America/Denver</literal>.
</para>
<para>
Note there can be ambiguity in the <literal>months</literal> field returned by
<function>age</function> because different months have different numbers of
days. <productname>PostgreSQL</productname>'s approach uses the month from the
earlier of the two dates when calculating partial months. For example,
<literal>age('2004-06-01', '2004-04-30')</literal> uses April to yield
<literal>1 mon 1 day</literal>, while using May would yield <literal>1 mon 2
days</literal> because May has 31 days, while April has only 30.
</para>
<para>
Subtraction of dates and timestamps can also be complex. One conceptually
simple way to perform subtraction is to convert each value to a number
of seconds using <literal>EXTRACT(EPOCH FROM ...)</literal>, then subtract the
results; this produces the
number of <emphasis>seconds</emphasis> between the two values. This will adjust
for the number of days in each month, timezone changes, and daylight
saving time adjustments. Subtraction of date or timestamp
values with the <quote><literal>-</literal></quote> operator
returns the number of days (24-hours) and hours/minutes/seconds
between the values, making the same adjustments. The <function>age</function>
function returns years, months, days, and hours/minutes/seconds,
performing field-by-field subtraction and then adjusting for negative
field values. The following queries illustrate the differences in these
approaches. The sample results were produced with <literal>timezone
= 'US/Eastern'</literal>; there is a daylight saving time change between the
two dates used:
</para>
<screen>
SELECT EXTRACT(EPOCH FROM timestamptz '2013-07-01 12:00:00') -
EXTRACT(EPOCH FROM timestamptz '2013-03-01 12:00:00');
<lineannotation>Result: </lineannotation><computeroutput>10537200</computeroutput>
SELECT (EXTRACT(EPOCH FROM timestamptz '2013-07-01 12:00:00') -
EXTRACT(EPOCH FROM timestamptz '2013-03-01 12:00:00'))
/ 60 / 60 / 24;
<lineannotation>Result: </lineannotation><computeroutput>121.958333333333</computeroutput>
SELECT timestamptz '2013-07-01 12:00:00' - timestamptz '2013-03-01 12:00:00';
<lineannotation>Result: </lineannotation><computeroutput>121 days 23:00:00</computeroutput>
SELECT age(timestamptz '2013-07-01 12:00:00', timestamptz '2013-03-01 12:00:00');
<lineannotation>Result: </lineannotation><computeroutput>4 mons</computeroutput>
</screen>
<sect2 id="functions-datetime-extract">
<title><function>EXTRACT</function>, <function>date_part</function></title>
<indexterm>
<primary>date_part</primary>
</indexterm>
<indexterm>
<primary>extract</primary>
</indexterm>
<synopsis>
EXTRACT(<replaceable>field</replaceable> FROM <replaceable>source</replaceable>)
</synopsis>
<para>
The <function>extract</function> function retrieves subfields
such as year or hour from date/time values.
<replaceable>source</replaceable> must be a value expression of
type <type>timestamp</type>, <type>time</type>, or <type>interval</type>.
(Expressions of type <type>date</type> are
cast to <type>timestamp</type> and can therefore be used as
well.) <replaceable>field</replaceable> is an identifier or
string that selects what field to extract from the source value.
The <function>extract</function> function returns values of type
<type>numeric</type>.
The following are valid field names:
<!-- alphabetical -->
<variablelist>
<varlistentry>
<term><literal>century</literal></term>
<listitem>
<para>
The century
</para>
<screen>
SELECT EXTRACT(CENTURY FROM TIMESTAMP '2000-12-16 12:21:13');
<lineannotation>Result: </lineannotation><computeroutput>20</computeroutput>
SELECT EXTRACT(CENTURY FROM TIMESTAMP '2001-02-16 20:38:40');
<lineannotation>Result: </lineannotation><computeroutput>21</computeroutput>
</screen>
<para>
The first century starts at 0001-01-01 00:00:00 AD, although
they did not know it at the time. This definition applies to all
Gregorian calendar countries. There is no century number 0,
you go from -1 century to 1 century.
If you disagree with this, please write your complaint to:
Pope, Cathedral Saint-Peter of Roma, Vatican.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>day</literal></term>
<listitem>
<para>
For <type>timestamp</type> values, the day (of the month) field
(1–31) ; for <type>interval</type> values, the number of days
</para>
<screen>
SELECT EXTRACT(DAY FROM TIMESTAMP '2001-02-16 20:38:40');
<lineannotation>Result: </lineannotation><computeroutput>16</computeroutput>
SELECT EXTRACT(DAY FROM INTERVAL '40 days 1 minute');
<lineannotation>Result: </lineannotation><computeroutput>40</computeroutput>
</screen>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>decade</literal></term>
<listitem>
<para>
The year field divided by 10
</para>
<screen>
SELECT EXTRACT(DECADE FROM TIMESTAMP '2001-02-16 20:38:40');
<lineannotation>Result: </lineannotation><computeroutput>200</computeroutput>
</screen>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>dow</literal></term>
<listitem>
<para>
The day of the week as Sunday (<literal>0</literal>) to
Saturday (<literal>6</literal>)
</para>
<screen>
SELECT EXTRACT(DOW FROM TIMESTAMP '2001-02-16 20:38:40');
<lineannotation>Result: </lineannotation><computeroutput>5</computeroutput>
</screen>
<para>
Note that <function>extract</function>'s day of the week numbering
differs from that of the <function>to_char(...,
'D')</function> function.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>doy</literal></term>
<listitem>
<para>
The day of the year (1–365/366)
</para>
<screen>
SELECT EXTRACT(DOY FROM TIMESTAMP '2001-02-16 20:38:40');
<lineannotation>Result: </lineannotation><computeroutput>47</computeroutput>
</screen>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>epoch</literal></term>
<listitem>
<para>
For <type>timestamp with time zone</type> values, the
number of seconds since 1970-01-01 00:00:00 UTC (negative for
timestamps before that);
for <type>date</type> and <type>timestamp</type> values, the
nominal number of seconds since 1970-01-01 00:00:00,
without regard to timezone or daylight-savings rules;
for <type>interval</type> values, the total number
of seconds in the interval
</para>
<screen>
SELECT EXTRACT(EPOCH FROM TIMESTAMP WITH TIME ZONE '2001-02-16 20:38:40.12-08');
<lineannotation>Result: </lineannotation><computeroutput>982384720.12</computeroutput>
SELECT EXTRACT(EPOCH FROM TIMESTAMP '2001-02-16 20:38:40.12');
<lineannotation>Result: </lineannotation><computeroutput>982355920.12</computeroutput>
SELECT EXTRACT(EPOCH FROM INTERVAL '5 days 3 hours');
<lineannotation>Result: </lineannotation><computeroutput>442800</computeroutput>
</screen>
<para>
You can convert an epoch value back to a <type>timestamp with time zone</type>
with <function>to_timestamp</function>:
</para>
<screen>
SELECT to_timestamp(982384720.12);
<lineannotation>Result: </lineannotation><computeroutput>2001-02-17 04:38:40.12+00</computeroutput>
</screen>
<para>
Beware that applying <function>to_timestamp</function> to an epoch
extracted from a <type>date</type> or <type>timestamp</type> value
could produce a misleading result: the result will effectively
assume that the original value had been given in UTC, which might
not be the case.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>hour</literal></term>
<listitem>
<para>
The hour field (0–23)
</para>
<screen>
SELECT EXTRACT(HOUR FROM TIMESTAMP '2001-02-16 20:38:40');
<lineannotation>Result: </lineannotation><computeroutput>20</computeroutput>
</screen>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>isodow</literal></term>
<listitem>
<para>
The day of the week as Monday (<literal>1</literal>) to
Sunday (<literal>7</literal>)
</para>
<screen>
SELECT EXTRACT(ISODOW FROM TIMESTAMP '2001-02-18 20:38:40');
<lineannotation>Result: </lineannotation><computeroutput>7</computeroutput>
</screen>
<para>
This is identical to <literal>dow</literal> except for Sunday. This
matches the <acronym>ISO</acronym> 8601 day of the week numbering.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>isoyear</literal></term>
<listitem>
<para>
The <acronym>ISO</acronym> 8601 week-numbering year that the date
falls in (not applicable to intervals)
</para>
<screen>
SELECT EXTRACT(ISOYEAR FROM DATE '2006-01-01');
<lineannotation>Result: </lineannotation><computeroutput>2005</computeroutput>
SELECT EXTRACT(ISOYEAR FROM DATE '2006-01-02');
<lineannotation>Result: </lineannotation><computeroutput>2006</computeroutput>
</screen>
<para>
Each <acronym>ISO</acronym> 8601 week-numbering year begins with the
Monday of the week containing the 4th of January, so in early
January or late December the <acronym>ISO</acronym> year may be
different from the Gregorian year. See the <literal>week</literal>
field for more information.
</para>
<para>
This field is not available in PostgreSQL releases prior to 8.3.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>julian</literal></term>
<listitem>
<para>
The <firstterm>Julian Date</firstterm> corresponding to the
date or timestamp (not applicable to intervals). Timestamps
that are not local midnight result in a fractional value. See
<xref linkend="datetime-julian-dates"/> for more information.
</para>
<screen>
SELECT EXTRACT(JULIAN FROM DATE '2006-01-01');
<lineannotation>Result: </lineannotation><computeroutput>2453737</computeroutput>
SELECT EXTRACT(JULIAN FROM TIMESTAMP '2006-01-01 12:00');
<lineannotation>Result: </lineannotation><computeroutput>2453737.50000000000000000000</computeroutput>
</screen>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>microseconds</literal></term>
<listitem>
<para>
The seconds field, including fractional parts, multiplied by 1
000 000; note that this includes full seconds
</para>
<screen>
SELECT EXTRACT(MICROSECONDS FROM TIME '17:12:28.5');
<lineannotation>Result: </lineannotation><computeroutput>28500000</computeroutput>
</screen>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>millennium</literal></term>
<listitem>
<para>
The millennium
</para>
<screen>
SELECT EXTRACT(MILLENNIUM FROM TIMESTAMP '2001-02-16 20:38:40');
<lineannotation>Result: </lineannotation><computeroutput>3</computeroutput>
</screen>
<para>
Years in the 1900s are in the second millennium.
The third millennium started January 1, 2001.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>milliseconds</literal></term>
<listitem>
<para>
The seconds field, including fractional parts, multiplied by
1000. Note that this includes full seconds.
</para>
<screen>
SELECT EXTRACT(MILLISECONDS FROM TIME '17:12:28.5');
<lineannotation>Result: </lineannotation><computeroutput>28500</computeroutput>
</screen>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>minute</literal></term>
<listitem>
<para>
The minutes field (0–59)
</para>
<screen>
SELECT EXTRACT(MINUTE FROM TIMESTAMP '2001-02-16 20:38:40');
<lineannotation>Result: </lineannotation><computeroutput>38</computeroutput>
</screen>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>month</literal></term>
<listitem>
<para>
For <type>timestamp</type> values, the number of the month
within the year (1–12) ; for <type>interval</type> values,
the number of months, modulo 12 (0–11)
</para>
<screen>
SELECT EXTRACT(MONTH FROM TIMESTAMP '2001-02-16 20:38:40');
<lineannotation>Result: </lineannotation><computeroutput>2</computeroutput>
SELECT EXTRACT(MONTH FROM INTERVAL '2 years 3 months');
<lineannotation>Result: </lineannotation><computeroutput>3</computeroutput>
SELECT EXTRACT(MONTH FROM INTERVAL '2 years 13 months');
<lineannotation>Result: </lineannotation><computeroutput>1</computeroutput>
</screen>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>quarter</literal></term>
<listitem>
<para>
The quarter of the year (1–4) that the date is in
</para>
<screen>
SELECT EXTRACT(QUARTER FROM TIMESTAMP '2001-02-16 20:38:40');
<lineannotation>Result: </lineannotation><computeroutput>1</computeroutput>
</screen>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>second</literal></term>
<listitem>
<para>
The seconds field, including any fractional seconds
</para>
<screen>
SELECT EXTRACT(SECOND FROM TIMESTAMP '2001-02-16 20:38:40');
<lineannotation>Result: </lineannotation><computeroutput>40</computeroutput>
SELECT EXTRACT(SECOND FROM TIME '17:12:28.5');
<lineannotation>Result: </lineannotation><computeroutput>28.5</computeroutput>
</screen>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>timezone</literal></term>
<listitem>
<para>
The time zone offset from UTC, measured in seconds. Positive values
correspond to time zones east of UTC, negative values to
zones west of UTC. (Technically,
<productname>PostgreSQL</productname> does not use UTC because
leap seconds are not handled.)
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>timezone_hour</literal></term>
<listitem>
<para>
The hour component of the time zone offset
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>timezone_minute</literal></term>
<listitem>
<para>
The minute component of the time zone offset
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>week</literal></term>
<listitem>
<para>
The number of the <acronym>ISO</acronym> 8601 week-numbering week of
the year. By definition, ISO weeks start on Mondays and the first
week of a year contains January 4 of that year. In other words, the
first Thursday of a year is in week 1 of that year.
</para>
<para>
In the ISO week-numbering system, it is possible for early-January
dates to be part of the 52nd or 53rd week of the previous year, and for
late-December dates to be part of the first week of the next year.
For example, <literal>2005-01-01</literal> is part of the 53rd week of year
2004, and <literal>2006-01-01</literal> is part of the 52nd week of year
2005, while <literal>2012-12-31</literal> is part of the first week of 2013.
It's recommended to use the <literal>isoyear</literal> field together with
<literal>week</literal> to get consistent results.
</para>
<screen>
SELECT EXTRACT(WEEK FROM TIMESTAMP '2001-02-16 20:38:40');
<lineannotation>Result: </lineannotation><computeroutput>7</computeroutput>
</screen>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>year</literal></term>
<listitem>
<para>
The year field. Keep in mind there is no <literal>0 AD</literal>, so subtracting
<literal>BC</literal> years from <literal>AD</literal> years should be done with care.
</para>
<screen>
SELECT EXTRACT(YEAR FROM TIMESTAMP '2001-02-16 20:38:40');
<lineannotation>Result: </lineannotation><computeroutput>2001</computeroutput>
</screen>
</listitem>
</varlistentry>
</variablelist>
</para>
<note>
<para>
When the input value is +/-Infinity, <function>extract</function> returns
+/-Infinity for monotonically-increasing fields (<literal>epoch</literal>,
<literal>julian</literal>, <literal>year</literal>, <literal>isoyear</literal>,
<literal>decade</literal>, <literal>century</literal>, and <literal>millennium</literal>).
For other fields, NULL is returned. <productname>PostgreSQL</productname>
versions before 9.6 returned zero for all cases of infinite input.
</para>
</note>
<para>
The <function>extract</function> function is primarily intended
for computational processing. For formatting date/time values for
display, see <xref linkend="functions-formatting"/>.
</para>
<para>
The <function>date_part</function> function is modeled on the traditional
<productname>Ingres</productname> equivalent to the
<acronym>SQL</acronym>-standard function <function>extract</function>:
<synopsis>
date_part('<replaceable>field</replaceable>', <replaceable>source</replaceable>)
</synopsis>
Note that here the <replaceable>field</replaceable> parameter needs to
be a string value, not a name. The valid field names for
<function>date_part</function> are the same as for
<function>extract</function>.
For historical reasons, the <function>date_part</function> function
returns values of type <type>double precision</type>. This can result in
a loss of precision in certain uses. Using <function>extract</function>
is recommended instead.
</para>
<screen>
SELECT date_part('day', TIMESTAMP '2001-02-16 20:38:40');
<lineannotation>Result: </lineannotation><computeroutput>16</computeroutput>
SELECT date_part('hour', INTERVAL '4 hours 3 minutes');
<lineannotation>Result: </lineannotation><computeroutput>4</computeroutput>
</screen>
</sect2>
<sect2 id="functions-datetime-trunc">
<title><function>date_trunc</function></title>
<indexterm>
<primary>date_trunc</primary>
</indexterm>
<para>
The function <function>date_trunc</function> is conceptually
similar to the <function>trunc</function> function for numbers.
</para>
<para>
<synopsis>
date_trunc(<replaceable>field</replaceable>, <replaceable>source</replaceable> [, <replaceable>time_zone</replaceable> ])
</synopsis>
<replaceable>source</replaceable> is a value expression of type
<type>timestamp</type>, <type>timestamp with time zone</type>,
or <type>interval</type>.
(Values of type <type>date</type> and
<type>time</type> are cast automatically to <type>timestamp</type> or
<type>interval</type>, respectively.)
<replaceable>field</replaceable> selects to which precision to
truncate the input value. The return value is likewise of type
<type>timestamp</type>, <type>timestamp with time zone</type>,
or <type>interval</type>,
and it has all fields that are less significant than the
selected one set to zero (or one, for day and month).
</para>
<para>
Valid values for <replaceable>field</replaceable> are:
<simplelist>
<member><literal>microseconds</literal></member>
<member><literal>milliseconds</literal></member>
<member><literal>second</literal></member>
<member><literal>minute</literal></member>
<member><literal>hour</literal></member>
<member><literal>day</literal></member>
<member><literal>week</literal></member>
<member><literal>month</literal></member>
<member><literal>quarter</literal></member>
<member><literal>year</literal></member>
<member><literal>decade</literal></member>
<member><literal>century</literal></member>
<member><literal>millennium</literal></member>
</simplelist>
</para>
<para>
When the input value is of type <type>timestamp with time zone</type>,
the truncation is performed with respect to a particular time zone;
for example, truncation to <literal>day</literal> produces a value that
is midnight in that zone. By default, truncation is done with respect
to the current <xref linkend="guc-timezone"/> setting, but the
optional <replaceable>time_zone</replaceable> argument can be provided
to specify a different time zone. The time zone name can be specified
in any of the ways described in <xref linkend="datatype-timezones"/>.
</para>
<para>
A time zone cannot be specified when processing <type>timestamp without
time zone</type> or <type>interval</type> inputs. These are always
taken at face value.
</para>
<para>
Examples (assuming the local time zone is <literal>America/New_York</literal>):
<screen>
SELECT date_trunc('hour', TIMESTAMP '2001-02-16 20:38:40');
<lineannotation>Result: </lineannotation><computeroutput>2001-02-16 20:00:00</computeroutput>
SELECT date_trunc('year', TIMESTAMP '2001-02-16 20:38:40');
<lineannotation>Result: </lineannotation><computeroutput>2001-01-01 00:00:00</computeroutput>
SELECT date_trunc('day', TIMESTAMP WITH TIME ZONE '2001-02-16 20:38:40+00');
<lineannotation>Result: </lineannotation><computeroutput>2001-02-16 00:00:00-05</computeroutput>
SELECT date_trunc('day', TIMESTAMP WITH TIME ZONE '2001-02-16 20:38:40+00', 'Australia/Sydney');
<lineannotation>Result: </lineannotation><computeroutput>2001-02-16 08:00:00-05</computeroutput>
SELECT date_trunc('hour', INTERVAL '3 days 02:47:33');
<lineannotation>Result: </lineannotation><computeroutput>3 days 02:00:00</computeroutput>
</screen>
</para>
</sect2>
<sect2 id="functions-datetime-bin">
<title><function>date_bin</function></title>
<indexterm>
<primary>date_bin</primary>
</indexterm>
<para>
The function <function>date_bin</function> <quote>bins</quote> the input
timestamp into the specified interval (the <firstterm>stride</firstterm>)
aligned with a specified origin.
</para>
<para>
<synopsis>
date_bin(<replaceable>stride</replaceable>, <replaceable>source</replaceable>, <replaceable>origin</replaceable>)
</synopsis>
<replaceable>source</replaceable> is a value expression of type
<type>timestamp</type> or <type>timestamp with time zone</type>. (Values
of type <type>date</type> are cast automatically to
<type>timestamp</type>.) <replaceable>stride</replaceable> is a value
expression of type <type>interval</type>. The return value is likewise
of type <type>timestamp</type> or <type>timestamp with time zone</type>,
and it marks the beginning of the bin into which the
<replaceable>source</replaceable> is placed.
</para>
<para>
Examples:
<screen>
SELECT date_bin('15 minutes', TIMESTAMP '2020-02-11 15:44:17', TIMESTAMP '2001-01-01');
<lineannotation>Result: </lineannotation><computeroutput>2020-02-11 15:30:00</computeroutput>
SELECT date_bin('15 minutes', TIMESTAMP '2020-02-11 15:44:17', TIMESTAMP '2001-01-01 00:02:30');
<lineannotation>Result: </lineannotation><computeroutput>2020-02-11 15:32:30</computeroutput>
</screen>
</para>
<para>
In the case of full units (1 minute, 1 hour, etc.), it gives the same result as
the analogous <function>date_trunc</function> call, but the difference is
that <function>date_bin</function> can truncate to an arbitrary interval.
</para>
<para>
The <parameter>stride</parameter> interval must be greater than zero and
cannot contain units of month or larger.
</para>
</sect2>
<sect2 id="functions-datetime-zoneconvert">
<title><literal>AT TIME ZONE</literal></title>
<indexterm>
<primary>time zone</primary>
<secondary>conversion</secondary>
</indexterm>
<indexterm>
<primary>AT TIME ZONE</primary>
</indexterm>
<para>
The <literal>AT TIME ZONE</literal> operator converts time
stamp <emphasis>without</emphasis> time zone to/from
time stamp <emphasis>with</emphasis> time zone, and
<type>time with time zone</type> values to different time
zones. <xref linkend="functions-datetime-zoneconvert-table"/> shows its
variants.
</para>
<table id="functions-datetime-zoneconvert-table">
<title><literal>AT TIME ZONE</literal> Variants</title>
<tgroup cols="1">
<thead>
<row>
<entry role="func_table_entry"><para role="func_signature">
Operator
</para>
<para>
Description
</para>
<para>
Example(s)
</para></entry>
</row>
</thead>
<tbody>
<row>
<entry role="func_table_entry"><para role="func_signature">
<type>timestamp without time zone</type> <literal>AT TIME ZONE</literal> <replaceable>zone</replaceable>
<returnvalue>timestamp with time zone</returnvalue>
</para>
<para>
Converts given time stamp <emphasis>without</emphasis> time zone to
time stamp <emphasis>with</emphasis> time zone, assuming the given
value is in the named time zone.
</para>
<para>
<literal>timestamp '2001-02-16 20:38:40' at time zone 'America/Denver'</literal>
<returnvalue>2001-02-17 03:38:40+00</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<type>timestamp with time zone</type> <literal>AT TIME ZONE</literal> <replaceable>zone</replaceable>
<returnvalue>timestamp without time zone</returnvalue>
</para>
<para>
Converts given time stamp <emphasis>with</emphasis> time zone to
time stamp <emphasis>without</emphasis> time zone, as the time would
appear in that zone.
</para>
<para>
<literal>timestamp with time zone '2001-02-16 20:38:40-05' at time zone 'America/Denver'</literal>
<returnvalue>2001-02-16 18:38:40</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<type>time with time zone</type> <literal>AT TIME ZONE</literal> <replaceable>zone</replaceable>
<returnvalue>time with time zone</returnvalue>
</para>
<para>
Converts given time <emphasis>with</emphasis> time zone to a new time
zone. Since no date is supplied, this uses the currently active UTC
offset for the named destination zone.
</para>
<para>
<literal>time with time zone '05:34:17-05' at time zone 'UTC'</literal>
<returnvalue>10:34:17+00</returnvalue>
</para></entry>
</row>
</tbody>
</tgroup>
</table>
<para>
In these expressions, the desired time zone <replaceable>zone</replaceable> can be
specified either as a text value (e.g., <literal>'America/Los_Angeles'</literal>)
or as an interval (e.g., <literal>INTERVAL '-08:00'</literal>).
In the text case, a time zone name can be specified in any of the ways
described in <xref linkend="datatype-timezones"/>.
The interval case is only useful for zones that have fixed offsets from
UTC, so it is not very common in practice.
</para>
<para>
Examples (assuming the current <xref linkend="guc-timezone"/> setting
is <literal>America/Los_Angeles</literal>):
<screen>
SELECT TIMESTAMP '2001-02-16 20:38:40' AT TIME ZONE 'America/Denver';
<lineannotation>Result: </lineannotation><computeroutput>2001-02-16 19:38:40-08</computeroutput>
SELECT TIMESTAMP WITH TIME ZONE '2001-02-16 20:38:40-05' AT TIME ZONE 'America/Denver';
<lineannotation>Result: </lineannotation><computeroutput>2001-02-16 18:38:40</computeroutput>
SELECT TIMESTAMP '2001-02-16 20:38:40' AT TIME ZONE 'Asia/Tokyo' AT TIME ZONE 'America/Chicago';
<lineannotation>Result: </lineannotation><computeroutput>2001-02-16 05:38:40</computeroutput>
</screen>
The first example adds a time zone to a value that lacks it, and
displays the value using the current <varname>TimeZone</varname>
setting. The second example shifts the time stamp with time zone value
to the specified time zone, and returns the value without a time zone.
This allows storage and display of values different from the current
<varname>TimeZone</varname> setting. The third example converts
Tokyo time to Chicago time.
</para>
<para>
The function <literal><function>timezone</function>(<replaceable>zone</replaceable>,
<replaceable>timestamp</replaceable>)</literal> is equivalent to the SQL-conforming construct
<literal><replaceable>timestamp</replaceable> AT TIME ZONE
<replaceable>zone</replaceable></literal>.
</para>
</sect2>
<sect2 id="functions-datetime-current">
<title>Current Date/Time</title>
<indexterm>
<primary>date</primary>
<secondary>current</secondary>
</indexterm>
<indexterm>
<primary>time</primary>
<secondary>current</secondary>
</indexterm>
<para>
<productname>PostgreSQL</productname> provides a number of functions
that return values related to the current date and time. These
SQL-standard functions all return values based on the start time of
the current transaction:
<synopsis>
CURRENT_DATE
CURRENT_TIME
CURRENT_TIMESTAMP
CURRENT_TIME(<replaceable>precision</replaceable>)
CURRENT_TIMESTAMP(<replaceable>precision</replaceable>)
LOCALTIME
LOCALTIMESTAMP
LOCALTIME(<replaceable>precision</replaceable>)
LOCALTIMESTAMP(<replaceable>precision</replaceable>)
</synopsis>
</para>
<para>
<function>CURRENT_TIME</function> and
<function>CURRENT_TIMESTAMP</function> deliver values with time zone;
<function>LOCALTIME</function> and
<function>LOCALTIMESTAMP</function> deliver values without time zone.
</para>
<para>
<function>CURRENT_TIME</function>,
<function>CURRENT_TIMESTAMP</function>,
<function>LOCALTIME</function>, and
<function>LOCALTIMESTAMP</function>
can optionally take
a precision parameter, which causes the result to be rounded
to that many fractional digits in the seconds field. Without a precision parameter,
the result is given to the full available precision.
</para>
<para>
Some examples:
<screen>
SELECT CURRENT_TIME;
<lineannotation>Result: </lineannotation><computeroutput>14:39:53.662522-05</computeroutput>
SELECT CURRENT_DATE;
<lineannotation>Result: </lineannotation><computeroutput>2019-12-23</computeroutput>
SELECT CURRENT_TIMESTAMP;
<lineannotation>Result: </lineannotation><computeroutput>2019-12-23 14:39:53.662522-05</computeroutput>
SELECT CURRENT_TIMESTAMP(2);
<lineannotation>Result: </lineannotation><computeroutput>2019-12-23 14:39:53.66-05</computeroutput>
SELECT LOCALTIMESTAMP;
<lineannotation>Result: </lineannotation><computeroutput>2019-12-23 14:39:53.662522</computeroutput>
</screen>
</para>
<para>
Since these functions return
the start time of the current transaction, their values do not
change during the transaction. This is considered a feature:
the intent is to allow a single transaction to have a consistent
notion of the <quote>current</quote> time, so that multiple
modifications within the same transaction bear the same
time stamp.
</para>
<note>
<para>
Other database systems might advance these values more
frequently.
</para>
</note>
<para>
<productname>PostgreSQL</productname> also provides functions that
return the start time of the current statement, as well as the actual
current time at the instant the function is called. The complete list
of non-SQL-standard time functions is:
<synopsis>
transaction_timestamp()
statement_timestamp()
clock_timestamp()
timeofday()
now()
</synopsis>
</para>
<para>
<function>transaction_timestamp()</function> is equivalent to
<function>CURRENT_TIMESTAMP</function>, but is named to clearly reflect
what it returns.
<function>statement_timestamp()</function> returns the start time of the current
statement (more specifically, the time of receipt of the latest command
message from the client).
<function>statement_timestamp()</function> and <function>transaction_timestamp()</function>
return the same value during the first command of a transaction, but might
differ during subsequent commands.
<function>clock_timestamp()</function> returns the actual current time, and
therefore its value changes even within a single SQL command.
<function>timeofday()</function> is a historical
<productname>PostgreSQL</productname> function. Like
<function>clock_timestamp()</function>, it returns the actual current time,
but as a formatted <type>text</type> string rather than a <type>timestamp
with time zone</type> value.
<function>now()</function> is a traditional <productname>PostgreSQL</productname>
equivalent to <function>transaction_timestamp()</function>.
</para>
<para>
All the date/time data types also accept the special literal value
<literal>now</literal> to specify the current date and time (again,
interpreted as the transaction start time). Thus,
the following three all return the same result:
<programlisting>
SELECT CURRENT_TIMESTAMP;
SELECT now();
SELECT TIMESTAMP 'now'; -- but see tip below
</programlisting>
</para>
<tip>
<para>
Do not use the third form when specifying a value to be evaluated later,
for example in a <literal>DEFAULT</literal> clause for a table column.
The system will convert <literal>now</literal>
to a <type>timestamp</type> as soon as the constant is parsed, so that when
the default value is needed,
the time of the table creation would be used! The first two
forms will not be evaluated until the default value is used,
because they are function calls. Thus they will give the desired
behavior of defaulting to the time of row insertion.
(See also <xref linkend="datatype-datetime-special-values"/>.)
</para>
</tip>
</sect2>
<sect2 id="functions-datetime-delay">
<title>Delaying Execution</title>
<indexterm>
<primary>pg_sleep</primary>
</indexterm>
<indexterm>
<primary>pg_sleep_for</primary>
</indexterm>
<indexterm>
<primary>pg_sleep_until</primary>
</indexterm>
<indexterm>
<primary>sleep</primary>
</indexterm>
<indexterm>
<primary>delay</primary>
</indexterm>
<para>
The following functions are available to delay execution of the server
process:
<synopsis>
pg_sleep ( <type>double precision</type> )
pg_sleep_for ( <type>interval</type> )
pg_sleep_until ( <type>timestamp with time zone</type> )
</synopsis>
<function>pg_sleep</function> makes the current session's process
sleep until the given number of seconds have
elapsed. Fractional-second delays can be specified.
<function>pg_sleep_for</function> is a convenience function to
allow the sleep time to be specified as an <type>interval</type>.
<function>pg_sleep_until</function> is a convenience function for when
a specific wake-up time is desired.
For example:
<programlisting>
SELECT pg_sleep(1.5);
SELECT pg_sleep_for('5 minutes');
SELECT pg_sleep_until('tomorrow 03:00');
</programlisting>
</para>
<note>
<para>
The effective resolution of the sleep interval is platform-specific;
0.01 seconds is a common value. The sleep delay will be at least as long
as specified. It might be longer depending on factors such as server load.
In particular, <function>pg_sleep_until</function> is not guaranteed to
wake up exactly at the specified time, but it will not wake up any earlier.
</para>
</note>
<warning>
<para>
Make sure that your session does not hold more locks than necessary
when calling <function>pg_sleep</function> or its variants. Otherwise
other sessions might have to wait for your sleeping process, slowing down
the entire system.
</para>
</warning>
</sect2>
</sect1>
<sect1 id="functions-enum">
<title>Enum Support Functions</title>
<para>
For enum types (described in <xref linkend="datatype-enum"/>),
there are several functions that allow cleaner programming without
hard-coding particular values of an enum type.
These are listed in <xref linkend="functions-enum-table"/>. The examples
assume an enum type created as:
<programlisting>
CREATE TYPE rainbow AS ENUM ('red', 'orange', 'yellow', 'green', 'blue', 'purple');
</programlisting>
</para>
<table id="functions-enum-table">
<title>Enum Support Functions</title>
<tgroup cols="1">
<thead>
<row>
<entry role="func_table_entry"><para role="func_signature">
Function
</para>
<para>
Description
</para>
<para>
Example(s)
</para></entry>
</row>
</thead>
<tbody>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>enum_first</primary>
</indexterm>
<function>enum_first</function> ( <type>anyenum</type> )
<returnvalue>anyenum</returnvalue>
</para>
<para>
Returns the first value of the input enum type.
</para>
<para>
<literal>enum_first(null::rainbow)</literal>
<returnvalue>red</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>enum_last</primary>
</indexterm>
<function>enum_last</function> ( <type>anyenum</type> )
<returnvalue>anyenum</returnvalue>
</para>
<para>
Returns the last value of the input enum type.
</para>
<para>
<literal>enum_last(null::rainbow)</literal>
<returnvalue>purple</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>enum_range</primary>
</indexterm>
<function>enum_range</function> ( <type>anyenum</type> )
<returnvalue>anyarray</returnvalue>
</para>
<para>
Returns all values of the input enum type in an ordered array.
</para>
<para>
<literal>enum_range(null::rainbow)</literal>
<returnvalue>{red,orange,yellow,&zwsp;green,blue,purple}</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<function>enum_range</function> ( <type>anyenum</type>, <type>anyenum</type> )
<returnvalue>anyarray</returnvalue>
</para>
<para>
Returns the range between the two given enum values, as an ordered
array. The values must be from the same enum type. If the first
parameter is null, the result will start with the first value of
the enum type.
If the second parameter is null, the result will end with the last
value of the enum type.
</para>
<para>
<literal>enum_range('orange'::rainbow, 'green'::rainbow)</literal>
<returnvalue>{orange,yellow,green}</returnvalue>
</para>
<para>
<literal>enum_range(NULL, 'green'::rainbow)</literal>
<returnvalue>{red,orange,&zwsp;yellow,green}</returnvalue>
</para>
<para>
<literal>enum_range('orange'::rainbow, NULL)</literal>
<returnvalue>{orange,yellow,green,&zwsp;blue,purple}</returnvalue>
</para></entry>
</row>
</tbody>
</tgroup>
</table>
<para>
Notice that except for the two-argument form of <function>enum_range</function>,
these functions disregard the specific value passed to them; they care
only about its declared data type. Either null or a specific value of
the type can be passed, with the same result. It is more common to
apply these functions to a table column or function argument than to
a hardwired type name as used in the examples.
</para>
</sect1>
<sect1 id="functions-geometry">
<title>Geometric Functions and Operators</title>
<para>
The geometric types <type>point</type>, <type>box</type>,
<type>lseg</type>, <type>line</type>, <type>path</type>,
<type>polygon</type>, and <type>circle</type> have a large set of
native support functions and operators, shown in <xref
linkend="functions-geometry-op-table"/>, <xref
linkend="functions-geometry-func-table"/>, and <xref
linkend="functions-geometry-conv-table"/>.
</para>
<table id="functions-geometry-op-table">
<title>Geometric Operators</title>
<tgroup cols="1">
<thead>
<row>
<entry role="func_table_entry"><para role="func_signature">
Operator
</para>
<para>
Description
</para>
<para>
Example(s)
</para></entry>
</row>
</thead>
<tbody>
<row>
<entry role="func_table_entry"><para role="func_signature">
<replaceable>geometric_type</replaceable> <literal>+</literal> <type>point</type>
<returnvalue><replaceable>geometric_type</replaceable></returnvalue>
</para>
<para>
Adds the coordinates of the second <type>point</type> to those of each
point of the first argument, thus performing translation.
Available for <type>point</type>, <type>box</type>, <type>path</type>,
<type>circle</type>.
</para>
<para>
<literal>box '(1,1),(0,0)' + point '(2,0)'</literal>
<returnvalue>(3,1),(2,0)</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<type>path</type> <literal>+</literal> <type>path</type>
<returnvalue>path</returnvalue>
</para>
<para>
Concatenates two open paths (returns NULL if either path is closed).
</para>
<para>
<literal>path '[(0,0),(1,1)]' + path '[(2,2),(3,3),(4,4)]'</literal>
<returnvalue>[(0,0),(1,1),(2,2),(3,3),(4,4)]</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<replaceable>geometric_type</replaceable> <literal>-</literal> <type>point</type>
<returnvalue><replaceable>geometric_type</replaceable></returnvalue>
</para>
<para>
Subtracts the coordinates of the second <type>point</type> from those
of each point of the first argument, thus performing translation.
Available for <type>point</type>, <type>box</type>, <type>path</type>,
<type>circle</type>.
</para>
<para>
<literal>box '(1,1),(0,0)' - point '(2,0)'</literal>
<returnvalue>(-1,1),(-2,0)</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<replaceable>geometric_type</replaceable> <literal>*</literal> <type>point</type>
<returnvalue><replaceable>geometric_type</replaceable></returnvalue>
</para>
<para>
Multiplies each point of the first argument by the second
<type>point</type> (treating a point as being a complex number
represented by real and imaginary parts, and performing standard
complex multiplication). If one interprets
the second <type>point</type> as a vector, this is equivalent to
scaling the object's size and distance from the origin by the length
of the vector, and rotating it counterclockwise around the origin by
the vector's angle from the <replaceable>x</replaceable> axis.
Available for <type>point</type>, <type>box</type>,<footnote
id="functions-geometry-rotation-fn"><para><quote>Rotating</quote> a
box with these operators only moves its corner points: the box is
still considered to have sides parallel to the axes. Hence the box's
size is not preserved, as a true rotation would do.</para></footnote>
<type>path</type>, <type>circle</type>.
</para>
<para>
<literal>path '((0,0),(1,0),(1,1))' * point '(3.0,0)'</literal>
<returnvalue>((0,0),(3,0),(3,3))</returnvalue>
</para>
<para>
<literal>path '((0,0),(1,0),(1,1))' * point(cosd(45), sind(45))</literal>
<returnvalue>((0,0),&zwsp;(0.7071067811865475,0.7071067811865475),&zwsp;(0,1.414213562373095))</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<replaceable>geometric_type</replaceable> <literal>/</literal> <type>point</type>
<returnvalue><replaceable>geometric_type</replaceable></returnvalue>
</para>
<para>
Divides each point of the first argument by the second
<type>point</type> (treating a point as being a complex number
represented by real and imaginary parts, and performing standard
complex division). If one interprets
the second <type>point</type> as a vector, this is equivalent to
scaling the object's size and distance from the origin down by the
length of the vector, and rotating it clockwise around the origin by
the vector's angle from the <replaceable>x</replaceable> axis.
Available for <type>point</type>, <type>box</type>,<footnoteref
linkend="functions-geometry-rotation-fn"/> <type>path</type>,
<type>circle</type>.
</para>
<para>
<literal>path '((0,0),(1,0),(1,1))' / point '(2.0,0)'</literal>
<returnvalue>((0,0),(0.5,0),(0.5,0.5))</returnvalue>
</para>
<para>
<literal>path '((0,0),(1,0),(1,1))' / point(cosd(45), sind(45))</literal>
<returnvalue>((0,0),&zwsp;(0.7071067811865476,-0.7071067811865476),&zwsp;(1.4142135623730951,0))</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<literal>@-@</literal> <replaceable>geometric_type</replaceable>
<returnvalue>double precision</returnvalue>
</para>
<para>
Computes the total length.
Available for <type>lseg</type>, <type>path</type>.
</para>
<para>
<literal>@-@ path '[(0,0),(1,0),(1,1)]'</literal>
<returnvalue>2</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<literal>@@</literal> <replaceable>geometric_type</replaceable>
<returnvalue>point</returnvalue>
</para>
<para>
Computes the center point.
Available for <type>box</type>, <type>lseg</type>, <type>path</type>,
<type>polygon</type>, <type>circle</type>.
</para>
<para>
<literal>@@ box '(2,2),(0,0)'</literal>
<returnvalue>(1,1)</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<literal>#</literal> <replaceable>geometric_type</replaceable>
<returnvalue>integer</returnvalue>
</para>
<para>
Returns the number of points.
Available for <type>path</type>, <type>polygon</type>.
</para>
<para>
<literal># path '((1,0),(0,1),(-1,0))'</literal>
<returnvalue>3</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<replaceable>geometric_type</replaceable> <literal>#</literal> <replaceable>geometric_type</replaceable>
<returnvalue>point</returnvalue>
</para>
<para>
Computes the point of intersection, or NULL if there is none.
Available for <type>lseg</type>, <type>line</type>.
</para>
<para>
<literal>lseg '[(0,0),(1,1)]' # lseg '[(1,0),(0,1)]'</literal>
<returnvalue>(0.5,0.5)</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<type>box</type> <literal>#</literal> <type>box</type>
<returnvalue>box</returnvalue>
</para>
<para>
Computes the intersection of two boxes, or NULL if there is none.
</para>
<para>
<literal>box '(2,2),(-1,-1)' # box '(1,1),(-2,-2)'</literal>
<returnvalue>(1,1),(-1,-1)</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<replaceable>geometric_type</replaceable> <literal>##</literal> <replaceable>geometric_type</replaceable>
<returnvalue>point</returnvalue>
</para>
<para>
Computes the closest point to the first object on the second object.
Available for these pairs of types:
(<type>point</type>, <type>box</type>),
(<type>point</type>, <type>lseg</type>),
(<type>point</type>, <type>line</type>),
(<type>lseg</type>, <type>box</type>),
(<type>lseg</type>, <type>lseg</type>),
(<type>lseg</type>, <type>line</type>),
(<type>line</type>, <type>box</type>),
(<type>line</type>, <type>lseg</type>).
</para>
<para>
<literal>point '(0,0)' ## lseg '[(2,0),(0,2)]'</literal>
<returnvalue>(1,1)</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<replaceable>geometric_type</replaceable> <literal><-></literal> <replaceable>geometric_type</replaceable>
<returnvalue>double precision</returnvalue>
</para>
<para>
Computes the distance between the objects.
Available for all seven geometric types, for all combinations
of <type>point</type> with another geometric type, and for
these additional pairs of types:
(<type>box</type>, <type>lseg</type>),
(<type>box</type>, <type>line</type>),
(<type>lseg</type>, <type>line</type>),
(<type>polygon</type>, <type>circle</type>)
(and the commutator cases).
</para>
<para>
<literal>circle '<(0,0),1>' <-> circle '<(5,0),1>'</literal>
<returnvalue>3</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<replaceable>geometric_type</replaceable> <literal>@></literal> <replaceable>geometric_type</replaceable>
<returnvalue>boolean</returnvalue>
</para>
<para>
Does first object contain second?
Available for these pairs of types:
(<literal>box</literal>, <literal>point</literal>),
(<literal>box</literal>, <literal>box</literal>),
(<literal>path</literal>, <literal>point</literal>),
(<literal>polygon</literal>, <literal>point</literal>),
(<literal>polygon</literal>, <literal>polygon</literal>),
(<literal>circle</literal>, <literal>point</literal>),
(<literal>circle</literal>, <literal>circle</literal>).
</para>
<para>
<literal>circle '<(0,0),2>' @> point '(1,1)'</literal>
<returnvalue>t</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<replaceable>geometric_type</replaceable> <literal><@</literal> <replaceable>geometric_type</replaceable>
<returnvalue>boolean</returnvalue>
</para>
<para>
Is first object contained in or on second?
Available for these pairs of types:
(<literal>point</literal>, <literal>box</literal>),
(<literal>point</literal>, <literal>lseg</literal>),
(<literal>point</literal>, <literal>line</literal>),
(<literal>point</literal>, <literal>path</literal>),
(<literal>point</literal>, <literal>polygon</literal>),
(<literal>point</literal>, <literal>circle</literal>),
(<literal>box</literal>, <literal>box</literal>),
(<literal>lseg</literal>, <literal>box</literal>),
(<literal>lseg</literal>, <literal>line</literal>),
(<literal>polygon</literal>, <literal>polygon</literal>),
(<literal>circle</literal>, <literal>circle</literal>).
</para>
<para>
<literal>point '(1,1)' <@ circle '<(0,0),2>'</literal>
<returnvalue>t</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<replaceable>geometric_type</replaceable> <literal>&&</literal> <replaceable>geometric_type</replaceable>
<returnvalue>boolean</returnvalue>
</para>
<para>
Do these objects overlap? (One point in common makes this true.)
Available for <type>box</type>, <type>polygon</type>,
<type>circle</type>.
</para>
<para>
<literal>box '(1,1),(0,0)' && box '(2,2),(0,0)'</literal>
<returnvalue>t</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<replaceable>geometric_type</replaceable> <literal><<</literal> <replaceable>geometric_type</replaceable>
<returnvalue>boolean</returnvalue>
</para>
<para>
Is first object strictly left of second?
Available for <type>point</type>, <type>box</type>,
<type>polygon</type>, <type>circle</type>.
</para>
<para>
<literal>circle '<(0,0),1>' << circle '<(5,0),1>'</literal>
<returnvalue>t</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<replaceable>geometric_type</replaceable> <literal>>></literal> <replaceable>geometric_type</replaceable>
<returnvalue>boolean</returnvalue>
</para>
<para>
Is first object strictly right of second?
Available for <type>point</type>, <type>box</type>,
<type>polygon</type>, <type>circle</type>.
</para>
<para>
<literal>circle '<(5,0),1>' >> circle '<(0,0),1>'</literal>
<returnvalue>t</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<replaceable>geometric_type</replaceable> <literal>&<</literal> <replaceable>geometric_type</replaceable>
<returnvalue>boolean</returnvalue>
</para>
<para>
Does first object not extend to the right of second?
Available for <type>box</type>, <type>polygon</type>,
<type>circle</type>.
</para>
<para>
<literal>box '(1,1),(0,0)' &< box '(2,2),(0,0)'</literal>
<returnvalue>t</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<replaceable>geometric_type</replaceable> <literal>&></literal> <replaceable>geometric_type</replaceable>
<returnvalue>boolean</returnvalue>
</para>
<para>
Does first object not extend to the left of second?
Available for <type>box</type>, <type>polygon</type>,
<type>circle</type>.
</para>
<para>
<literal>box '(3,3),(0,0)' &> box '(2,2),(0,0)'</literal>
<returnvalue>t</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<replaceable>geometric_type</replaceable> <literal><<|</literal> <replaceable>geometric_type</replaceable>
<returnvalue>boolean</returnvalue>
</para>
<para>
Is first object strictly below second?
Available for <type>point</type>, <type>box</type>, <type>polygon</type>,
<type>circle</type>.
</para>
<para>
<literal>box '(3,3),(0,0)' <<| box '(5,5),(3,4)'</literal>
<returnvalue>t</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<replaceable>geometric_type</replaceable> <literal>|>></literal> <replaceable>geometric_type</replaceable>
<returnvalue>boolean</returnvalue>
</para>
<para>
Is first object strictly above second?
Available for <type>point</type>, <type>box</type>, <type>polygon</type>,
<type>circle</type>.
</para>
<para>
<literal>box '(5,5),(3,4)' |>> box '(3,3),(0,0)'</literal>
<returnvalue>t</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<replaceable>geometric_type</replaceable> <literal>&<|</literal> <replaceable>geometric_type</replaceable>
<returnvalue>boolean</returnvalue>
</para>
<para>
Does first object not extend above second?
Available for <type>box</type>, <type>polygon</type>,
<type>circle</type>.
</para>
<para>
<literal>box '(1,1),(0,0)' &<| box '(2,2),(0,0)'</literal>
<returnvalue>t</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<replaceable>geometric_type</replaceable> <literal>|&></literal> <replaceable>geometric_type</replaceable>
<returnvalue>boolean</returnvalue>
</para>
<para>
Does first object not extend below second?
Available for <type>box</type>, <type>polygon</type>,
<type>circle</type>.
</para>
<para>
<literal>box '(3,3),(0,0)' |&> box '(2,2),(0,0)'</literal>
<returnvalue>t</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<type>box</type> <literal><^</literal> <type>box</type>
<returnvalue>boolean</returnvalue>
</para>
<para>
Is first object below second (allows edges to touch)?
</para>
<para>
<literal>box '((1,1),(0,0))' <^ box '((2,2),(1,1))'</literal>
<returnvalue>t</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<type>box</type> <literal>>^</literal> <type>box</type>
<returnvalue>boolean</returnvalue>
</para>
<para>
Is first object above second (allows edges to touch)?
</para>
<para>
<literal>box '((2,2),(1,1))' >^ box '((1,1),(0,0))'</literal>
<returnvalue>t</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<replaceable>geometric_type</replaceable> <literal>?#</literal> <replaceable>geometric_type</replaceable>
<returnvalue>boolean</returnvalue>
</para>
<para>
Do these objects intersect?
Available for these pairs of types:
(<type>box</type>, <type>box</type>),
(<type>lseg</type>, <type>box</type>),
(<type>lseg</type>, <type>lseg</type>),
(<type>lseg</type>, <type>line</type>),
(<type>line</type>, <type>box</type>),
(<type>line</type>, <type>line</type>),
(<type>path</type>, <type>path</type>).
</para>
<para>
<literal>lseg '[(-1,0),(1,0)]' ?# box '(2,2),(-2,-2)'</literal>
<returnvalue>t</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<literal>?-</literal> <type>line</type>
<returnvalue>boolean</returnvalue>
</para>
<para role="func_signature">
<literal>?-</literal> <type>lseg</type>
<returnvalue>boolean</returnvalue>
</para>
<para>
Is line horizontal?
</para>
<para>
<literal>?- lseg '[(-1,0),(1,0)]'</literal>
<returnvalue>t</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<type>point</type> <literal>?-</literal> <type>point</type>
<returnvalue>boolean</returnvalue>
</para>
<para>
Are points horizontally aligned (that is, have same y coordinate)?
</para>
<para>
<literal>point '(1,0)' ?- point '(0,0)'</literal>
<returnvalue>t</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<literal>?|</literal> <type>line</type>
<returnvalue>boolean</returnvalue>
</para>
<para role="func_signature">
<literal>?|</literal> <type>lseg</type>
<returnvalue>boolean</returnvalue>
</para>
<para>
Is line vertical?
</para>
<para>
<literal>?| lseg '[(-1,0),(1,0)]'</literal>
<returnvalue>f</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<type>point</type> <literal>?|</literal> <type>point</type>
<returnvalue>boolean</returnvalue>
</para>
<para>
Are points vertically aligned (that is, have same x coordinate)?
</para>
<para>
<literal>point '(0,1)' ?| point '(0,0)'</literal>
<returnvalue>t</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<type>line</type> <literal>?-|</literal> <type>line</type>
<returnvalue>boolean</returnvalue>
</para>
<para role="func_signature">
<type>lseg</type> <literal>?-|</literal> <type>lseg</type>
<returnvalue>boolean</returnvalue>
</para>
<para>
Are lines perpendicular?
</para>
<para>
<literal>lseg '[(0,0),(0,1)]' ?-| lseg '[(0,0),(1,0)]'</literal>
<returnvalue>t</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<type>line</type> <literal>?||</literal> <type>line</type>
<returnvalue>boolean</returnvalue>
</para>
<para role="func_signature">
<type>lseg</type> <literal>?||</literal> <type>lseg</type>
<returnvalue>boolean</returnvalue>
</para>
<para>
Are lines parallel?
</para>
<para>
<literal>lseg '[(-1,0),(1,0)]' ?|| lseg '[(-1,2),(1,2)]'</literal>
<returnvalue>t</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<replaceable>geometric_type</replaceable> <literal>~=</literal> <replaceable>geometric_type</replaceable>
<returnvalue>boolean</returnvalue>
</para>
<para>
Are these objects the same?
Available for <type>point</type>, <type>box</type>,
<type>polygon</type>, <type>circle</type>.
</para>
<para>
<literal>polygon '((0,0),(1,1))' ~= polygon '((1,1),(0,0))'</literal>
<returnvalue>t</returnvalue>
</para></entry>
</row>
</tbody>
</tgroup>
</table>
<caution>
<para>
Note that the <quote>same as</quote> operator, <literal>~=</literal>,
represents the usual notion of equality for the <type>point</type>,
<type>box</type>, <type>polygon</type>, and <type>circle</type> types.
Some of the geometric types also have an <literal>=</literal> operator, but
<literal>=</literal> compares for equal <emphasis>areas</emphasis> only.
The other scalar comparison operators (<literal><=</literal> and so
on), where available for these types, likewise compare areas.
</para>
</caution>
<note>
<para>
Before <productname>PostgreSQL</productname> 14, the point
is strictly below/above comparison operators <type>point</type>
<literal><<|</literal> <type>point</type> and <type>point</type>
<literal>|>></literal> <type>point</type> were respectively
called <literal><^</literal> and <literal>>^</literal>. These
names are still available, but are deprecated and will eventually be
removed.
</para>
</note>
<table id="functions-geometry-func-table">
<title>Geometric Functions</title>
<tgroup cols="1">
<thead>
<row>
<entry role="func_table_entry"><para role="func_signature">
Function
</para>
<para>
Description
</para>
<para>
Example(s)
</para></entry>
</row>
</thead>
<tbody>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>area</primary>
</indexterm>
<function>area</function> ( <replaceable>geometric_type</replaceable> )
<returnvalue>double precision</returnvalue>
</para>
<para>
Computes area.
Available for <type>box</type>, <type>path</type>, <type>circle</type>.
A <type>path</type> input must be closed, else NULL is returned.
Also, if the <type>path</type> is self-intersecting, the result may be
meaningless.
</para>
<para>
<literal>area(box '(2,2),(0,0)')</literal>
<returnvalue>4</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>center</primary>
</indexterm>
<function>center</function> ( <replaceable>geometric_type</replaceable> )
<returnvalue>point</returnvalue>
</para>
<para>
Computes center point.
Available for <type>box</type>, <type>circle</type>.
</para>
<para>
<literal>center(box '(1,2),(0,0)')</literal>
<returnvalue>(0.5,1)</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>diagonal</primary>
</indexterm>
<function>diagonal</function> ( <type>box</type> )
<returnvalue>lseg</returnvalue>
</para>
<para>
Extracts box's diagonal as a line segment
(same as <function>lseg(box)</function>).
</para>
<para>
<literal>diagonal(box '(1,2),(0,0)')</literal>
<returnvalue>[(1,2),(0,0)]</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>diameter</primary>
</indexterm>
<function>diameter</function> ( <type>circle</type> )
<returnvalue>double precision</returnvalue>
</para>
<para>
Computes diameter of circle.
</para>
<para>
<literal>diameter(circle '<(0,0),2>')</literal>
<returnvalue>4</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>height</primary>
</indexterm>
<function>height</function> ( <type>box</type> )
<returnvalue>double precision</returnvalue>
</para>
<para>
Computes vertical size of box.
</para>
<para>
<literal>height(box '(1,2),(0,0)')</literal>
<returnvalue>2</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>isclosed</primary>
</indexterm>
<function>isclosed</function> ( <type>path</type> )
<returnvalue>boolean</returnvalue>
</para>
<para>
Is path closed?
</para>
<para>
<literal>isclosed(path '((0,0),(1,1),(2,0))')</literal>
<returnvalue>t</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>isopen</primary>
</indexterm>
<function>isopen</function> ( <type>path</type> )
<returnvalue>boolean</returnvalue>
</para>
<para>
Is path open?
</para>
<para>
<literal>isopen(path '[(0,0),(1,1),(2,0)]')</literal>
<returnvalue>t</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>length</primary>
</indexterm>
<function>length</function> ( <replaceable>geometric_type</replaceable> )
<returnvalue>double precision</returnvalue>
</para>
<para>
Computes the total length.
Available for <type>lseg</type>, <type>path</type>.
</para>
<para>
<literal>length(path '((-1,0),(1,0))')</literal>
<returnvalue>4</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>npoints</primary>
</indexterm>
<function>npoints</function> ( <replaceable>geometric_type</replaceable> )
<returnvalue>integer</returnvalue>
</para>
<para>
Returns the number of points.
Available for <type>path</type>, <type>polygon</type>.
</para>
<para>
<literal>npoints(path '[(0,0),(1,1),(2,0)]')</literal>
<returnvalue>3</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pclose</primary>
</indexterm>
<function>pclose</function> ( <type>path</type> )
<returnvalue>path</returnvalue>
</para>
<para>
Converts path to closed form.
</para>
<para>
<literal>pclose(path '[(0,0),(1,1),(2,0)]')</literal>
<returnvalue>((0,0),(1,1),(2,0))</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>popen</primary>
</indexterm>
<function>popen</function> ( <type>path</type> )
<returnvalue>path</returnvalue>
</para>
<para>
Converts path to open form.
</para>
<para>
<literal>popen(path '((0,0),(1,1),(2,0))')</literal>
<returnvalue>[(0,0),(1,1),(2,0)]</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>radius</primary>
</indexterm>
<function>radius</function> ( <type>circle</type> )
<returnvalue>double precision</returnvalue>
</para>
<para>
Computes radius of circle.
</para>
<para>
<literal>radius(circle '<(0,0),2>')</literal>
<returnvalue>2</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>slope</primary>
</indexterm>
<function>slope</function> ( <type>point</type>, <type>point</type> )
<returnvalue>double precision</returnvalue>
</para>
<para>
Computes slope of a line drawn through the two points.
</para>
<para>
<literal>slope(point '(0,0)', point '(2,1)')</literal>
<returnvalue>0.5</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>width</primary>
</indexterm>
<function>width</function> ( <type>box</type> )
<returnvalue>double precision</returnvalue>
</para>
<para>
Computes horizontal size of box.
</para>
<para>
<literal>width(box '(1,2),(0,0)')</literal>
<returnvalue>1</returnvalue>
</para></entry>
</row>
</tbody>
</tgroup>
</table>
<table id="functions-geometry-conv-table">
<title>Geometric Type Conversion Functions</title>
<tgroup cols="1">
<thead>
<row>
<entry role="func_table_entry"><para role="func_signature">
Function
</para>
<para>
Description
</para>
<para>
Example(s)
</para></entry>
</row>
</thead>
<tbody>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>box</primary>
</indexterm>
<function>box</function> ( <type>circle</type> )
<returnvalue>box</returnvalue>
</para>
<para>
Computes box inscribed within the circle.
</para>
<para>
<literal>box(circle '<(0,0),2>')</literal>
<returnvalue>(1.414213562373095,1.414213562373095),&zwsp;(-1.414213562373095,-1.414213562373095)</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<function>box</function> ( <type>point</type> )
<returnvalue>box</returnvalue>
</para>
<para>
Converts point to empty box.
</para>
<para>
<literal>box(point '(1,0)')</literal>
<returnvalue>(1,0),(1,0)</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<function>box</function> ( <type>point</type>, <type>point</type> )
<returnvalue>box</returnvalue>
</para>
<para>
Converts any two corner points to box.
</para>
<para>
<literal>box(point '(0,1)', point '(1,0)')</literal>
<returnvalue>(1,1),(0,0)</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<function>box</function> ( <type>polygon</type> )
<returnvalue>box</returnvalue>
</para>
<para>
Computes bounding box of polygon.
</para>
<para>
<literal>box(polygon '((0,0),(1,1),(2,0))')</literal>
<returnvalue>(2,1),(0,0)</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>bound_box</primary>
</indexterm>
<function>bound_box</function> ( <type>box</type>, <type>box</type> )
<returnvalue>box</returnvalue>
</para>
<para>
Computes bounding box of two boxes.
</para>
<para>
<literal>bound_box(box '(1,1),(0,0)', box '(4,4),(3,3)')</literal>
<returnvalue>(4,4),(0,0)</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>circle</primary>
</indexterm>
<function>circle</function> ( <type>box</type> )
<returnvalue>circle</returnvalue>
</para>
<para>
Computes smallest circle enclosing box.
</para>
<para>
<literal>circle(box '(1,1),(0,0)')</literal>
<returnvalue><(0.5,0.5),0.7071067811865476></returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<function>circle</function> ( <type>point</type>, <type>double precision</type> )
<returnvalue>circle</returnvalue>
</para>
<para>
Constructs circle from center and radius.
</para>
<para>
<literal>circle(point '(0,0)', 2.0)</literal>
<returnvalue><(0,0),2></returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<function>circle</function> ( <type>polygon</type> )
<returnvalue>circle</returnvalue>
</para>
<para>
Converts polygon to circle. The circle's center is the mean of the
positions of the polygon's points, and the radius is the average
distance of the polygon's points from that center.
</para>
<para>
<literal>circle(polygon '((0,0),(1,3),(2,0))')</literal>
<returnvalue><(1,1),1.6094757082487299></returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>line</primary>
</indexterm>
<function>line</function> ( <type>point</type>, <type>point</type> )
<returnvalue>line</returnvalue>
</para>
<para>
Converts two points to the line through them.
</para>
<para>
<literal>line(point '(-1,0)', point '(1,0)')</literal>
<returnvalue>{0,-1,0}</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>lseg</primary>
</indexterm>
<function>lseg</function> ( <type>box</type> )
<returnvalue>lseg</returnvalue>
</para>
<para>
Extracts box's diagonal as a line segment.
</para>
<para>
<literal>lseg(box '(1,0),(-1,0)')</literal>
<returnvalue>[(1,0),(-1,0)]</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<function>lseg</function> ( <type>point</type>, <type>point</type> )
<returnvalue>lseg</returnvalue>
</para>
<para>
Constructs line segment from two endpoints.
</para>
<para>
<literal>lseg(point '(-1,0)', point '(1,0)')</literal>
<returnvalue>[(-1,0),(1,0)]</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>path</primary>
</indexterm>
<function>path</function> ( <type>polygon</type> )
<returnvalue>path</returnvalue>
</para>
<para>
Converts polygon to a closed path with the same list of points.
</para>
<para>
<literal>path(polygon '((0,0),(1,1),(2,0))')</literal>
<returnvalue>((0,0),(1,1),(2,0))</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>point</primary>
</indexterm>
<function>point</function> ( <type>double precision</type>, <type>double precision</type> )
<returnvalue>point</returnvalue>
</para>
<para>
Constructs point from its coordinates.
</para>
<para>
<literal>point(23.4, -44.5)</literal>
<returnvalue>(23.4,-44.5)</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<function>point</function> ( <type>box</type> )
<returnvalue>point</returnvalue>
</para>
<para>
Computes center of box.
</para>
<para>
<literal>point(box '(1,0),(-1,0)')</literal>
<returnvalue>(0,0)</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<function>point</function> ( <type>circle</type> )
<returnvalue>point</returnvalue>
</para>
<para>
Computes center of circle.
</para>
<para>
<literal>point(circle '<(0,0),2>')</literal>
<returnvalue>(0,0)</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<function>point</function> ( <type>lseg</type> )
<returnvalue>point</returnvalue>
</para>
<para>
Computes center of line segment.
</para>
<para>
<literal>point(lseg '[(-1,0),(1,0)]')</literal>
<returnvalue>(0,0)</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<function>point</function> ( <type>polygon</type> )
<returnvalue>point</returnvalue>
</para>
<para>
Computes center of polygon (the mean of the
positions of the polygon's points).
</para>
<para>
<literal>point(polygon '((0,0),(1,1),(2,0))')</literal>
<returnvalue>(1,0.3333333333333333)</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>polygon</primary>
</indexterm>
<function>polygon</function> ( <type>box</type> )
<returnvalue>polygon</returnvalue>
</para>
<para>
Converts box to a 4-point polygon.
</para>
<para>
<literal>polygon(box '(1,1),(0,0)')</literal>
<returnvalue>((0,0),(0,1),(1,1),(1,0))</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<function>polygon</function> ( <type>circle</type> )
<returnvalue>polygon</returnvalue>
</para>
<para>
Converts circle to a 12-point polygon.
</para>
<para>
<literal>polygon(circle '<(0,0),2>')</literal>
<returnvalue>((-2,0),&zwsp;(-1.7320508075688774,0.9999999999999999),&zwsp;(-1.0000000000000002,1.7320508075688772),&zwsp;(-1.2246063538223773e-16,2),&zwsp;(0.9999999999999996,1.7320508075688774),&zwsp;(1.732050807568877,1.0000000000000007),&zwsp;(2,2.4492127076447545e-16),&zwsp;(1.7320508075688776,-0.9999999999999994),&zwsp;(1.0000000000000009,-1.7320508075688767),&zwsp;(3.673819061467132e-16,-2),&zwsp;(-0.9999999999999987,-1.732050807568878),&zwsp;(-1.7320508075688767,-1.0000000000000009))</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<function>polygon</function> ( <type>integer</type>, <type>circle</type> )
<returnvalue>polygon</returnvalue>
</para>
<para>
Converts circle to an <replaceable>n</replaceable>-point polygon.
</para>
<para>
<literal>polygon(4, circle '<(3,0),1>')</literal>
<returnvalue>((2,0),&zwsp;(3,1),&zwsp;(4,1.2246063538223773e-16),&zwsp;(3,-1))</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<function>polygon</function> ( <type>path</type> )
<returnvalue>polygon</returnvalue>
</para>
<para>
Converts closed path to a polygon with the same list of points.
</para>
<para>
<literal>polygon(path '((0,0),(1,1),(2,0))')</literal>
<returnvalue>((0,0),(1,1),(2,0))</returnvalue>
</para></entry>
</row>
</tbody>
</tgroup>
</table>
<para>
It is possible to access the two component numbers of a <type>point</type>
as though the point were an array with indexes 0 and 1. For example, if
<literal>t.p</literal> is a <type>point</type> column then
<literal>SELECT p[0] FROM t</literal> retrieves the X coordinate and
<literal>UPDATE t SET p[1] = ...</literal> changes the Y coordinate.
In the same way, a value of type <type>box</type> or <type>lseg</type> can be treated
as an array of two <type>point</type> values.
</para>
</sect1>
<sect1 id="functions-net">
<title>Network Address Functions and Operators</title>
<para>
The IP network address types, <type>cidr</type> and <type>inet</type>,
support the usual comparison operators shown in
<xref linkend="functions-comparison-op-table"/>
as well as the specialized operators and functions shown in
<xref linkend="cidr-inet-operators-table"/> and
<xref linkend="cidr-inet-functions-table"/>.
</para>
<para>
Any <type>cidr</type> value can be cast to <type>inet</type> implicitly;
therefore, the operators and functions shown below as operating on
<type>inet</type> also work on <type>cidr</type> values. (Where there are
separate functions for <type>inet</type> and <type>cidr</type>, it is
because the behavior should be different for the two cases.)
Also, it is permitted to cast an <type>inet</type> value
to <type>cidr</type>. When this is done, any bits to the right of the
netmask are silently zeroed to create a valid <type>cidr</type> value.
</para>
<table id="cidr-inet-operators-table">
<title>IP Address Operators</title>
<tgroup cols="1">
<thead>
<row>
<entry role="func_table_entry"><para role="func_signature">
Operator
</para>
<para>
Description
</para>
<para>
Example(s)
</para></entry>
</row>
</thead>
<tbody>
<row>
<entry role="func_table_entry"><para role="func_signature">
<type>inet</type> <literal><<</literal> <type>inet</type>
<returnvalue>boolean</returnvalue>
</para>
<para>
Is subnet strictly contained by subnet?
This operator, and the next four, test for subnet inclusion. They
consider only the network parts of the two addresses (ignoring any
bits to the right of the netmasks) and determine whether one network
is identical to or a subnet of the other.
</para>
<para>
<literal>inet '192.168.1.5' << inet '192.168.1/24'</literal>
<returnvalue>t</returnvalue>
</para>
<para>
<literal>inet '192.168.0.5' << inet '192.168.1/24'</literal>
<returnvalue>f</returnvalue>
</para>
<para>
<literal>inet '192.168.1/24' << inet '192.168.1/24'</literal>
<returnvalue>f</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<type>inet</type> <literal><<=</literal> <type>inet</type>
<returnvalue>boolean</returnvalue>
</para>
<para>
Is subnet contained by or equal to subnet?
</para>
<para>
<literal>inet '192.168.1/24' <<= inet '192.168.1/24'</literal>
<returnvalue>t</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<type>inet</type> <literal>>></literal> <type>inet</type>
<returnvalue>boolean</returnvalue>
</para>
<para>
Does subnet strictly contain subnet?
</para>
<para>
<literal>inet '192.168.1/24' >> inet '192.168.1.5'</literal>
<returnvalue>t</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<type>inet</type> <literal>>>=</literal> <type>inet</type>
<returnvalue>boolean</returnvalue>
</para>
<para>
Does subnet contain or equal subnet?
</para>
<para>
<literal>inet '192.168.1/24' >>= inet '192.168.1/24'</literal>
<returnvalue>t</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<type>inet</type> <literal>&&</literal> <type>inet</type>
<returnvalue>boolean</returnvalue>
</para>
<para>
Does either subnet contain or equal the other?
</para>
<para>
<literal>inet '192.168.1/24' && inet '192.168.1.80/28'</literal>
<returnvalue>t</returnvalue>
</para>
<para>
<literal>inet '192.168.1/24' && inet '192.168.2.0/28'</literal>
<returnvalue>f</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<literal>~</literal> <type>inet</type>
<returnvalue>inet</returnvalue>
</para>
<para>
Computes bitwise NOT.
</para>
<para>
<literal>~ inet '192.168.1.6'</literal>
<returnvalue>63.87.254.249</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<type>inet</type> <literal>&</literal> <type>inet</type>
<returnvalue>inet</returnvalue>
</para>
<para>
Computes bitwise AND.
</para>
<para>
<literal>inet '192.168.1.6' & inet '0.0.0.255'</literal>
<returnvalue>0.0.0.6</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<type>inet</type> <literal>|</literal> <type>inet</type>
<returnvalue>inet</returnvalue>
</para>
<para>
Computes bitwise OR.
</para>
<para>
<literal>inet '192.168.1.6' | inet '0.0.0.255'</literal>
<returnvalue>192.168.1.255</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<type>inet</type> <literal>+</literal> <type>bigint</type>
<returnvalue>inet</returnvalue>
</para>
<para>
Adds an offset to an address.
</para>
<para>
<literal>inet '192.168.1.6' + 25</literal>
<returnvalue>192.168.1.31</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<type>bigint</type> <literal>+</literal> <type>inet</type>
<returnvalue>inet</returnvalue>
</para>
<para>
Adds an offset to an address.
</para>
<para>
<literal>200 + inet '::ffff:fff0:1'</literal>
<returnvalue>::ffff:255.240.0.201</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<type>inet</type> <literal>-</literal> <type>bigint</type>
<returnvalue>inet</returnvalue>
</para>
<para>
Subtracts an offset from an address.
</para>
<para>
<literal>inet '192.168.1.43' - 36</literal>
<returnvalue>192.168.1.7</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<type>inet</type> <literal>-</literal> <type>inet</type>
<returnvalue>bigint</returnvalue>
</para>
<para>
Computes the difference of two addresses.
</para>
<para>
<literal>inet '192.168.1.43' - inet '192.168.1.19'</literal>
<returnvalue>24</returnvalue>
</para>
<para>
<literal>inet '::1' - inet '::ffff:1'</literal>
<returnvalue>-4294901760</returnvalue>
</para></entry>
</row>
</tbody>
</tgroup>
</table>
<table id="cidr-inet-functions-table">
<title>IP Address Functions</title>
<tgroup cols="1">
<thead>
<row>
<entry role="func_table_entry"><para role="func_signature">
Function
</para>
<para>
Description
</para>
<para>
Example(s)
</para></entry>
</row>
</thead>
<tbody>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>abbrev</primary>
</indexterm>
<function>abbrev</function> ( <type>inet</type> )
<returnvalue>text</returnvalue>
</para>
<para>
Creates an abbreviated display format as text.
(The result is the same as the <type>inet</type> output function
produces; it is <quote>abbreviated</quote> only in comparison to the
result of an explicit cast to <type>text</type>, which for historical
reasons will never suppress the netmask part.)
</para>
<para>
<literal>abbrev(inet '10.1.0.0/32')</literal>
<returnvalue>10.1.0.0</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<function>abbrev</function> ( <type>cidr</type> )
<returnvalue>text</returnvalue>
</para>
<para>
Creates an abbreviated display format as text.
(The abbreviation consists of dropping all-zero octets to the right
of the netmask; more examples are in
<xref linkend="datatype-net-cidr-table"/>.)
</para>
<para>
<literal>abbrev(cidr '10.1.0.0/16')</literal>
<returnvalue>10.1/16</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>broadcast</primary>
</indexterm>
<function>broadcast</function> ( <type>inet</type> )
<returnvalue>inet</returnvalue>
</para>
<para>
Computes the broadcast address for the address's network.
</para>
<para>
<literal>broadcast(inet '192.168.1.5/24')</literal>
<returnvalue>192.168.1.255/24</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>family</primary>
</indexterm>
<function>family</function> ( <type>inet</type> )
<returnvalue>integer</returnvalue>
</para>
<para>
Returns the address's family: <literal>4</literal> for IPv4,
<literal>6</literal> for IPv6.
</para>
<para>
<literal>family(inet '::1')</literal>
<returnvalue>6</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>host</primary>
</indexterm>
<function>host</function> ( <type>inet</type> )
<returnvalue>text</returnvalue>
</para>
<para>
Returns the IP address as text, ignoring the netmask.
</para>
<para>
<literal>host(inet '192.168.1.0/24')</literal>
<returnvalue>192.168.1.0</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>hostmask</primary>
</indexterm>
<function>hostmask</function> ( <type>inet</type> )
<returnvalue>inet</returnvalue>
</para>
<para>
Computes the host mask for the address's network.
</para>
<para>
<literal>hostmask(inet '192.168.23.20/30')</literal>
<returnvalue>0.0.0.3</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>inet_merge</primary>
</indexterm>
<function>inet_merge</function> ( <type>inet</type>, <type>inet</type> )
<returnvalue>cidr</returnvalue>
</para>
<para>
Computes the smallest network that includes both of the given networks.
</para>
<para>
<literal>inet_merge(inet '192.168.1.5/24', inet '192.168.2.5/24')</literal>
<returnvalue>192.168.0.0/22</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>inet_same_family</primary>
</indexterm>
<function>inet_same_family</function> ( <type>inet</type>, <type>inet</type> )
<returnvalue>boolean</returnvalue>
</para>
<para>
Tests whether the addresses belong to the same IP family.
</para>
<para>
<literal>inet_same_family(inet '192.168.1.5/24', inet '::1')</literal>
<returnvalue>f</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>masklen</primary>
</indexterm>
<function>masklen</function> ( <type>inet</type> )
<returnvalue>integer</returnvalue>
</para>
<para>
Returns the netmask length in bits.
</para>
<para>
<literal>masklen(inet '192.168.1.5/24')</literal>
<returnvalue>24</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>netmask</primary>
</indexterm>
<function>netmask</function> ( <type>inet</type> )
<returnvalue>inet</returnvalue>
</para>
<para>
Computes the network mask for the address's network.
</para>
<para>
<literal>netmask(inet '192.168.1.5/24')</literal>
<returnvalue>255.255.255.0</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>network</primary>
</indexterm>
<function>network</function> ( <type>inet</type> )
<returnvalue>cidr</returnvalue>
</para>
<para>
Returns the network part of the address, zeroing out
whatever is to the right of the netmask.
(This is equivalent to casting the value to <type>cidr</type>.)
</para>
<para>
<literal>network(inet '192.168.1.5/24')</literal>
<returnvalue>192.168.1.0/24</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>set_masklen</primary>
</indexterm>
<function>set_masklen</function> ( <type>inet</type>, <type>integer</type> )
<returnvalue>inet</returnvalue>
</para>
<para>
Sets the netmask length for an <type>inet</type> value.
The address part does not change.
</para>
<para>
<literal>set_masklen(inet '192.168.1.5/24', 16)</literal>
<returnvalue>192.168.1.5/16</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<function>set_masklen</function> ( <type>cidr</type>, <type>integer</type> )
<returnvalue>cidr</returnvalue>
</para>
<para>
Sets the netmask length for a <type>cidr</type> value.
Address bits to the right of the new netmask are set to zero.
</para>
<para>
<literal>set_masklen(cidr '192.168.1.0/24', 16)</literal>
<returnvalue>192.168.0.0/16</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>text</primary>
</indexterm>
<function>text</function> ( <type>inet</type> )
<returnvalue>text</returnvalue>
</para>
<para>
Returns the unabbreviated IP address and netmask length as text.
(This has the same result as an explicit cast to <type>text</type>.)
</para>
<para>
<literal>text(inet '192.168.1.5')</literal>
<returnvalue>192.168.1.5/32</returnvalue>
</para></entry>
</row>
</tbody>
</tgroup>
</table>
<tip>
<para>
The <function>abbrev</function>, <function>host</function>,
and <function>text</function> functions are primarily intended to offer
alternative display formats for IP addresses.
</para>
</tip>
<para>
The MAC address types, <type>macaddr</type> and <type>macaddr8</type>,
support the usual comparison operators shown in
<xref linkend="functions-comparison-op-table"/>
as well as the specialized functions shown in
<xref linkend="macaddr-functions-table"/>.
In addition, they support the bitwise logical operators
<literal>~</literal>, <literal>&</literal> and <literal>|</literal>
(NOT, AND and OR), just as shown above for IP addresses.
</para>
<table id="macaddr-functions-table">
<title>MAC Address Functions</title>
<tgroup cols="1">
<thead>
<row>
<entry role="func_table_entry"><para role="func_signature">
Function
</para>
<para>
Description
</para>
<para>
Example(s)
</para></entry>
</row>
</thead>
<tbody>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>trunc</primary>
</indexterm>
<function>trunc</function> ( <type>macaddr</type> )
<returnvalue>macaddr</returnvalue>
</para>
<para>
Sets the last 3 bytes of the address to zero. The remaining prefix
can be associated with a particular manufacturer (using data not
included in <productname>PostgreSQL</productname>).
</para>
<para>
<literal>trunc(macaddr '12:34:56:78:90:ab')</literal>
<returnvalue>12:34:56:00:00:00</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<function>trunc</function> ( <type>macaddr8</type> )
<returnvalue>macaddr8</returnvalue>
</para>
<para>
Sets the last 5 bytes of the address to zero. The remaining prefix
can be associated with a particular manufacturer (using data not
included in <productname>PostgreSQL</productname>).
</para>
<para>
<literal>trunc(macaddr8 '12:34:56:78:90:ab:cd:ef')</literal>
<returnvalue>12:34:56:00:00:00:00:00</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>macaddr8_set7bit</primary>
</indexterm>
<function>macaddr8_set7bit</function> ( <type>macaddr8</type> )
<returnvalue>macaddr8</returnvalue>
</para>
<para>
Sets the 7th bit of the address to one, creating what is known as
modified EUI-64, for inclusion in an IPv6 address.
</para>
<para>
<literal>macaddr8_set7bit(macaddr8 '00:34:56:ab:cd:ef')</literal>
<returnvalue>02:34:56:ff:fe:ab:cd:ef</returnvalue>
</para></entry>
</row>
</tbody>
</tgroup>
</table>
</sect1>
<sect1 id="functions-textsearch">
<title>Text Search Functions and Operators</title>
<indexterm zone="datatype-textsearch">
<primary>full text search</primary>
<secondary>functions and operators</secondary>
</indexterm>
<indexterm zone="datatype-textsearch">
<primary>text search</primary>
<secondary>functions and operators</secondary>
</indexterm>
<para>
<xref linkend="textsearch-operators-table"/>,
<xref linkend="textsearch-functions-table"/> and
<xref linkend="textsearch-functions-debug-table"/>
summarize the functions and operators that are provided
for full text searching. See <xref linkend="textsearch"/> for a detailed
explanation of <productname>PostgreSQL</productname>'s text search
facility.
</para>
<table id="textsearch-operators-table">
<title>Text Search Operators</title>
<tgroup cols="1">
<thead>
<row>
<entry role="func_table_entry"><para role="func_signature">
Operator
</para>
<para>
Description
</para>
<para>
Example(s)
</para></entry>
</row>
</thead>
<tbody>
<row>
<entry role="func_table_entry"><para role="func_signature">
<type>tsvector</type> <literal>@@</literal> <type>tsquery</type>
<returnvalue>boolean</returnvalue>
</para>
<para role="func_signature">
<type>tsquery</type> <literal>@@</literal> <type>tsvector</type>
<returnvalue>boolean</returnvalue>
</para>
<para>
Does <type>tsvector</type> match <type>tsquery</type>?
(The arguments can be given in either order.)
</para>
<para>
<literal>to_tsvector('fat cats ate rats') @@ to_tsquery('cat & rat')</literal>
<returnvalue>t</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<type>text</type> <literal>@@</literal> <type>tsquery</type>
<returnvalue>boolean</returnvalue>
</para>
<para>
Does text string, after implicit invocation
of <function>to_tsvector()</function>, match <type>tsquery</type>?
</para>
<para>
<literal>'fat cats ate rats' @@ to_tsquery('cat & rat')</literal>
<returnvalue>t</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<type>tsvector</type> <literal>@@@</literal> <type>tsquery</type>
<returnvalue>boolean</returnvalue>
</para>
<para role="func_signature">
<type>tsquery</type> <literal>@@@</literal> <type>tsvector</type>
<returnvalue>boolean</returnvalue>
</para>
<para>
This is a deprecated synonym for <literal>@@</literal>.
</para>
<para>
<literal>to_tsvector('fat cats ate rats') @@@ to_tsquery('cat & rat')</literal>
<returnvalue>t</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<type>tsvector</type> <literal>||</literal> <type>tsvector</type>
<returnvalue>tsvector</returnvalue>
</para>
<para>
Concatenates two <type>tsvector</type>s. If both inputs contain
lexeme positions, the second input's positions are adjusted
accordingly.
</para>
<para>
<literal>'a:1 b:2'::tsvector || 'c:1 d:2 b:3'::tsvector</literal>
<returnvalue>'a':1 'b':2,5 'c':3 'd':4</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<type>tsquery</type> <literal>&&</literal> <type>tsquery</type>
<returnvalue>tsquery</returnvalue>
</para>
<para>
ANDs two <type>tsquery</type>s together, producing a query that
matches documents that match both input queries.
</para>
<para>
<literal>'fat | rat'::tsquery && 'cat'::tsquery</literal>
<returnvalue>( 'fat' | 'rat' ) & 'cat'</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<type>tsquery</type> <literal>||</literal> <type>tsquery</type>
<returnvalue>tsquery</returnvalue>
</para>
<para>
ORs two <type>tsquery</type>s together, producing a query that
matches documents that match either input query.
</para>
<para>
<literal>'fat | rat'::tsquery || 'cat'::tsquery</literal>
<returnvalue>'fat' | 'rat' | 'cat'</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<literal>!!</literal> <type>tsquery</type>
<returnvalue>tsquery</returnvalue>
</para>
<para>
Negates a <type>tsquery</type>, producing a query that matches
documents that do not match the input query.
</para>
<para>
<literal>!! 'cat'::tsquery</literal>
<returnvalue>!'cat'</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<type>tsquery</type> <literal><-></literal> <type>tsquery</type>
<returnvalue>tsquery</returnvalue>
</para>
<para>
Constructs a phrase query, which matches if the two input queries
match at successive lexemes.
</para>
<para>
<literal>to_tsquery('fat') <-> to_tsquery('rat')</literal>
<returnvalue>'fat' <-> 'rat'</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<type>tsquery</type> <literal>@></literal> <type>tsquery</type>
<returnvalue>boolean</returnvalue>
</para>
<para>
Does first <type>tsquery</type> contain the second? (This considers
only whether all the lexemes appearing in one query appear in the
other, ignoring the combining operators.)
</para>
<para>
<literal>'cat'::tsquery @> 'cat & rat'::tsquery</literal>
<returnvalue>f</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<type>tsquery</type> <literal><@</literal> <type>tsquery</type>
<returnvalue>boolean</returnvalue>
</para>
<para>
Is first <type>tsquery</type> contained in the second? (This
considers only whether all the lexemes appearing in one query appear
in the other, ignoring the combining operators.)
</para>
<para>
<literal>'cat'::tsquery <@ 'cat & rat'::tsquery</literal>
<returnvalue>t</returnvalue>
</para>
<para>
<literal>'cat'::tsquery <@ '!cat & rat'::tsquery</literal>
<returnvalue>t</returnvalue>
</para></entry>
</row>
</tbody>
</tgroup>
</table>
<para>
In addition to these specialized operators, the usual comparison
operators shown in <xref linkend="functions-comparison-op-table"/> are
available for types <type>tsvector</type> and <type>tsquery</type>.
These are not very
useful for text searching but allow, for example, unique indexes to be
built on columns of these types.
</para>
<table id="textsearch-functions-table">
<title>Text Search Functions</title>
<tgroup cols="1">
<thead>
<row>
<entry role="func_table_entry"><para role="func_signature">
Function
</para>
<para>
Description
</para>
<para>
Example(s)
</para></entry>
</row>
</thead>
<tbody>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>array_to_tsvector</primary>
</indexterm>
<function>array_to_tsvector</function> ( <type>text[]</type> )
<returnvalue>tsvector</returnvalue>
</para>
<para>
Converts an array of lexemes to a <type>tsvector</type>.
The given strings are used as-is without further processing.
</para>
<para>
<literal>array_to_tsvector('{fat,cat,rat}'::text[])</literal>
<returnvalue>'cat' 'fat' 'rat'</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>get_current_ts_config</primary>
</indexterm>
<function>get_current_ts_config</function> ( )
<returnvalue>regconfig</returnvalue>
</para>
<para>
Returns the OID of the current default text search configuration
(as set by <xref linkend="guc-default-text-search-config"/>).
</para>
<para>
<literal>get_current_ts_config()</literal>
<returnvalue>english</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>length</primary>
</indexterm>
<function>length</function> ( <type>tsvector</type> )
<returnvalue>integer</returnvalue>
</para>
<para>
Returns the number of lexemes in the <type>tsvector</type>.
</para>
<para>
<literal>length('fat:2,4 cat:3 rat:5A'::tsvector)</literal>
<returnvalue>3</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>numnode</primary>
</indexterm>
<function>numnode</function> ( <type>tsquery</type> )
<returnvalue>integer</returnvalue>
</para>
<para>
Returns the number of lexemes plus operators in
the <type>tsquery</type>.
</para>
<para>
<literal>numnode('(fat & rat) | cat'::tsquery)</literal>
<returnvalue>5</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>plainto_tsquery</primary>
</indexterm>
<function>plainto_tsquery</function> (
<optional> <parameter>config</parameter> <type>regconfig</type>, </optional>
<parameter>query</parameter> <type>text</type> )
<returnvalue>tsquery</returnvalue>
</para>
<para>
Converts text to a <type>tsquery</type>, normalizing words according to
the specified or default configuration. Any punctuation in the string
is ignored (it does not determine query operators). The resulting
query matches documents containing all non-stopwords in the text.
</para>
<para>
<literal>plainto_tsquery('english', 'The Fat Rats')</literal>
<returnvalue>'fat' & 'rat'</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>phraseto_tsquery</primary>
</indexterm>
<function>phraseto_tsquery</function> (
<optional> <parameter>config</parameter> <type>regconfig</type>, </optional>
<parameter>query</parameter> <type>text</type> )
<returnvalue>tsquery</returnvalue>
</para>
<para>
Converts text to a <type>tsquery</type>, normalizing words according to
the specified or default configuration. Any punctuation in the string
is ignored (it does not determine query operators). The resulting
query matches phrases containing all non-stopwords in the text.
</para>
<para>
<literal>phraseto_tsquery('english', 'The Fat Rats')</literal>
<returnvalue>'fat' <-> 'rat'</returnvalue>
</para>
<para>
<literal>phraseto_tsquery('english', 'The Cat and Rats')</literal>
<returnvalue>'cat' <2> 'rat'</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>websearch_to_tsquery</primary>
</indexterm>
<function>websearch_to_tsquery</function> (
<optional> <parameter>config</parameter> <type>regconfig</type>, </optional>
<parameter>query</parameter> <type>text</type> )
<returnvalue>tsquery</returnvalue>
</para>
<para>
Converts text to a <type>tsquery</type>, normalizing words according
to the specified or default configuration. Quoted word sequences are
converted to phrase tests. The word <quote>or</quote> is understood
as producing an OR operator, and a dash produces a NOT operator;
other punctuation is ignored.
This approximates the behavior of some common web search tools.
</para>
<para>
<literal>websearch_to_tsquery('english', '"fat rat" or cat dog')</literal>
<returnvalue>'fat' <-> 'rat' | 'cat' & 'dog'</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>querytree</primary>
</indexterm>
<function>querytree</function> ( <type>tsquery</type> )
<returnvalue>text</returnvalue>
</para>
<para>
Produces a representation of the indexable portion of
a <type>tsquery</type>. A result that is empty or
just <literal>T</literal> indicates a non-indexable query.
</para>
<para>
<literal>querytree('foo & ! bar'::tsquery)</literal>
<returnvalue>'foo'</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>setweight</primary>
</indexterm>
<function>setweight</function> ( <parameter>vector</parameter> <type>tsvector</type>, <parameter>weight</parameter> <type>"char"</type> )
<returnvalue>tsvector</returnvalue>
</para>
<para>
Assigns the specified <parameter>weight</parameter> to each element
of the <parameter>vector</parameter>.
</para>
<para>
<literal>setweight('fat:2,4 cat:3 rat:5B'::tsvector, 'A')</literal>
<returnvalue>'cat':3A 'fat':2A,4A 'rat':5A</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>setweight</primary>
<secondary>setweight for specific lexeme(s)</secondary>
</indexterm>
<function>setweight</function> ( <parameter>vector</parameter> <type>tsvector</type>, <parameter>weight</parameter> <type>"char"</type>, <parameter>lexemes</parameter> <type>text[]</type> )
<returnvalue>tsvector</returnvalue>
</para>
<para>
Assigns the specified <parameter>weight</parameter> to elements
of the <parameter>vector</parameter> that are listed
in <parameter>lexemes</parameter>.
</para>
<para>
<literal>setweight('fat:2,4 cat:3 rat:5,6B'::tsvector, 'A', '{cat,rat}')</literal>
<returnvalue>'cat':3A 'fat':2,4 'rat':5A,6A</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>strip</primary>
</indexterm>
<function>strip</function> ( <type>tsvector</type> )
<returnvalue>tsvector</returnvalue>
</para>
<para>
Removes positions and weights from the <type>tsvector</type>.
</para>
<para>
<literal>strip('fat:2,4 cat:3 rat:5A'::tsvector)</literal>
<returnvalue>'cat' 'fat' 'rat'</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>to_tsquery</primary>
</indexterm>
<function>to_tsquery</function> (
<optional> <parameter>config</parameter> <type>regconfig</type>, </optional>
<parameter>query</parameter> <type>text</type> )
<returnvalue>tsquery</returnvalue>
</para>
<para>
Converts text to a <type>tsquery</type>, normalizing words according to
the specified or default configuration. The words must be combined
by valid <type>tsquery</type> operators.
</para>
<para>
<literal>to_tsquery('english', 'The & Fat & Rats')</literal>
<returnvalue>'fat' & 'rat'</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>to_tsvector</primary>
</indexterm>
<function>to_tsvector</function> (
<optional> <parameter>config</parameter> <type>regconfig</type>, </optional>
<parameter>document</parameter> <type>text</type> )
<returnvalue>tsvector</returnvalue>
</para>
<para>
Converts text to a <type>tsvector</type>, normalizing words according
to the specified or default configuration. Position information is
included in the result.
</para>
<para>
<literal>to_tsvector('english', 'The Fat Rats')</literal>
<returnvalue>'fat':2 'rat':3</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<function>to_tsvector</function> (
<optional> <parameter>config</parameter> <type>regconfig</type>, </optional>
<parameter>document</parameter> <type>json</type> )
<returnvalue>tsvector</returnvalue>
</para>
<para role="func_signature">
<function>to_tsvector</function> (
<optional> <parameter>config</parameter> <type>regconfig</type>, </optional>
<parameter>document</parameter> <type>jsonb</type> )
<returnvalue>tsvector</returnvalue>
</para>
<para>
Converts each string value in the JSON document to
a <type>tsvector</type>, normalizing words according to the specified
or default configuration. The results are then concatenated in
document order to produce the output. Position information is
generated as though one stopword exists between each pair of string
values. (Beware that <quote>document order</quote> of the fields of a
JSON object is implementation-dependent when the input
is <type>jsonb</type>; observe the difference in the examples.)
</para>
<para>
<literal>to_tsvector('english', '{"aa": "The Fat Rats", "b": "dog"}'::json)</literal>
<returnvalue>'dog':5 'fat':2 'rat':3</returnvalue>
</para>
<para>
<literal>to_tsvector('english', '{"aa": "The Fat Rats", "b": "dog"}'::jsonb)</literal>
<returnvalue>'dog':1 'fat':4 'rat':5</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>json_to_tsvector</primary>
</indexterm>
<function>json_to_tsvector</function> (
<optional> <parameter>config</parameter> <type>regconfig</type>, </optional>
<parameter>document</parameter> <type>json</type>,
<parameter>filter</parameter> <type>jsonb</type> )
<returnvalue>tsvector</returnvalue>
</para>
<para role="func_signature">
<indexterm>
<primary>jsonb_to_tsvector</primary>
</indexterm>
<function>jsonb_to_tsvector</function> (
<optional> <parameter>config</parameter> <type>regconfig</type>, </optional>
<parameter>document</parameter> <type>jsonb</type>,
<parameter>filter</parameter> <type>jsonb</type> )
<returnvalue>tsvector</returnvalue>
</para>
<para>
Selects each item in the JSON document that is requested by
the <parameter>filter</parameter> and converts each one to
a <type>tsvector</type>, normalizing words according to the specified
or default configuration. The results are then concatenated in
document order to produce the output. Position information is
generated as though one stopword exists between each pair of selected
items. (Beware that <quote>document order</quote> of the fields of a
JSON object is implementation-dependent when the input
is <type>jsonb</type>.)
The <parameter>filter</parameter> must be a <type>jsonb</type>
array containing zero or more of these keywords:
<literal>"string"</literal> (to include all string values),
<literal>"numeric"</literal> (to include all numeric values),
<literal>"boolean"</literal> (to include all boolean values),
<literal>"key"</literal> (to include all keys), or
<literal>"all"</literal> (to include all the above).
As a special case, the <parameter>filter</parameter> can also be a
simple JSON value that is one of these keywords.
</para>
<para>
<literal>json_to_tsvector('english', '{"a": "The Fat Rats", "b": 123}'::json, '["string", "numeric"]')</literal>
<returnvalue>'123':5 'fat':2 'rat':3</returnvalue>
</para>
<para>
<literal>json_to_tsvector('english', '{"cat": "The Fat Rats", "dog": 123}'::json, '"all"')</literal>
<returnvalue>'123':9 'cat':1 'dog':7 'fat':4 'rat':5</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>ts_delete</primary>
</indexterm>
<function>ts_delete</function> ( <parameter>vector</parameter> <type>tsvector</type>, <parameter>lexeme</parameter> <type>text</type> )
<returnvalue>tsvector</returnvalue>
</para>
<para>
Removes any occurrence of the given <parameter>lexeme</parameter>
from the <parameter>vector</parameter>.
</para>
<para>
<literal>ts_delete('fat:2,4 cat:3 rat:5A'::tsvector, 'fat')</literal>
<returnvalue>'cat':3 'rat':5A</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<function>ts_delete</function> ( <parameter>vector</parameter> <type>tsvector</type>, <parameter>lexemes</parameter> <type>text[]</type> )
<returnvalue>tsvector</returnvalue>
</para>
<para>
Removes any occurrences of the lexemes
in <parameter>lexemes</parameter>
from the <parameter>vector</parameter>.
</para>
<para>
<literal>ts_delete('fat:2,4 cat:3 rat:5A'::tsvector, ARRAY['fat','rat'])</literal>
<returnvalue>'cat':3</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>ts_filter</primary>
</indexterm>
<function>ts_filter</function> ( <parameter>vector</parameter> <type>tsvector</type>, <parameter>weights</parameter> <type>"char"[]</type> )
<returnvalue>tsvector</returnvalue>
</para>
<para>
Selects only elements with the given <parameter>weights</parameter>
from the <parameter>vector</parameter>.
</para>
<para>
<literal>ts_filter('fat:2,4 cat:3b,7c rat:5A'::tsvector, '{a,b}')</literal>
<returnvalue>'cat':3B 'rat':5A</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>ts_headline</primary>
</indexterm>
<function>ts_headline</function> (
<optional> <parameter>config</parameter> <type>regconfig</type>, </optional>
<parameter>document</parameter> <type>text</type>,
<parameter>query</parameter> <type>tsquery</type>
<optional>, <parameter>options</parameter> <type>text</type> </optional> )
<returnvalue>text</returnvalue>
</para>
<para>
Displays, in an abbreviated form, the match(es) for
the <parameter>query</parameter> in
the <parameter>document</parameter>, which must be raw text not
a <type>tsvector</type>. Words in the document are normalized
according to the specified or default configuration before matching to
the query. Use of this function is discussed in
<xref linkend="textsearch-headline"/>, which also describes the
available <parameter>options</parameter>.
</para>
<para>
<literal>ts_headline('The fat cat ate the rat.', 'cat')</literal>
<returnvalue>The fat <b>cat</b> ate the rat.</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<function>ts_headline</function> (
<optional> <parameter>config</parameter> <type>regconfig</type>, </optional>
<parameter>document</parameter> <type>json</type>,
<parameter>query</parameter> <type>tsquery</type>
<optional>, <parameter>options</parameter> <type>text</type> </optional> )
<returnvalue>text</returnvalue>
</para>
<para role="func_signature">
<function>ts_headline</function> (
<optional> <parameter>config</parameter> <type>regconfig</type>, </optional>
<parameter>document</parameter> <type>jsonb</type>,
<parameter>query</parameter> <type>tsquery</type>
<optional>, <parameter>options</parameter> <type>text</type> </optional> )
<returnvalue>text</returnvalue>
</para>
<para>
Displays, in an abbreviated form, match(es) for
the <parameter>query</parameter> that occur in string values
within the JSON <parameter>document</parameter>.
See <xref linkend="textsearch-headline"/> for more details.
</para>
<para>
<literal>ts_headline('{"cat":"raining cats and dogs"}'::jsonb, 'cat')</literal>
<returnvalue>{"cat": "raining <b>cats</b> and dogs"}</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>ts_rank</primary>
</indexterm>
<function>ts_rank</function> (
<optional> <parameter>weights</parameter> <type>real[]</type>, </optional>
<parameter>vector</parameter> <type>tsvector</type>,
<parameter>query</parameter> <type>tsquery</type>
<optional>, <parameter>normalization</parameter> <type>integer</type> </optional> )
<returnvalue>real</returnvalue>
</para>
<para>
Computes a score showing how well
the <parameter>vector</parameter> matches
the <parameter>query</parameter>. See
<xref linkend="textsearch-ranking"/> for details.
</para>
<para>
<literal>ts_rank(to_tsvector('raining cats and dogs'), 'cat')</literal>
<returnvalue>0.06079271</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>ts_rank_cd</primary>
</indexterm>
<function>ts_rank_cd</function> (
<optional> <parameter>weights</parameter> <type>real[]</type>, </optional>
<parameter>vector</parameter> <type>tsvector</type>,
<parameter>query</parameter> <type>tsquery</type>
<optional>, <parameter>normalization</parameter> <type>integer</type> </optional> )
<returnvalue>real</returnvalue>
</para>
<para>
Computes a score showing how well
the <parameter>vector</parameter> matches
the <parameter>query</parameter>, using a cover density
algorithm. See <xref linkend="textsearch-ranking"/> for details.
</para>
<para>
<literal>ts_rank_cd(to_tsvector('raining cats and dogs'), 'cat')</literal>
<returnvalue>0.1</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>ts_rewrite</primary>
</indexterm>
<function>ts_rewrite</function> ( <parameter>query</parameter> <type>tsquery</type>,
<parameter>target</parameter> <type>tsquery</type>,
<parameter>substitute</parameter> <type>tsquery</type> )
<returnvalue>tsquery</returnvalue>
</para>
<para>
Replaces occurrences of <parameter>target</parameter>
with <parameter>substitute</parameter>
within the <parameter>query</parameter>.
See <xref linkend="textsearch-query-rewriting"/> for details.
</para>
<para>
<literal>ts_rewrite('a & b'::tsquery, 'a'::tsquery, 'foo|bar'::tsquery)</literal>
<returnvalue>'b' & ( 'foo' | 'bar' )</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<function>ts_rewrite</function> ( <parameter>query</parameter> <type>tsquery</type>,
<parameter>select</parameter> <type>text</type> )
<returnvalue>tsquery</returnvalue>
</para>
<para>
Replaces portions of the <parameter>query</parameter> according to
target(s) and substitute(s) obtained by executing
a <command>SELECT</command> command.
See <xref linkend="textsearch-query-rewriting"/> for details.
</para>
<para>
<literal>SELECT ts_rewrite('a & b'::tsquery, 'SELECT t,s FROM aliases')</literal>
<returnvalue>'b' & ( 'foo' | 'bar' )</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>tsquery_phrase</primary>
</indexterm>
<function>tsquery_phrase</function> ( <parameter>query1</parameter> <type>tsquery</type>, <parameter>query2</parameter> <type>tsquery</type> )
<returnvalue>tsquery</returnvalue>
</para>
<para>
Constructs a phrase query that searches
for matches of <parameter>query1</parameter>
and <parameter>query2</parameter> at successive lexemes (same
as <literal><-></literal> operator).
</para>
<para>
<literal>tsquery_phrase(to_tsquery('fat'), to_tsquery('cat'))</literal>
<returnvalue>'fat' <-> 'cat'</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<function>tsquery_phrase</function> ( <parameter>query1</parameter> <type>tsquery</type>, <parameter>query2</parameter> <type>tsquery</type>, <parameter>distance</parameter> <type>integer</type> )
<returnvalue>tsquery</returnvalue>
</para>
<para>
Constructs a phrase query that searches
for matches of <parameter>query1</parameter> and
<parameter>query2</parameter> that occur exactly
<parameter>distance</parameter> lexemes apart.
</para>
<para>
<literal>tsquery_phrase(to_tsquery('fat'), to_tsquery('cat'), 10)</literal>
<returnvalue>'fat' <10> 'cat'</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>tsvector_to_array</primary>
</indexterm>
<function>tsvector_to_array</function> ( <type>tsvector</type> )
<returnvalue>text[]</returnvalue>
</para>
<para>
Converts a <type>tsvector</type> to an array of lexemes.
</para>
<para>
<literal>tsvector_to_array('fat:2,4 cat:3 rat:5A'::tsvector)</literal>
<returnvalue>{cat,fat,rat}</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>unnest</primary>
<secondary>for tsvector</secondary>
</indexterm>
<function>unnest</function> ( <type>tsvector</type> )
<returnvalue>setof record</returnvalue>
( <parameter>lexeme</parameter> <type>text</type>,
<parameter>positions</parameter> <type>smallint[]</type>,
<parameter>weights</parameter> <type>text</type> )
</para>
<para>
Expands a <type>tsvector</type> into a set of rows, one per lexeme.
</para>
<para>
<literal>select * from unnest('cat:3 fat:2,4 rat:5A'::tsvector)</literal>
<returnvalue></returnvalue>
<programlisting>
lexeme | positions | weights
--------+-----------+---------
cat | {3} | {D}
fat | {2,4} | {D,D}
rat | {5} | {A}
</programlisting>
</para></entry>
</row>
</tbody>
</tgroup>
</table>
<note>
<para>
All the text search functions that accept an optional <type>regconfig</type>
argument will use the configuration specified by
<xref linkend="guc-default-text-search-config"/>
when that argument is omitted.
</para>
</note>
<para>
The functions in
<xref linkend="textsearch-functions-debug-table"/>
are listed separately because they are not usually used in everyday text
searching operations. They are primarily helpful for development and
debugging of new text search configurations.
</para>
<table id="textsearch-functions-debug-table">
<title>Text Search Debugging Functions</title>
<tgroup cols="1">
<thead>
<row>
<entry role="func_table_entry"><para role="func_signature">
Function
</para>
<para>
Description
</para>
<para>
Example(s)
</para></entry>
</row>
</thead>
<tbody>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>ts_debug</primary>
</indexterm>
<function>ts_debug</function> (
<optional> <parameter>config</parameter> <type>regconfig</type>, </optional>
<parameter>document</parameter> <type>text</type> )
<returnvalue>setof record</returnvalue>
( <parameter>alias</parameter> <type>text</type>,
<parameter>description</parameter> <type>text</type>,
<parameter>token</parameter> <type>text</type>,
<parameter>dictionaries</parameter> <type>regdictionary[]</type>,
<parameter>dictionary</parameter> <type>regdictionary</type>,
<parameter>lexemes</parameter> <type>text[]</type> )
</para>
<para>
Extracts and normalizes tokens from
the <parameter>document</parameter> according to the specified or
default text search configuration, and returns information about how
each token was processed.
See <xref linkend="textsearch-configuration-testing"/> for details.
</para>
<para>
<literal>ts_debug('english', 'The Brightest supernovaes')</literal>
<returnvalue>(asciiword,"Word, all ASCII",The,{english_stem},english_stem,{}) ...</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>ts_lexize</primary>
</indexterm>
<function>ts_lexize</function> ( <parameter>dict</parameter> <type>regdictionary</type>, <parameter>token</parameter> <type>text</type> )
<returnvalue>text[]</returnvalue>
</para>
<para>
Returns an array of replacement lexemes if the input token is known to
the dictionary, or an empty array if the token is known to the
dictionary but it is a stop word, or NULL if it is not a known word.
See <xref linkend="textsearch-dictionary-testing"/> for details.
</para>
<para>
<literal>ts_lexize('english_stem', 'stars')</literal>
<returnvalue>{star}</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>ts_parse</primary>
</indexterm>
<function>ts_parse</function> ( <parameter>parser_name</parameter> <type>text</type>,
<parameter>document</parameter> <type>text</type> )
<returnvalue>setof record</returnvalue>
( <parameter>tokid</parameter> <type>integer</type>,
<parameter>token</parameter> <type>text</type> )
</para>
<para>
Extracts tokens from the <parameter>document</parameter> using the
named parser.
See <xref linkend="textsearch-parser-testing"/> for details.
</para>
<para>
<literal>ts_parse('default', 'foo - bar')</literal>
<returnvalue>(1,foo) ...</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<function>ts_parse</function> ( <parameter>parser_oid</parameter> <type>oid</type>,
<parameter>document</parameter> <type>text</type> )
<returnvalue>setof record</returnvalue>
( <parameter>tokid</parameter> <type>integer</type>,
<parameter>token</parameter> <type>text</type> )
</para>
<para>
Extracts tokens from the <parameter>document</parameter> using a
parser specified by OID.
See <xref linkend="textsearch-parser-testing"/> for details.
</para>
<para>
<literal>ts_parse(3722, 'foo - bar')</literal>
<returnvalue>(1,foo) ...</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>ts_token_type</primary>
</indexterm>
<function>ts_token_type</function> ( <parameter>parser_name</parameter> <type>text</type> )
<returnvalue>setof record</returnvalue>
( <parameter>tokid</parameter> <type>integer</type>,
<parameter>alias</parameter> <type>text</type>,
<parameter>description</parameter> <type>text</type> )
</para>
<para>
Returns a table that describes each type of token the named parser can
recognize.
See <xref linkend="textsearch-parser-testing"/> for details.
</para>
<para>
<literal>ts_token_type('default')</literal>
<returnvalue>(1,asciiword,"Word, all ASCII") ...</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<function>ts_token_type</function> ( <parameter>parser_oid</parameter> <type>oid</type> )
<returnvalue>setof record</returnvalue>
( <parameter>tokid</parameter> <type>integer</type>,
<parameter>alias</parameter> <type>text</type>,
<parameter>description</parameter> <type>text</type> )
</para>
<para>
Returns a table that describes each type of token a parser specified
by OID can recognize.
See <xref linkend="textsearch-parser-testing"/> for details.
</para>
<para>
<literal>ts_token_type(3722)</literal>
<returnvalue>(1,asciiword,"Word, all ASCII") ...</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>ts_stat</primary>
</indexterm>
<function>ts_stat</function> ( <parameter>sqlquery</parameter> <type>text</type>
<optional>, <parameter>weights</parameter> <type>text</type> </optional> )
<returnvalue>setof record</returnvalue>
( <parameter>word</parameter> <type>text</type>,
<parameter>ndoc</parameter> <type>integer</type>,
<parameter>nentry</parameter> <type>integer</type> )
</para>
<para>
Executes the <parameter>sqlquery</parameter>, which must return a
single <type>tsvector</type> column, and returns statistics about each
distinct lexeme contained in the data.
See <xref linkend="textsearch-statistics"/> for details.
</para>
<para>
<literal>ts_stat('SELECT vector FROM apod')</literal>
<returnvalue>(foo,10,15) ...</returnvalue>
</para></entry>
</row>
</tbody>
</tgroup>
</table>
</sect1>
<sect1 id="functions-uuid">
<title>UUID Functions</title>
<indexterm zone="datatype-uuid">
<primary>UUID</primary>
<secondary>generating</secondary>
</indexterm>
<indexterm>
<primary>gen_random_uuid</primary>
</indexterm>
<para>
<productname>PostgreSQL</productname> includes one function to generate a UUID:
<synopsis>
<function>gen_random_uuid</function> () <returnvalue>uuid</returnvalue>
</synopsis>
This function returns a version 4 (random) UUID. This is the most commonly
used type of UUID and is appropriate for most applications.
</para>
<para>
The <xref linkend="uuid-ossp"/> module provides additional functions that
implement other standard algorithms for generating UUIDs.
</para>
<para>
<productname>PostgreSQL</productname> also provides the usual comparison
operators shown in <xref linkend="functions-comparison-op-table"/> for
UUIDs.
</para>
</sect1>
<sect1 id="functions-xml">
<title>XML Functions</title>
<indexterm>
<primary>XML Functions</primary>
</indexterm>
<para>
The functions and function-like expressions described in this
section operate on values of type <type>xml</type>. See <xref
linkend="datatype-xml"/> for information about the <type>xml</type>
type. The function-like expressions <function>xmlparse</function>
and <function>xmlserialize</function> for converting to and from
type <type>xml</type> are documented there, not in this section.
</para>
<para>
Use of most of these functions
requires <productname>PostgreSQL</productname> to have been built
with <command>configure --with-libxml</command>.
</para>
<sect2 id="functions-producing-xml">
<title>Producing XML Content</title>
<para>
A set of functions and function-like expressions is available for
producing XML content from SQL data. As such, they are
particularly suitable for formatting query results into XML
documents for processing in client applications.
</para>
<sect3>
<title><literal>xmlcomment</literal></title>
<indexterm>
<primary>xmlcomment</primary>
</indexterm>
<synopsis>
<function>xmlcomment</function> ( <type>text</type> ) <returnvalue>xml</returnvalue>
</synopsis>
<para>
The function <function>xmlcomment</function> creates an XML value
containing an XML comment with the specified text as content.
The text cannot contain <quote><literal>--</literal></quote> or end with a
<quote><literal>-</literal></quote>, otherwise the resulting construct
would not be a valid XML comment.
If the argument is null, the result is null.
</para>
<para>
Example:
<screen><![CDATA[
SELECT xmlcomment('hello');
xmlcomment
--------------
<!--hello-->
]]></screen>
</para>
</sect3>
<sect3>
<title><literal>xmlconcat</literal></title>
<indexterm>
<primary>xmlconcat</primary>
</indexterm>
<synopsis>
<function>xmlconcat</function> ( <type>xml</type> <optional>, ...</optional> ) <returnvalue>xml</returnvalue>
</synopsis>
<para>
The function <function>xmlconcat</function> concatenates a list
of individual XML values to create a single value containing an
XML content fragment. Null values are omitted; the result is
only null if there are no nonnull arguments.
</para>
<para>
Example:
<screen><![CDATA[
SELECT xmlconcat('<abc/>', '<bar>foo</bar>');
xmlconcat
----------------------
<abc/><bar>foo</bar>
]]></screen>
</para>
<para>
XML declarations, if present, are combined as follows. If all
argument values have the same XML version declaration, that
version is used in the result, else no version is used. If all
argument values have the standalone declaration value
<quote>yes</quote>, then that value is used in the result. If
all argument values have a standalone declaration value and at
least one is <quote>no</quote>, then that is used in the result.
Else the result will have no standalone declaration. If the
result is determined to require a standalone declaration but no
version declaration, a version declaration with version 1.0 will
be used because XML requires an XML declaration to contain a
version declaration. Encoding declarations are ignored and
removed in all cases.
</para>
<para>
Example:
<screen><![CDATA[
SELECT xmlconcat('<?xml version="1.1"?><foo/>', '<?xml version="1.1" standalone="no"?><bar/>');
xmlconcat
-----------------------------------
<?xml version="1.1"?><foo/><bar/>
]]></screen>
</para>
</sect3>
<sect3>
<title><literal>xmlelement</literal></title>
<indexterm>
<primary>xmlelement</primary>
</indexterm>
<synopsis>
<function>xmlelement</function> ( <literal>NAME</literal> <replaceable>name</replaceable> <optional>, <literal>XMLATTRIBUTES</literal> ( <replaceable>attvalue</replaceable> <optional> <literal>AS</literal> <replaceable>attname</replaceable> </optional> <optional>, ...</optional> ) </optional> <optional>, <replaceable>content</replaceable> <optional>, ...</optional></optional> ) <returnvalue>xml</returnvalue>
</synopsis>
<para>
The <function>xmlelement</function> expression produces an XML
element with the given name, attributes, and content.
The <replaceable>name</replaceable>
and <replaceable>attname</replaceable> items shown in the syntax are
simple identifiers, not values. The <replaceable>attvalue</replaceable>
and <replaceable>content</replaceable> items are expressions, which can
yield any <productname>PostgreSQL</productname> data type. The
argument(s) within <literal>XMLATTRIBUTES</literal> generate attributes
of the XML element; the <replaceable>content</replaceable> value(s) are
concatenated to form its content.
</para>
<para>
Examples:
<screen><![CDATA[
SELECT xmlelement(name foo);
xmlelement
------------
<foo/>
SELECT xmlelement(name foo, xmlattributes('xyz' as bar));
xmlelement
------------------
<foo bar="xyz"/>
SELECT xmlelement(name foo, xmlattributes(current_date as bar), 'cont', 'ent');
xmlelement
-------------------------------------
<foo bar="2007-01-26">content</foo>
]]></screen>
</para>
<para>
Element and attribute names that are not valid XML names are
escaped by replacing the offending characters by the sequence
<literal>_x<replaceable>HHHH</replaceable>_</literal>, where
<replaceable>HHHH</replaceable> is the character's Unicode
codepoint in hexadecimal notation. For example:
<screen><![CDATA[
SELECT xmlelement(name "foo$bar", xmlattributes('xyz' as "a&b"));
xmlelement
----------------------------------
<foo_x0024_bar a_x0026_b="xyz"/>
]]></screen>
</para>
<para>
An explicit attribute name need not be specified if the attribute
value is a column reference, in which case the column's name will
be used as the attribute name by default. In other cases, the
attribute must be given an explicit name. So this example is
valid:
<screen>
CREATE TABLE test (a xml, b xml);
SELECT xmlelement(name test, xmlattributes(a, b)) FROM test;
</screen>
But these are not:
<screen>
SELECT xmlelement(name test, xmlattributes('constant'), a, b) FROM test;
SELECT xmlelement(name test, xmlattributes(func(a, b))) FROM test;
</screen>
</para>
<para>
Element content, if specified, will be formatted according to
its data type. If the content is itself of type <type>xml</type>,
complex XML documents can be constructed. For example:
<screen><![CDATA[
SELECT xmlelement(name foo, xmlattributes('xyz' as bar),
xmlelement(name abc),
xmlcomment('test'),
xmlelement(name xyz));
xmlelement
----------------------------------------------
<foo bar="xyz"><abc/><!--test--><xyz/></foo>
]]></screen>
Content of other types will be formatted into valid XML character
data. This means in particular that the characters <, >,
and & will be converted to entities. Binary data (data type
<type>bytea</type>) will be represented in base64 or hex
encoding, depending on the setting of the configuration parameter
<xref linkend="guc-xmlbinary"/>. The particular behavior for
individual data types is expected to evolve in order to align the
PostgreSQL mappings with those specified in SQL:2006 and later,
as discussed in <xref linkend="functions-xml-limits-casts"/>.
</para>
</sect3>
<sect3>
<title><literal>xmlforest</literal></title>
<indexterm>
<primary>xmlforest</primary>
</indexterm>
<synopsis>
<function>xmlforest</function> ( <replaceable>content</replaceable> <optional> <literal>AS</literal> <replaceable>name</replaceable> </optional> <optional>, ...</optional> ) <returnvalue>xml</returnvalue>
</synopsis>
<para>
The <function>xmlforest</function> expression produces an XML
forest (sequence) of elements using the given names and content.
As for <function>xmlelement</function>,
each <replaceable>name</replaceable> must be a simple identifier, while
the <replaceable>content</replaceable> expressions can have any data
type.
</para>
<para>
Examples:
<screen>
SELECT xmlforest('abc' AS foo, 123 AS bar);
xmlforest
------------------------------
<foo>abc</foo><bar>123</bar>
SELECT xmlforest(table_name, column_name)
FROM information_schema.columns
WHERE table_schema = 'pg_catalog';
xmlforest
------------------------------------&zwsp;-----------------------------------
<table_name>pg_authid</table_name>&zwsp;<column_name>rolname</column_name>
<table_name>pg_authid</table_name>&zwsp;<column_name>rolsuper</column_name>
...
</screen>
As seen in the second example, the element name can be omitted if
the content value is a column reference, in which case the column
name is used by default. Otherwise, a name must be specified.
</para>
<para>
Element names that are not valid XML names are escaped as shown
for <function>xmlelement</function> above. Similarly, content
data is escaped to make valid XML content, unless it is already
of type <type>xml</type>.
</para>
<para>
Note that XML forests are not valid XML documents if they consist
of more than one element, so it might be useful to wrap
<function>xmlforest</function> expressions in
<function>xmlelement</function>.
</para>
</sect3>
<sect3>
<title><literal>xmlpi</literal></title>
<indexterm>
<primary>xmlpi</primary>
</indexterm>
<synopsis>
<function>xmlpi</function> ( <literal>NAME</literal> <replaceable>name</replaceable> <optional>, <replaceable>content</replaceable> </optional> ) <returnvalue>xml</returnvalue>
</synopsis>
<para>
The <function>xmlpi</function> expression creates an XML
processing instruction.
As for <function>xmlelement</function>,
the <replaceable>name</replaceable> must be a simple identifier, while
the <replaceable>content</replaceable> expression can have any data type.
The <replaceable>content</replaceable>, if present, must not contain the
character sequence <literal>?></literal>.
</para>
<para>
Example:
<screen><![CDATA[
SELECT xmlpi(name php, 'echo "hello world";');
xmlpi
-----------------------------
<?php echo "hello world";?>
]]></screen>
</para>
</sect3>
<sect3>
<title><literal>xmlroot</literal></title>
<indexterm>
<primary>xmlroot</primary>
</indexterm>
<synopsis>
<function>xmlroot</function> ( <type>xml</type>, <literal>VERSION</literal> {<type>text</type>|<literal>NO VALUE</literal>} <optional>, <literal>STANDALONE</literal> {<literal>YES</literal>|<literal>NO</literal>|<literal>NO VALUE</literal>} </optional> ) <returnvalue>xml</returnvalue>
</synopsis>
<para>
The <function>xmlroot</function> expression alters the properties
of the root node of an XML value. If a version is specified,
it replaces the value in the root node's version declaration; if a
standalone setting is specified, it replaces the value in the
root node's standalone declaration.
</para>
<para>
<screen><![CDATA[
SELECT xmlroot(xmlparse(document '<?xml version="1.1"?><content>abc</content>'),
version '1.0', standalone yes);
xmlroot
----------------------------------------
<?xml version="1.0" standalone="yes"?>
<content>abc</content>
]]></screen>
</para>
</sect3>
<sect3 id="functions-xml-xmlagg">
<title><literal>xmlagg</literal></title>
<indexterm>
<primary>xmlagg</primary>
</indexterm>
<synopsis>
<function>xmlagg</function> ( <type>xml</type> ) <returnvalue>xml</returnvalue>
</synopsis>
<para>
The function <function>xmlagg</function> is, unlike the other
functions described here, an aggregate function. It concatenates the
input values to the aggregate function call,
much like <function>xmlconcat</function> does, except that concatenation
occurs across rows rather than across expressions in a single row.
See <xref linkend="functions-aggregate"/> for additional information
about aggregate functions.
</para>
<para>
Example:
<screen><![CDATA[
CREATE TABLE test (y int, x xml);
INSERT INTO test VALUES (1, '<foo>abc</foo>');
INSERT INTO test VALUES (2, '<bar/>');
SELECT xmlagg(x) FROM test;
xmlagg
----------------------
<foo>abc</foo><bar/>
]]></screen>
</para>
<para>
To determine the order of the concatenation, an <literal>ORDER BY</literal>
clause may be added to the aggregate call as described in
<xref linkend="syntax-aggregates"/>. For example:
<screen><![CDATA[
SELECT xmlagg(x ORDER BY y DESC) FROM test;
xmlagg
----------------------
<bar/><foo>abc</foo>
]]></screen>
</para>
<para>
The following non-standard approach used to be recommended
in previous versions, and may still be useful in specific
cases:
<screen><![CDATA[
SELECT xmlagg(x) FROM (SELECT * FROM test ORDER BY y DESC) AS tab;
xmlagg
----------------------
<bar/><foo>abc</foo>
]]></screen>
</para>
</sect3>
</sect2>
<sect2 id="functions-xml-predicates">
<title>XML Predicates</title>
<para>
The expressions described in this section check properties
of <type>xml</type> values.
</para>
<sect3>
<title><literal>IS DOCUMENT</literal></title>
<indexterm>
<primary>IS DOCUMENT</primary>
</indexterm>
<synopsis>
<type>xml</type> <literal>IS DOCUMENT</literal> <returnvalue>boolean</returnvalue>
</synopsis>
<para>
The expression <literal>IS DOCUMENT</literal> returns true if the
argument XML value is a proper XML document, false if it is not
(that is, it is a content fragment), or null if the argument is
null. See <xref linkend="datatype-xml"/> about the difference
between documents and content fragments.
</para>
</sect3>
<sect3>
<title><literal>IS NOT DOCUMENT</literal></title>
<indexterm>
<primary>IS NOT DOCUMENT</primary>
</indexterm>
<synopsis>
<type>xml</type> <literal>IS NOT DOCUMENT</literal> <returnvalue>boolean</returnvalue>
</synopsis>
<para>
The expression <literal>IS NOT DOCUMENT</literal> returns false if the
argument XML value is a proper XML document, true if it is not (that is,
it is a content fragment), or null if the argument is null.
</para>
</sect3>
<sect3 id="xml-exists">
<title><literal>XMLEXISTS</literal></title>
<indexterm>
<primary>XMLEXISTS</primary>
</indexterm>
<synopsis>
<function>XMLEXISTS</function> ( <type>text</type> <literal>PASSING</literal> <optional><literal>BY</literal> {<literal>REF</literal>|<literal>VALUE</literal>}</optional> <type>xml</type> <optional><literal>BY</literal> {<literal>REF</literal>|<literal>VALUE</literal>}</optional> ) <returnvalue>boolean</returnvalue>
</synopsis>
<para>
The function <function>xmlexists</function> evaluates an XPath 1.0
expression (the first argument), with the passed XML value as its context
item. The function returns false if the result of that evaluation
yields an empty node-set, true if it yields any other value. The
function returns null if any argument is null. A nonnull value
passed as the context item must be an XML document, not a content
fragment or any non-XML value.
</para>
<para>
Example:
<screen><![CDATA[
SELECT xmlexists('//town[text() = ''Toronto'']' PASSING BY VALUE '<towns><town>Toronto</town><town>Ottawa</town></towns>');
xmlexists
------------
t
(1 row)
]]></screen>
</para>
<para>
The <literal>BY REF</literal> and <literal>BY VALUE</literal> clauses
are accepted in <productname>PostgreSQL</productname>, but are ignored,
as discussed in <xref linkend="functions-xml-limits-postgresql"/>.
</para>
<para>
In the SQL standard, the <function>xmlexists</function> function
evaluates an expression in the XML Query language,
but <productname>PostgreSQL</productname> allows only an XPath 1.0
expression, as discussed in
<xref linkend="functions-xml-limits-xpath1"/>.
</para>
</sect3>
<sect3 id="xml-is-well-formed">
<title><literal>xml_is_well_formed</literal></title>
<indexterm>
<primary>xml_is_well_formed</primary>
</indexterm>
<indexterm>
<primary>xml_is_well_formed_document</primary>
</indexterm>
<indexterm>
<primary>xml_is_well_formed_content</primary>
</indexterm>
<synopsis>
<function>xml_is_well_formed</function> ( <type>text</type> ) <returnvalue>boolean</returnvalue>
<function>xml_is_well_formed_document</function> ( <type>text</type> ) <returnvalue>boolean</returnvalue>
<function>xml_is_well_formed_content</function> ( <type>text</type> ) <returnvalue>boolean</returnvalue>
</synopsis>
<para>
These functions check whether a <type>text</type> string represents
well-formed XML, returning a Boolean result.
<function>xml_is_well_formed_document</function> checks for a well-formed
document, while <function>xml_is_well_formed_content</function> checks
for well-formed content. <function>xml_is_well_formed</function> does
the former if the <xref linkend="guc-xmloption"/> configuration
parameter is set to <literal>DOCUMENT</literal>, or the latter if it is set to
<literal>CONTENT</literal>. This means that
<function>xml_is_well_formed</function> is useful for seeing whether
a simple cast to type <type>xml</type> will succeed, whereas the other two
functions are useful for seeing whether the corresponding variants of
<function>XMLPARSE</function> will succeed.
</para>
<para>
Examples:
<screen><![CDATA[
SET xmloption TO DOCUMENT;
SELECT xml_is_well_formed('<>');
xml_is_well_formed
--------------------
f
(1 row)
SELECT xml_is_well_formed('<abc/>');
xml_is_well_formed
--------------------
t
(1 row)
SET xmloption TO CONTENT;
SELECT xml_is_well_formed('abc');
xml_is_well_formed
--------------------
t
(1 row)
SELECT xml_is_well_formed_document('<pg:foo xmlns:pg="http://postgresql.org/stuff">bar</pg:foo>');
xml_is_well_formed_document
-----------------------------
t
(1 row)
SELECT xml_is_well_formed_document('<pg:foo xmlns:pg="http://postgresql.org/stuff">bar</my:foo>');
xml_is_well_formed_document
-----------------------------
f
(1 row)
]]></screen>
The last example shows that the checks include whether
namespaces are correctly matched.
</para>
</sect3>
</sect2>
<sect2 id="functions-xml-processing">
<title>Processing XML</title>
<para>
To process values of data type <type>xml</type>, PostgreSQL offers
the functions <function>xpath</function> and
<function>xpath_exists</function>, which evaluate XPath 1.0
expressions, and the <function>XMLTABLE</function>
table function.
</para>
<sect3 id="functions-xml-processing-xpath">
<title><literal>xpath</literal></title>
<indexterm>
<primary>XPath</primary>
</indexterm>
<synopsis>
<function>xpath</function> ( <parameter>xpath</parameter> <type>text</type>, <parameter>xml</parameter> <type>xml</type> <optional>, <parameter>nsarray</parameter> <type>text[]</type> </optional> ) <returnvalue>xml[]</returnvalue>
</synopsis>
<para>
The function <function>xpath</function> evaluates the XPath 1.0
expression <parameter>xpath</parameter> (given as text)
against the XML value
<parameter>xml</parameter>. It returns an array of XML values
corresponding to the node-set produced by the XPath expression.
If the XPath expression returns a scalar value rather than a node-set,
a single-element array is returned.
</para>
<para>
The second argument must be a well formed XML document. In particular,
it must have a single root node element.
</para>
<para>
The optional third argument of the function is an array of namespace
mappings. This array should be a two-dimensional <type>text</type> array with
the length of the second axis being equal to 2 (i.e., it should be an
array of arrays, each of which consists of exactly 2 elements).
The first element of each array entry is the namespace name (alias), the
second the namespace URI. It is not required that aliases provided in
this array be the same as those being used in the XML document itself (in
other words, both in the XML document and in the <function>xpath</function>
function context, aliases are <emphasis>local</emphasis>).
</para>
<para>
Example:
<screen><![CDATA[
SELECT xpath('/my:a/text()', '<my:a xmlns:my="http://example.com">test</my:a>',
ARRAY[ARRAY['my', 'http://example.com']]);
xpath
--------
{test}
(1 row)
]]></screen>
</para>
<para>
To deal with default (anonymous) namespaces, do something like this:
<screen><![CDATA[
SELECT xpath('//mydefns:b/text()', '<a xmlns="http://example.com"><b>test</b></a>',
ARRAY[ARRAY['mydefns', 'http://example.com']]);
xpath
--------
{test}
(1 row)
]]></screen>
</para>
</sect3>
<sect3 id="functions-xml-processing-xpath-exists">
<title><literal>xpath_exists</literal></title>
<indexterm>
<primary>xpath_exists</primary>
</indexterm>
<synopsis>
<function>xpath_exists</function> ( <parameter>xpath</parameter> <type>text</type>, <parameter>xml</parameter> <type>xml</type> <optional>, <parameter>nsarray</parameter> <type>text[]</type> </optional> ) <returnvalue>boolean</returnvalue>
</synopsis>
<para>
The function <function>xpath_exists</function> is a specialized form
of the <function>xpath</function> function. Instead of returning the
individual XML values that satisfy the XPath 1.0 expression, this function
returns a Boolean indicating whether the query was satisfied or not
(specifically, whether it produced any value other than an empty node-set).
This function is equivalent to the <literal>XMLEXISTS</literal> predicate,
except that it also offers support for a namespace mapping argument.
</para>
<para>
Example:
<screen><![CDATA[
SELECT xpath_exists('/my:a/text()', '<my:a xmlns:my="http://example.com">test</my:a>',
ARRAY[ARRAY['my', 'http://example.com']]);
xpath_exists
--------------
t
(1 row)
]]></screen>
</para>
</sect3>
<sect3 id="functions-xml-processing-xmltable">
<title><literal>xmltable</literal></title>
<indexterm>
<primary>xmltable</primary>
</indexterm>
<indexterm zone="functions-xml-processing-xmltable">
<primary>table function</primary>
<secondary>XMLTABLE</secondary>
</indexterm>
<synopsis>
<function>XMLTABLE</function> (
<optional> <literal>XMLNAMESPACES</literal> ( <replaceable>namespace_uri</replaceable> <literal>AS</literal> <replaceable>namespace_name</replaceable> <optional>, ...</optional> ), </optional>
<replaceable>row_expression</replaceable> <literal>PASSING</literal> <optional><literal>BY</literal> {<literal>REF</literal>|<literal>VALUE</literal>}</optional> <replaceable>document_expression</replaceable> <optional><literal>BY</literal> {<literal>REF</literal>|<literal>VALUE</literal>}</optional>
<literal>COLUMNS</literal> <replaceable>name</replaceable> { <replaceable>type</replaceable> <optional><literal>PATH</literal> <replaceable>column_expression</replaceable></optional> <optional><literal>DEFAULT</literal> <replaceable>default_expression</replaceable></optional> <optional><literal>NOT NULL</literal> | <literal>NULL</literal></optional>
| <literal>FOR ORDINALITY</literal> }
<optional>, ...</optional>
) <returnvalue>setof record</returnvalue>
</synopsis>
<para>
The <function>xmltable</function> expression produces a table based
on an XML value, an XPath filter to extract rows, and a
set of column definitions.
Although it syntactically resembles a function, it can only appear
as a table in a query's <literal>FROM</literal> clause.
</para>
<para>
The optional <literal>XMLNAMESPACES</literal> clause gives a
comma-separated list of namespace definitions, where
each <replaceable>namespace_uri</replaceable> is a <type>text</type>
expression and each <replaceable>namespace_name</replaceable> is a simple
identifier. It specifies the XML namespaces used in the document and
their aliases. A default namespace specification is not currently
supported.
</para>
<para>
The required <replaceable>row_expression</replaceable> argument is an
XPath 1.0 expression (given as <type>text</type>) that is evaluated,
passing the XML value <replaceable>document_expression</replaceable> as
its context item, to obtain a set of XML nodes. These nodes are what
<function>xmltable</function> transforms into output rows. No rows
will be produced if the <replaceable>document_expression</replaceable>
is null, nor if the <replaceable>row_expression</replaceable> produces
an empty node-set or any value other than a node-set.
</para>
<para>
<replaceable>document_expression</replaceable> provides the context
item for the <replaceable>row_expression</replaceable>. It must be a
well-formed XML document; fragments/forests are not accepted.
The <literal>BY REF</literal> and <literal>BY VALUE</literal> clauses
are accepted but ignored, as discussed in
<xref linkend="functions-xml-limits-postgresql"/>.
</para>
<para>
In the SQL standard, the <function>xmltable</function> function
evaluates expressions in the XML Query language,
but <productname>PostgreSQL</productname> allows only XPath 1.0
expressions, as discussed in
<xref linkend="functions-xml-limits-xpath1"/>.
</para>
<para>
The required <literal>COLUMNS</literal> clause specifies the
column(s) that will be produced in the output table.
See the syntax summary above for the format.
A name is required for each column, as is a data type
(unless <literal>FOR ORDINALITY</literal> is specified, in which case
type <type>integer</type> is implicit). The path, default and
nullability clauses are optional.
</para>
<para>
A column marked <literal>FOR ORDINALITY</literal> will be populated
with row numbers, starting with 1, in the order of nodes retrieved from
the <replaceable>row_expression</replaceable>'s result node-set.
At most one column may be marked <literal>FOR ORDINALITY</literal>.
</para>
<note>
<para>
XPath 1.0 does not specify an order for nodes in a node-set, so code
that relies on a particular order of the results will be
implementation-dependent. Details can be found in
<xref linkend="xml-xpath-1-specifics"/>.
</para>
</note>
<para>
The <replaceable>column_expression</replaceable> for a column is an
XPath 1.0 expression that is evaluated for each row, with the current
node from the <replaceable>row_expression</replaceable> result as its
context item, to find the value of the column. If
no <replaceable>column_expression</replaceable> is given, then the
column name is used as an implicit path.
</para>
<para>
If a column's XPath expression returns a non-XML value (which is limited
to string, boolean, or double in XPath 1.0) and the column has a
PostgreSQL type other than <type>xml</type>, the column will be set
as if by assigning the value's string representation to the PostgreSQL
type. (If the value is a boolean, its string representation is taken
to be <literal>1</literal> or <literal>0</literal> if the output
column's type category is numeric, otherwise <literal>true</literal> or
<literal>false</literal>.)
</para>
<para>
If a column's XPath expression returns a non-empty set of XML nodes
and the column's PostgreSQL type is <type>xml</type>, the column will
be assigned the expression result exactly, if it is of document or
content form.
<footnote>
<para>
A result containing more than one element node at the top level, or
non-whitespace text outside of an element, is an example of content form.
An XPath result can be of neither form, for example if it returns an
attribute node selected from the element that contains it. Such a result
will be put into content form with each such disallowed node replaced by
its string value, as defined for the XPath 1.0
<function>string</function> function.
</para>
</footnote>
</para>
<para>
A non-XML result assigned to an <type>xml</type> output column produces
content, a single text node with the string value of the result.
An XML result assigned to a column of any other type may not have more than
one node, or an error is raised. If there is exactly one node, the column
will be set as if by assigning the node's string
value (as defined for the XPath 1.0 <function>string</function> function)
to the PostgreSQL type.
</para>
<para>
The string value of an XML element is the concatenation, in document order,
of all text nodes contained in that element and its descendants. The string
value of an element with no descendant text nodes is an
empty string (not <literal>NULL</literal>).
Any <literal>xsi:nil</literal> attributes are ignored.
Note that the whitespace-only <literal>text()</literal> node between two non-text
elements is preserved, and that leading whitespace on a <literal>text()</literal>
node is not flattened.
The XPath 1.0 <function>string</function> function may be consulted for the
rules defining the string value of other XML node types and non-XML values.
</para>
<para>
The conversion rules presented here are not exactly those of the SQL
standard, as discussed in <xref linkend="functions-xml-limits-casts"/>.
</para>
<para>
If the path expression returns an empty node-set
(typically, when it does not match)
for a given row, the column will be set to <literal>NULL</literal>, unless
a <replaceable>default_expression</replaceable> is specified; then the
value resulting from evaluating that expression is used.
</para>
<para>
A <replaceable>default_expression</replaceable>, rather than being
evaluated immediately when <function>xmltable</function> is called,
is evaluated each time a default is needed for the column.
If the expression qualifies as stable or immutable, the repeat
evaluation may be skipped.
This means that you can usefully use volatile functions like
<function>nextval</function> in
<replaceable>default_expression</replaceable>.
</para>
<para>
Columns may be marked <literal>NOT NULL</literal>. If the
<replaceable>column_expression</replaceable> for a <literal>NOT
NULL</literal> column does not match anything and there is
no <literal>DEFAULT</literal> or
the <replaceable>default_expression</replaceable> also evaluates to null,
an error is reported.
</para>
<para>
Examples:
<screen><![CDATA[
CREATE TABLE xmldata AS SELECT
xml $$
<ROWS>
<ROW id="1">
<COUNTRY_ID>AU</COUNTRY_ID>
<COUNTRY_NAME>Australia</COUNTRY_NAME>
</ROW>
<ROW id="5">
<COUNTRY_ID>JP</COUNTRY_ID>
<COUNTRY_NAME>Japan</COUNTRY_NAME>
<PREMIER_NAME>Shinzo Abe</PREMIER_NAME>
<SIZE unit="sq_mi">145935</SIZE>
</ROW>
<ROW id="6">
<COUNTRY_ID>SG</COUNTRY_ID>
<COUNTRY_NAME>Singapore</COUNTRY_NAME>
<SIZE unit="sq_km">697</SIZE>
</ROW>
</ROWS>
$$ AS data;
SELECT xmltable.*
FROM xmldata,
XMLTABLE('//ROWS/ROW'
PASSING data
COLUMNS id int PATH '@id',
ordinality FOR ORDINALITY,
"COUNTRY_NAME" text,
country_id text PATH 'COUNTRY_ID',
size_sq_km float PATH 'SIZE[@unit = "sq_km"]',
size_other text PATH
'concat(SIZE[@unit!="sq_km"], " ", SIZE[@unit!="sq_km"]/@unit)',
premier_name text PATH 'PREMIER_NAME' DEFAULT 'not specified');
id | ordinality | COUNTRY_NAME | country_id | size_sq_km | size_other | premier_name
----+------------+--------------+------------+------------+--------------+---------------
1 | 1 | Australia | AU | | | not specified
5 | 2 | Japan | JP | | 145935 sq_mi | Shinzo Abe
6 | 3 | Singapore | SG | 697 | | not specified
]]></screen>
The following example shows concatenation of multiple text() nodes,
usage of the column name as XPath filter, and the treatment of whitespace,
XML comments and processing instructions:
<screen><![CDATA[
CREATE TABLE xmlelements AS SELECT
xml $$
<root>
<element> Hello<!-- xyxxz -->2a2<?aaaaa?> <!--x--> bbb<x>xxx</x>CC </element>
</root>
$$ AS data;
SELECT xmltable.*
FROM xmlelements, XMLTABLE('/root' PASSING data COLUMNS element text);
element
-------------------------
Hello2a2 bbbxxxCC
]]></screen>
</para>
<para>
The following example illustrates how
the <literal>XMLNAMESPACES</literal> clause can be used to specify
a list of namespaces
used in the XML document as well as in the XPath expressions:
<screen><![CDATA[
WITH xmldata(data) AS (VALUES ('
<example xmlns="http://example.com/myns" xmlns:B="http://example.com/b">
<item foo="1" B:bar="2"/>
<item foo="3" B:bar="4"/>
<item foo="4" B:bar="5"/>
</example>'::xml)
)
SELECT xmltable.*
FROM XMLTABLE(XMLNAMESPACES('http://example.com/myns' AS x,
'http://example.com/b' AS "B"),
'/x:example/x:item'
PASSING (SELECT data FROM xmldata)
COLUMNS foo int PATH '@foo',
bar int PATH '@B:bar');
foo | bar
-----+-----
1 | 2
3 | 4
4 | 5
(3 rows)
]]></screen>
</para>
</sect3>
</sect2>
<sect2 id="functions-xml-mapping">
<title>Mapping Tables to XML</title>
<indexterm zone="functions-xml-mapping">
<primary>XML export</primary>
</indexterm>
<para>
The following functions map the contents of relational tables to
XML values. They can be thought of as XML export functionality:
<synopsis>
<function>table_to_xml</function> ( <parameter>table</parameter> <type>regclass</type>, <parameter>nulls</parameter> <type>boolean</type>,
<parameter>tableforest</parameter> <type>boolean</type>, <parameter>targetns</parameter> <type>text</type> ) <returnvalue>xml</returnvalue>
<function>query_to_xml</function> ( <parameter>query</parameter> <type>text</type>, <parameter>nulls</parameter> <type>boolean</type>,
<parameter>tableforest</parameter> <type>boolean</type>, <parameter>targetns</parameter> <type>text</type> ) <returnvalue>xml</returnvalue>
<function>cursor_to_xml</function> ( <parameter>cursor</parameter> <type>refcursor</type>, <parameter>count</parameter> <type>integer</type>, <parameter>nulls</parameter> <type>boolean</type>,
<parameter>tableforest</parameter> <type>boolean</type>, <parameter>targetns</parameter> <type>text</type> ) <returnvalue>xml</returnvalue>
</synopsis>
</para>
<para>
<function>table_to_xml</function> maps the content of the named
table, passed as parameter <parameter>table</parameter>. The
<type>regclass</type> type accepts strings identifying tables using the
usual notation, including optional schema qualification and
double quotes (see <xref linkend="datatype-oid"/> for details).
<function>query_to_xml</function> executes the
query whose text is passed as parameter
<parameter>query</parameter> and maps the result set.
<function>cursor_to_xml</function> fetches the indicated number of
rows from the cursor specified by the parameter
<parameter>cursor</parameter>. This variant is recommended if
large tables have to be mapped, because the result value is built
up in memory by each function.
</para>
<para>
If <parameter>tableforest</parameter> is false, then the resulting
XML document looks like this:
<screen><![CDATA[
<tablename>
<row>
<columnname1>data</columnname1>
<columnname2>data</columnname2>
</row>
<row>
...
</row>
...
</tablename>
]]></screen>
If <parameter>tableforest</parameter> is true, the result is an
XML content fragment that looks like this:
<screen><![CDATA[
<tablename>
<columnname1>data</columnname1>
<columnname2>data</columnname2>
</tablename>
<tablename>
...
</tablename>
...
]]></screen>
If no table name is available, that is, when mapping a query or a
cursor, the string <literal>table</literal> is used in the first
format, <literal>row</literal> in the second format.
</para>
<para>
The choice between these formats is up to the user. The first
format is a proper XML document, which will be important in many
applications. The second format tends to be more useful in the
<function>cursor_to_xml</function> function if the result values are to be
reassembled into one document later on. The functions for
producing XML content discussed above, in particular
<function>xmlelement</function>, can be used to alter the results
to taste.
</para>
<para>
The data values are mapped in the same way as described for the
function <function>xmlelement</function> above.
</para>
<para>
The parameter <parameter>nulls</parameter> determines whether null
values should be included in the output. If true, null values in
columns are represented as:
<screen><![CDATA[
<columnname xsi:nil="true"/>
]]></screen>
where <literal>xsi</literal> is the XML namespace prefix for XML
Schema Instance. An appropriate namespace declaration will be
added to the result value. If false, columns containing null
values are simply omitted from the output.
</para>
<para>
The parameter <parameter>targetns</parameter> specifies the
desired XML namespace of the result. If no particular namespace
is wanted, an empty string should be passed.
</para>
<para>
The following functions return XML Schema documents describing the
mappings performed by the corresponding functions above:
<synopsis>
<function>table_to_xmlschema</function> ( <parameter>table</parameter> <type>regclass</type>, <parameter>nulls</parameter> <type>boolean</type>,
<parameter>tableforest</parameter> <type>boolean</type>, <parameter>targetns</parameter> <type>text</type> ) <returnvalue>xml</returnvalue>
<function>query_to_xmlschema</function> ( <parameter>query</parameter> <type>text</type>, <parameter>nulls</parameter> <type>boolean</type>,
<parameter>tableforest</parameter> <type>boolean</type>, <parameter>targetns</parameter> <type>text</type> ) <returnvalue>xml</returnvalue>
<function>cursor_to_xmlschema</function> ( <parameter>cursor</parameter> <type>refcursor</type>, <parameter>nulls</parameter> <type>boolean</type>,
<parameter>tableforest</parameter> <type>boolean</type>, <parameter>targetns</parameter> <type>text</type> ) <returnvalue>xml</returnvalue>
</synopsis>
It is essential that the same parameters are passed in order to
obtain matching XML data mappings and XML Schema documents.
</para>
<para>
The following functions produce XML data mappings and the
corresponding XML Schema in one document (or forest), linked
together. They can be useful where self-contained and
self-describing results are wanted:
<synopsis>
<function>table_to_xml_and_xmlschema</function> ( <parameter>table</parameter> <type>regclass</type>, <parameter>nulls</parameter> <type>boolean</type>,
<parameter>tableforest</parameter> <type>boolean</type>, <parameter>targetns</parameter> <type>text</type> ) <returnvalue>xml</returnvalue>
<function>query_to_xml_and_xmlschema</function> ( <parameter>query</parameter> <type>text</type>, <parameter>nulls</parameter> <type>boolean</type>,
<parameter>tableforest</parameter> <type>boolean</type>, <parameter>targetns</parameter> <type>text</type> ) <returnvalue>xml</returnvalue>
</synopsis>
</para>
<para>
In addition, the following functions are available to produce
analogous mappings of entire schemas or the entire current
database:
<synopsis>
<function>schema_to_xml</function> ( <parameter>schema</parameter> <type>name</type>, <parameter>nulls</parameter> <type>boolean</type>,
<parameter>tableforest</parameter> <type>boolean</type>, <parameter>targetns</parameter> <type>text</type> ) <returnvalue>xml</returnvalue>
<function>schema_to_xmlschema</function> ( <parameter>schema</parameter> <type>name</type>, <parameter>nulls</parameter> <type>boolean</type>,
<parameter>tableforest</parameter> <type>boolean</type>, <parameter>targetns</parameter> <type>text</type> ) <returnvalue>xml</returnvalue>
<function>schema_to_xml_and_xmlschema</function> ( <parameter>schema</parameter> <type>name</type>, <parameter>nulls</parameter> <type>boolean</type>,
<parameter>tableforest</parameter> <type>boolean</type>, <parameter>targetns</parameter> <type>text</type> ) <returnvalue>xml</returnvalue>
<function>database_to_xml</function> ( <parameter>nulls</parameter> <type>boolean</type>,
<parameter>tableforest</parameter> <type>boolean</type>, <parameter>targetns</parameter> <type>text</type> ) <returnvalue>xml</returnvalue>
<function>database_to_xmlschema</function> ( <parameter>nulls</parameter> <type>boolean</type>,
<parameter>tableforest</parameter> <type>boolean</type>, <parameter>targetns</parameter> <type>text</type> ) <returnvalue>xml</returnvalue>
<function>database_to_xml_and_xmlschema</function> ( <parameter>nulls</parameter> <type>boolean</type>,
<parameter>tableforest</parameter> <type>boolean</type>, <parameter>targetns</parameter> <type>text</type> ) <returnvalue>xml</returnvalue>
</synopsis>
These functions ignore tables that are not readable by the current user.
The database-wide functions additionally ignore schemas that the current
user does not have <literal>USAGE</literal> (lookup) privilege for.
</para>
<para>
Note that these potentially produce a lot of data, which needs to
be built up in memory. When requesting content mappings of large
schemas or databases, it might be worthwhile to consider mapping the
tables separately instead, possibly even through a cursor.
</para>
<para>
The result of a schema content mapping looks like this:
<screen><![CDATA[
<schemaname>
table1-mapping
table2-mapping
...
</schemaname>]]></screen>
where the format of a table mapping depends on the
<parameter>tableforest</parameter> parameter as explained above.
</para>
<para>
The result of a database content mapping looks like this:
<screen><![CDATA[
<dbname>
<schema1name>
...
</schema1name>
<schema2name>
...
</schema2name>
...
</dbname>]]></screen>
where the schema mapping is as above.
</para>
<para>
As an example of using the output produced by these functions,
<xref linkend="xslt-xml-html"/> shows an XSLT stylesheet that
converts the output of
<function>table_to_xml_and_xmlschema</function> to an HTML
document containing a tabular rendition of the table data. In a
similar manner, the results from these functions can be
converted into other XML-based formats.
</para>
<example id="xslt-xml-html">
<title>XSLT Stylesheet for Converting SQL/XML Output to HTML</title>
<programlisting><![CDATA[
<?xml version="1.0"?>
<xsl:stylesheet version="1.0"
xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
xmlns:xsd="http://www.w3.org/2001/XMLSchema"
xmlns="http://www.w3.org/1999/xhtml"
>
<xsl:output method="xml"
doctype-system="http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd"
doctype-public="-//W3C/DTD XHTML 1.0 Strict//EN"
indent="yes"/>
<xsl:template match="/*">
<xsl:variable name="schema" select="//xsd:schema"/>
<xsl:variable name="tabletypename"
select="$schema/xsd:element[@name=name(current())]/@type"/>
<xsl:variable name="rowtypename"
select="$schema/xsd:complexType[@name=$tabletypename]/xsd:sequence/xsd:element[@name='row']/@type"/>
<html>
<head>
<title><xsl:value-of select="name(current())"/></title>
</head>
<body>
<table>
<tr>
<xsl:for-each select="$schema/xsd:complexType[@name=$rowtypename]/xsd:sequence/xsd:element/@name">
<th><xsl:value-of select="."/></th>
</xsl:for-each>
</tr>
<xsl:for-each select="row">
<tr>
<xsl:for-each select="*">
<td><xsl:value-of select="."/></td>
</xsl:for-each>
</tr>
</xsl:for-each>
</table>
</body>
</html>
</xsl:template>
</xsl:stylesheet>
]]></programlisting>
</example>
</sect2>
</sect1>
<sect1 id="functions-json">
<title>JSON Functions and Operators</title>
<indexterm zone="functions-json">
<primary>JSON</primary>
<secondary>functions and operators</secondary>
</indexterm>
<para>
This section describes:
<itemizedlist>
<listitem>
<para>
functions and operators for processing and creating JSON data
</para>
</listitem>
<listitem>
<para>
the SQL/JSON path language
</para>
</listitem>
</itemizedlist>
</para>
<para>
To learn more about the SQL/JSON standard, see
<xref linkend="sqltr-19075-6"/>. For details on JSON types
supported in <productname>PostgreSQL</productname>,
see <xref linkend="datatype-json"/>.
</para>
<sect2 id="functions-json-processing">
<title>Processing and Creating JSON Data</title>
<para>
<xref linkend="functions-json-op-table"/> shows the operators that
are available for use with JSON data types (see <xref
linkend="datatype-json"/>).
In addition, the usual comparison operators shown in <xref
linkend="functions-comparison-op-table"/> are available for
<type>jsonb</type>, though not for <type>json</type>. The comparison
operators follow the ordering rules for B-tree operations outlined in
<xref linkend="json-indexing"/>.
</para>
<table id="functions-json-op-table">
<title><type>json</type> and <type>jsonb</type> Operators</title>
<tgroup cols="1">
<thead>
<row>
<entry role="func_table_entry"><para role="func_signature">
Operator
</para>
<para>
Description
</para>
<para>
Example(s)
</para></entry>
</row>
</thead>
<tbody>
<row>
<entry role="func_table_entry"><para role="func_signature">
<type>json</type> <literal>-></literal> <type>integer</type>
<returnvalue>json</returnvalue>
</para>
<para role="func_signature">
<type>jsonb</type> <literal>-></literal> <type>integer</type>
<returnvalue>jsonb</returnvalue>
</para>
<para>
Extracts <parameter>n</parameter>'th element of JSON array
(array elements are indexed from zero, but negative integers count
from the end).
</para>
<para>
<literal>'[{"a":"foo"},{"b":"bar"},{"c":"baz"}]'::json -> 2</literal>
<returnvalue>{"c":"baz"}</returnvalue>
</para>
<para>
<literal>'[{"a":"foo"},{"b":"bar"},{"c":"baz"}]'::json -> -3</literal>
<returnvalue>{"a":"foo"}</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<type>json</type> <literal>-></literal> <type>text</type>
<returnvalue>json</returnvalue>
</para>
<para role="func_signature">
<type>jsonb</type> <literal>-></literal> <type>text</type>
<returnvalue>jsonb</returnvalue>
</para>
<para>
Extracts JSON object field with the given key.
</para>
<para>
<literal>'{"a": {"b":"foo"}}'::json -> 'a'</literal>
<returnvalue>{"b":"foo"}</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<type>json</type> <literal>->></literal> <type>integer</type>
<returnvalue>text</returnvalue>
</para>
<para role="func_signature">
<type>jsonb</type> <literal>->></literal> <type>integer</type>
<returnvalue>text</returnvalue>
</para>
<para>
Extracts <parameter>n</parameter>'th element of JSON array,
as <type>text</type>.
</para>
<para>
<literal>'[1,2,3]'::json ->> 2</literal>
<returnvalue>3</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<type>json</type> <literal>->></literal> <type>text</type>
<returnvalue>text</returnvalue>
</para>
<para role="func_signature">
<type>jsonb</type> <literal>->></literal> <type>text</type>
<returnvalue>text</returnvalue>
</para>
<para>
Extracts JSON object field with the given key, as <type>text</type>.
</para>
<para>
<literal>'{"a":1,"b":2}'::json ->> 'b'</literal>
<returnvalue>2</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<type>json</type> <literal>#></literal> <type>text[]</type>
<returnvalue>json</returnvalue>
</para>
<para role="func_signature">
<type>jsonb</type> <literal>#></literal> <type>text[]</type>
<returnvalue>jsonb</returnvalue>
</para>
<para>
Extracts JSON sub-object at the specified path, where path elements
can be either field keys or array indexes.
</para>
<para>
<literal>'{"a": {"b": ["foo","bar"]}}'::json #> '{a,b,1}'</literal>
<returnvalue>"bar"</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<type>json</type> <literal>#>></literal> <type>text[]</type>
<returnvalue>text</returnvalue>
</para>
<para role="func_signature">
<type>jsonb</type> <literal>#>></literal> <type>text[]</type>
<returnvalue>text</returnvalue>
</para>
<para>
Extracts JSON sub-object at the specified path as <type>text</type>.
</para>
<para>
<literal>'{"a": {"b": ["foo","bar"]}}'::json #>> '{a,b,1}'</literal>
<returnvalue>bar</returnvalue>
</para></entry>
</row>
</tbody>
</tgroup>
</table>
<note>
<para>
The field/element/path extraction operators return NULL, rather than
failing, if the JSON input does not have the right structure to match
the request; for example if no such key or array element exists.
</para>
</note>
<para>
Some further operators exist only for <type>jsonb</type>, as shown
in <xref linkend="functions-jsonb-op-table"/>.
<xref linkend="json-indexing"/>
describes how these operators can be used to effectively search indexed
<type>jsonb</type> data.
</para>
<table id="functions-jsonb-op-table">
<title>Additional <type>jsonb</type> Operators</title>
<tgroup cols="1">
<thead>
<row>
<entry role="func_table_entry"><para role="func_signature">
Operator
</para>
<para>
Description
</para>
<para>
Example(s)
</para></entry>
</row>
</thead>
<tbody>
<row>
<entry role="func_table_entry"><para role="func_signature">
<type>jsonb</type> <literal>@></literal> <type>jsonb</type>
<returnvalue>boolean</returnvalue>
</para>
<para>
Does the first JSON value contain the second?
(See <xref linkend="json-containment"/> for details about containment.)
</para>
<para>
<literal>'{"a":1, "b":2}'::jsonb @> '{"b":2}'::jsonb</literal>
<returnvalue>t</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<type>jsonb</type> <literal><@</literal> <type>jsonb</type>
<returnvalue>boolean</returnvalue>
</para>
<para>
Is the first JSON value contained in the second?
</para>
<para>
<literal>'{"b":2}'::jsonb <@ '{"a":1, "b":2}'::jsonb</literal>
<returnvalue>t</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<type>jsonb</type> <literal>?</literal> <type>text</type>
<returnvalue>boolean</returnvalue>
</para>
<para>
Does the text string exist as a top-level key or array element within
the JSON value?
</para>
<para>
<literal>'{"a":1, "b":2}'::jsonb ? 'b'</literal>
<returnvalue>t</returnvalue>
</para>
<para>
<literal>'["a", "b", "c"]'::jsonb ? 'b'</literal>
<returnvalue>t</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<type>jsonb</type> <literal>?|</literal> <type>text[]</type>
<returnvalue>boolean</returnvalue>
</para>
<para>
Do any of the strings in the text array exist as top-level keys or
array elements?
</para>
<para>
<literal>'{"a":1, "b":2, "c":3}'::jsonb ?| array['b', 'd']</literal>
<returnvalue>t</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<type>jsonb</type> <literal>?&</literal> <type>text[]</type>
<returnvalue>boolean</returnvalue>
</para>
<para>
Do all of the strings in the text array exist as top-level keys or
array elements?
</para>
<para>
<literal>'["a", "b", "c"]'::jsonb ?& array['a', 'b']</literal>
<returnvalue>t</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<type>jsonb</type> <literal>||</literal> <type>jsonb</type>
<returnvalue>jsonb</returnvalue>
</para>
<para>
Concatenates two <type>jsonb</type> values.
Concatenating two arrays generates an array containing all the
elements of each input. Concatenating two objects generates an
object containing the union of their
keys, taking the second object's value when there are duplicate keys.
All other cases are treated by converting a non-array input into a
single-element array, and then proceeding as for two arrays.
Does not operate recursively: only the top-level array or object
structure is merged.
</para>
<para>
<literal>'["a", "b"]'::jsonb || '["a", "d"]'::jsonb</literal>
<returnvalue>["a", "b", "a", "d"]</returnvalue>
</para>
<para>
<literal>'{"a": "b"}'::jsonb || '{"c": "d"}'::jsonb</literal>
<returnvalue>{"a": "b", "c": "d"}</returnvalue>
</para>
<para>
<literal>'[1, 2]'::jsonb || '3'::jsonb</literal>
<returnvalue>[1, 2, 3]</returnvalue>
</para>
<para>
<literal>'{"a": "b"}'::jsonb || '42'::jsonb</literal>
<returnvalue>[{"a": "b"}, 42]</returnvalue>
</para>
<para>
To append an array to another array as a single entry, wrap it
in an additional layer of array, for example:
</para>
<para>
<literal>'[1, 2]'::jsonb || jsonb_build_array('[3, 4]'::jsonb)</literal>
<returnvalue>[1, 2, [3, 4]]</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<type>jsonb</type> <literal>-</literal> <type>text</type>
<returnvalue>jsonb</returnvalue>
</para>
<para>
Deletes a key (and its value) from a JSON object, or matching string
value(s) from a JSON array.
</para>
<para>
<literal>'{"a": "b", "c": "d"}'::jsonb - 'a'</literal>
<returnvalue>{"c": "d"}</returnvalue>
</para>
<para>
<literal>'["a", "b", "c", "b"]'::jsonb - 'b'</literal>
<returnvalue>["a", "c"]</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<type>jsonb</type> <literal>-</literal> <type>text[]</type>
<returnvalue>jsonb</returnvalue>
</para>
<para>
Deletes all matching keys or array elements from the left operand.
</para>
<para>
<literal>'{"a": "b", "c": "d"}'::jsonb - '{a,c}'::text[]</literal>
<returnvalue>{}</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<type>jsonb</type> <literal>-</literal> <type>integer</type>
<returnvalue>jsonb</returnvalue>
</para>
<para>
Deletes the array element with specified index (negative
integers count from the end). Throws an error if JSON value
is not an array.
</para>
<para>
<literal>'["a", "b"]'::jsonb - 1 </literal>
<returnvalue>["a"]</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<type>jsonb</type> <literal>#-</literal> <type>text[]</type>
<returnvalue>jsonb</returnvalue>
</para>
<para>
Deletes the field or array element at the specified path, where path
elements can be either field keys or array indexes.
</para>
<para>
<literal>'["a", {"b":1}]'::jsonb #- '{1,b}'</literal>
<returnvalue>["a", {}]</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<type>jsonb</type> <literal>@?</literal> <type>jsonpath</type>
<returnvalue>boolean</returnvalue>
</para>
<para>
Does JSON path return any item for the specified JSON value?
</para>
<para>
<literal>'{"a":[1,2,3,4,5]}'::jsonb @? '$.a[*] ? (@ > 2)'</literal>
<returnvalue>t</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<type>jsonb</type> <literal>@@</literal> <type>jsonpath</type>
<returnvalue>boolean</returnvalue>
</para>
<para>
Returns the result of a JSON path predicate check for the
specified JSON value. Only the first item of the result is taken into
account. If the result is not Boolean, then <literal>NULL</literal>
is returned.
</para>
<para>
<literal>'{"a":[1,2,3,4,5]}'::jsonb @@ '$.a[*] > 2'</literal>
<returnvalue>t</returnvalue>
</para></entry>
</row>
</tbody>
</tgroup>
</table>
<note>
<para>
The <type>jsonpath</type> operators <literal>@?</literal>
and <literal>@@</literal> suppress the following errors: missing object
field or array element, unexpected JSON item type, datetime and numeric
errors. The <type>jsonpath</type>-related functions described below can
also be told to suppress these types of errors. This behavior might be
helpful when searching JSON document collections of varying structure.
</para>
</note>
<para>
<xref linkend="functions-json-creation-table"/> shows the functions that are
available for constructing <type>json</type> and <type>jsonb</type> values.
</para>
<table id="functions-json-creation-table">
<title>JSON Creation Functions</title>
<tgroup cols="1">
<thead>
<row>
<entry role="func_table_entry"><para role="func_signature">
Function
</para>
<para>
Description
</para>
<para>
Example(s)
</para></entry>
</row>
</thead>
<tbody>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>to_json</primary>
</indexterm>
<function>to_json</function> ( <type>anyelement</type> )
<returnvalue>json</returnvalue>
</para>
<para role="func_signature">
<indexterm>
<primary>to_jsonb</primary>
</indexterm>
<function>to_jsonb</function> ( <type>anyelement</type> )
<returnvalue>jsonb</returnvalue>
</para>
<para>
Converts any SQL value to <type>json</type> or <type>jsonb</type>.
Arrays and composites are converted recursively to arrays and
objects (multidimensional arrays become arrays of arrays in JSON).
Otherwise, if there is a cast from the SQL data type
to <type>json</type>, the cast function will be used to perform the
conversion;<footnote>
<para>
For example, the <xref linkend="hstore"/> extension has a cast
from <type>hstore</type> to <type>json</type>, so that
<type>hstore</type> values converted via the JSON creation functions
will be represented as JSON objects, not as primitive string values.
</para>
</footnote>
otherwise, a scalar JSON value is produced. For any scalar other than
a number, a Boolean, or a null value, the text representation will be
used, with escaping as necessary to make it a valid JSON string value.
</para>
<para>
<literal>to_json('Fred said "Hi."'::text)</literal>
<returnvalue>"Fred said \"Hi.\""</returnvalue>
</para>
<para>
<literal>to_jsonb(row(42, 'Fred said "Hi."'::text))</literal>
<returnvalue>{"f1": 42, "f2": "Fred said \"Hi.\""}</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>array_to_json</primary>
</indexterm>
<function>array_to_json</function> ( <type>anyarray</type> <optional>, <type>boolean</type> </optional> )
<returnvalue>json</returnvalue>
</para>
<para>
Converts an SQL array to a JSON array. The behavior is the same
as <function>to_json</function> except that line feeds will be added
between top-level array elements if the optional boolean parameter is
true.
</para>
<para>
<literal>array_to_json('{{1,5},{99,100}}'::int[])</literal>
<returnvalue>[[1,5],[99,100]]</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>row_to_json</primary>
</indexterm>
<function>row_to_json</function> ( <type>record</type> <optional>, <type>boolean</type> </optional> )
<returnvalue>json</returnvalue>
</para>
<para>
Converts an SQL composite value to a JSON object. The behavior is the
same as <function>to_json</function> except that line feeds will be
added between top-level elements if the optional boolean parameter is
true.
</para>
<para>
<literal>row_to_json(row(1,'foo'))</literal>
<returnvalue>{"f1":1,"f2":"foo"}</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>json_build_array</primary>
</indexterm>
<function>json_build_array</function> ( <literal>VARIADIC</literal> <type>"any"</type> )
<returnvalue>json</returnvalue>
</para>
<para role="func_signature">
<indexterm>
<primary>jsonb_build_array</primary>
</indexterm>
<function>jsonb_build_array</function> ( <literal>VARIADIC</literal> <type>"any"</type> )
<returnvalue>jsonb</returnvalue>
</para>
<para>
Builds a possibly-heterogeneously-typed JSON array out of a variadic
argument list. Each argument is converted as
per <function>to_json</function> or <function>to_jsonb</function>.
</para>
<para>
<literal>json_build_array(1, 2, 'foo', 4, 5)</literal>
<returnvalue>[1, 2, "foo", 4, 5]</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>json_build_object</primary>
</indexterm>
<function>json_build_object</function> ( <literal>VARIADIC</literal> <type>"any"</type> )
<returnvalue>json</returnvalue>
</para>
<para role="func_signature">
<indexterm>
<primary>jsonb_build_object</primary>
</indexterm>
<function>jsonb_build_object</function> ( <literal>VARIADIC</literal> <type>"any"</type> )
<returnvalue>jsonb</returnvalue>
</para>
<para>
Builds a JSON object out of a variadic argument list. By convention,
the argument list consists of alternating keys and values. Key
arguments are coerced to text; value arguments are converted as
per <function>to_json</function> or <function>to_jsonb</function>.
</para>
<para>
<literal>json_build_object('foo', 1, 2, row(3,'bar'))</literal>
<returnvalue>{"foo" : 1, "2" : {"f1":3,"f2":"bar"}}</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>json_object</primary>
</indexterm>
<function>json_object</function> ( <type>text[]</type> )
<returnvalue>json</returnvalue>
</para>
<para role="func_signature">
<indexterm>
<primary>jsonb_object</primary>
</indexterm>
<function>jsonb_object</function> ( <type>text[]</type> )
<returnvalue>jsonb</returnvalue>
</para>
<para>
Builds a JSON object out of a text array. The array must have either
exactly one dimension with an even number of members, in which case
they are taken as alternating key/value pairs, or two dimensions
such that each inner array has exactly two elements, which
are taken as a key/value pair. All values are converted to JSON
strings.
</para>
<para>
<literal>json_object('{a, 1, b, "def", c, 3.5}')</literal>
<returnvalue>{"a" : "1", "b" : "def", "c" : "3.5"}</returnvalue>
</para>
<para><literal>json_object('{{a, 1}, {b, "def"}, {c, 3.5}}')</literal>
<returnvalue>{"a" : "1", "b" : "def", "c" : "3.5"}</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<function>json_object</function> ( <parameter>keys</parameter> <type>text[]</type>, <parameter>values</parameter> <type>text[]</type> )
<returnvalue>json</returnvalue>
</para>
<para role="func_signature">
<function>jsonb_object</function> ( <parameter>keys</parameter> <type>text[]</type>, <parameter>values</parameter> <type>text[]</type> )
<returnvalue>jsonb</returnvalue>
</para>
<para>
This form of <function>json_object</function> takes keys and values
pairwise from separate text arrays. Otherwise it is identical to
the one-argument form.
</para>
<para>
<literal>json_object('{a,b}', '{1,2}')</literal>
<returnvalue>{"a": "1", "b": "2"}</returnvalue>
</para></entry>
</row>
</tbody>
</tgroup>
</table>
<para>
<xref linkend="functions-json-processing-table"/> shows the functions that
are available for processing <type>json</type> and <type>jsonb</type> values.
</para>
<table id="functions-json-processing-table">
<title>JSON Processing Functions</title>
<tgroup cols="1">
<thead>
<row>
<entry role="func_table_entry"><para role="func_signature">
Function
</para>
<para>
Description
</para>
<para>
Example(s)
</para></entry>
</row>
</thead>
<tbody>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>json_array_elements</primary>
</indexterm>
<function>json_array_elements</function> ( <type>json</type> )
<returnvalue>setof json</returnvalue>
</para>
<para role="func_signature">
<indexterm>
<primary>jsonb_array_elements</primary>
</indexterm>
<function>jsonb_array_elements</function> ( <type>jsonb</type> )
<returnvalue>setof jsonb</returnvalue>
</para>
<para>
Expands the top-level JSON array into a set of JSON values.
</para>
<para>
<literal>select * from json_array_elements('[1,true, [2,false]]')</literal>
<returnvalue></returnvalue>
<programlisting>
value
-----------
1
true
[2,false]
</programlisting>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>json_array_elements_text</primary>
</indexterm>
<function>json_array_elements_text</function> ( <type>json</type> )
<returnvalue>setof text</returnvalue>
</para>
<para role="func_signature">
<indexterm>
<primary>jsonb_array_elements_text</primary>
</indexterm>
<function>jsonb_array_elements_text</function> ( <type>jsonb</type> )
<returnvalue>setof text</returnvalue>
</para>
<para>
Expands the top-level JSON array into a set of <type>text</type> values.
</para>
<para>
<literal>select * from json_array_elements_text('["foo", "bar"]')</literal>
<returnvalue></returnvalue>
<programlisting>
value
-----------
foo
bar
</programlisting>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>json_array_length</primary>
</indexterm>
<function>json_array_length</function> ( <type>json</type> )
<returnvalue>integer</returnvalue>
</para>
<para role="func_signature">
<indexterm>
<primary>jsonb_array_length</primary>
</indexterm>
<function>jsonb_array_length</function> ( <type>jsonb</type> )
<returnvalue>integer</returnvalue>
</para>
<para>
Returns the number of elements in the top-level JSON array.
</para>
<para>
<literal>json_array_length('[1,2,3,{"f1":1,"f2":[5,6]},4]')</literal>
<returnvalue>5</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>json_each</primary>
</indexterm>
<function>json_each</function> ( <type>json</type> )
<returnvalue>setof record</returnvalue>
( <parameter>key</parameter> <type>text</type>,
<parameter>value</parameter> <type>json</type> )
</para>
<para role="func_signature">
<indexterm>
<primary>jsonb_each</primary>
</indexterm>
<function>jsonb_each</function> ( <type>jsonb</type> )
<returnvalue>setof record</returnvalue>
( <parameter>key</parameter> <type>text</type>,
<parameter>value</parameter> <type>jsonb</type> )
</para>
<para>
Expands the top-level JSON object into a set of key/value pairs.
</para>
<para>
<literal>select * from json_each('{"a":"foo", "b":"bar"}')</literal>
<returnvalue></returnvalue>
<programlisting>
key | value
-----+-------
a | "foo"
b | "bar"
</programlisting>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>json_each_text</primary>
</indexterm>
<function>json_each_text</function> ( <type>json</type> )
<returnvalue>setof record</returnvalue>
( <parameter>key</parameter> <type>text</type>,
<parameter>value</parameter> <type>text</type> )
</para>
<para role="func_signature">
<indexterm>
<primary>jsonb_each_text</primary>
</indexterm>
<function>jsonb_each_text</function> ( <type>jsonb</type> )
<returnvalue>setof record</returnvalue>
( <parameter>key</parameter> <type>text</type>,
<parameter>value</parameter> <type>text</type> )
</para>
<para>
Expands the top-level JSON object into a set of key/value pairs.
The returned <parameter>value</parameter>s will be of
type <type>text</type>.
</para>
<para>
<literal>select * from json_each_text('{"a":"foo", "b":"bar"}')</literal>
<returnvalue></returnvalue>
<programlisting>
key | value
-----+-------
a | foo
b | bar
</programlisting>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>json_extract_path</primary>
</indexterm>
<function>json_extract_path</function> ( <parameter>from_json</parameter> <type>json</type>, <literal>VARIADIC</literal> <parameter>path_elems</parameter> <type>text[]</type> )
<returnvalue>json</returnvalue>
</para>
<para role="func_signature">
<indexterm>
<primary>jsonb_extract_path</primary>
</indexterm>
<function>jsonb_extract_path</function> ( <parameter>from_json</parameter> <type>jsonb</type>, <literal>VARIADIC</literal> <parameter>path_elems</parameter> <type>text[]</type> )
<returnvalue>jsonb</returnvalue>
</para>
<para>
Extracts JSON sub-object at the specified path.
(This is functionally equivalent to the <literal>#></literal>
operator, but writing the path out as a variadic list can be more
convenient in some cases.)
</para>
<para>
<literal>json_extract_path('{"f2":{"f3":1},"f4":{"f5":99,"f6":"foo"}}', 'f4', 'f6')</literal>
<returnvalue>"foo"</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>json_extract_path_text</primary>
</indexterm>
<function>json_extract_path_text</function> ( <parameter>from_json</parameter> <type>json</type>, <literal>VARIADIC</literal> <parameter>path_elems</parameter> <type>text[]</type> )
<returnvalue>text</returnvalue>
</para>
<para role="func_signature">
<indexterm>
<primary>jsonb_extract_path_text</primary>
</indexterm>
<function>jsonb_extract_path_text</function> ( <parameter>from_json</parameter> <type>jsonb</type>, <literal>VARIADIC</literal> <parameter>path_elems</parameter> <type>text[]</type> )
<returnvalue>text</returnvalue>
</para>
<para>
Extracts JSON sub-object at the specified path as <type>text</type>.
(This is functionally equivalent to the <literal>#>></literal>
operator.)
</para>
<para>
<literal>json_extract_path_text('{"f2":{"f3":1},"f4":{"f5":99,"f6":"foo"}}', 'f4', 'f6')</literal>
<returnvalue>foo</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>json_object_keys</primary>
</indexterm>
<function>json_object_keys</function> ( <type>json</type> )
<returnvalue>setof text</returnvalue>
</para>
<para role="func_signature">
<indexterm>
<primary>jsonb_object_keys</primary>
</indexterm>
<function>jsonb_object_keys</function> ( <type>jsonb</type> )
<returnvalue>setof text</returnvalue>
</para>
<para>
Returns the set of keys in the top-level JSON object.
</para>
<para>
<literal>select * from json_object_keys('{"f1":"abc","f2":{"f3":"a", "f4":"b"}}')</literal>
<returnvalue></returnvalue>
<programlisting>
json_object_keys
------------------
f1
f2
</programlisting>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>json_populate_record</primary>
</indexterm>
<function>json_populate_record</function> ( <parameter>base</parameter> <type>anyelement</type>, <parameter>from_json</parameter> <type>json</type> )
<returnvalue>anyelement</returnvalue>
</para>
<para role="func_signature">
<indexterm>
<primary>jsonb_populate_record</primary>
</indexterm>
<function>jsonb_populate_record</function> ( <parameter>base</parameter> <type>anyelement</type>, <parameter>from_json</parameter> <type>jsonb</type> )
<returnvalue>anyelement</returnvalue>
</para>
<para>
Expands the top-level JSON object to a row having the composite type
of the <parameter>base</parameter> argument. The JSON object
is scanned for fields whose names match column names of the output row
type, and their values are inserted into those columns of the output.
(Fields that do not correspond to any output column name are ignored.)
In typical use, the value of <parameter>base</parameter> is just
<literal>NULL</literal>, which means that any output columns that do
not match any object field will be filled with nulls. However,
if <parameter>base</parameter> isn't <literal>NULL</literal> then
the values it contains will be used for unmatched columns.
</para>
<para>
To convert a JSON value to the SQL type of an output column, the
following rules are applied in sequence:
<itemizedlist spacing="compact">
<listitem>
<para>
A JSON null value is converted to an SQL null in all cases.
</para>
</listitem>
<listitem>
<para>
If the output column is of type <type>json</type>
or <type>jsonb</type>, the JSON value is just reproduced exactly.
</para>
</listitem>
<listitem>
<para>
If the output column is a composite (row) type, and the JSON value
is a JSON object, the fields of the object are converted to columns
of the output row type by recursive application of these rules.
</para>
</listitem>
<listitem>
<para>
Likewise, if the output column is an array type and the JSON value
is a JSON array, the elements of the JSON array are converted to
elements of the output array by recursive application of these
rules.
</para>
</listitem>
<listitem>
<para>
Otherwise, if the JSON value is a string, the contents of the
string are fed to the input conversion function for the column's
data type.
</para>
</listitem>
<listitem>
<para>
Otherwise, the ordinary text representation of the JSON value is
fed to the input conversion function for the column's data type.
</para>
</listitem>
</itemizedlist>
</para>
<para>
While the example below uses a constant JSON value, typical use would
be to reference a <type>json</type> or <type>jsonb</type> column
laterally from another table in the query's <literal>FROM</literal>
clause. Writing <function>json_populate_record</function> in
the <literal>FROM</literal> clause is good practice, since all of the
extracted columns are available for use without duplicate function
calls.
</para>
<para>
<literal>create type subrowtype as (d int, e text);</literal>
<literal>create type myrowtype as (a int, b text[], c subrowtype);</literal>
</para>
<para>
<literal>select * from json_populate_record(null::myrowtype,
'{"a": 1, "b": ["2", "a b"], "c": {"d": 4, "e": "a b c"}, "x": "foo"}')</literal>
<returnvalue></returnvalue>
<programlisting>
a | b | c
---+-----------+-------------
1 | {2,"a b"} | (4,"a b c")
</programlisting>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>json_populate_recordset</primary>
</indexterm>
<function>json_populate_recordset</function> ( <parameter>base</parameter> <type>anyelement</type>, <parameter>from_json</parameter> <type>json</type> )
<returnvalue>setof anyelement</returnvalue>
</para>
<para role="func_signature">
<indexterm>
<primary>jsonb_populate_recordset</primary>
</indexterm>
<function>jsonb_populate_recordset</function> ( <parameter>base</parameter> <type>anyelement</type>, <parameter>from_json</parameter> <type>jsonb</type> )
<returnvalue>setof anyelement</returnvalue>
</para>
<para>
Expands the top-level JSON array of objects to a set of rows having
the composite type of the <parameter>base</parameter> argument.
Each element of the JSON array is processed as described above
for <function>json[b]_populate_record</function>.
</para>
<para>
<literal>create type twoints as (a int, b int);</literal>
</para>
<para>
<literal>select * from json_populate_recordset(null::twoints, '[{"a":1,"b":2}, {"a":3,"b":4}]')</literal>
<returnvalue></returnvalue>
<programlisting>
a | b
---+---
1 | 2
3 | 4
</programlisting>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>json_to_record</primary>
</indexterm>
<function>json_to_record</function> ( <type>json</type> )
<returnvalue>record</returnvalue>
</para>
<para role="func_signature">
<indexterm>
<primary>jsonb_to_record</primary>
</indexterm>
<function>jsonb_to_record</function> ( <type>jsonb</type> )
<returnvalue>record</returnvalue>
</para>
<para>
Expands the top-level JSON object to a row having the composite type
defined by an <literal>AS</literal> clause. (As with all functions
returning <type>record</type>, the calling query must explicitly
define the structure of the record with an <literal>AS</literal>
clause.) The output record is filled from fields of the JSON object,
in the same way as described above
for <function>json[b]_populate_record</function>. Since there is no
input record value, unmatched columns are always filled with nulls.
</para>
<para>
<literal>create type myrowtype as (a int, b text);</literal>
</para>
<para>
<literal>select * from json_to_record('{"a":1,"b":[1,2,3],"c":[1,2,3],"e":"bar","r": {"a": 123, "b": "a b c"}}') as x(a int, b text, c int[], d text, r myrowtype)</literal>
<returnvalue></returnvalue>
<programlisting>
a | b | c | d | r
---+---------+---------+---+---------------
1 | [1,2,3] | {1,2,3} | | (123,"a b c")
</programlisting>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>json_to_recordset</primary>
</indexterm>
<function>json_to_recordset</function> ( <type>json</type> )
<returnvalue>setof record</returnvalue>
</para>
<para role="func_signature">
<indexterm>
<primary>jsonb_to_recordset</primary>
</indexterm>
<function>jsonb_to_recordset</function> ( <type>jsonb</type> )
<returnvalue>setof record</returnvalue>
</para>
<para>
Expands the top-level JSON array of objects to a set of rows having
the composite type defined by an <literal>AS</literal> clause. (As
with all functions returning <type>record</type>, the calling query
must explicitly define the structure of the record with
an <literal>AS</literal> clause.) Each element of the JSON array is
processed as described above
for <function>json[b]_populate_record</function>.
</para>
<para>
<literal>select * from json_to_recordset('[{"a":1,"b":"foo"}, {"a":"2","c":"bar"}]') as x(a int, b text)</literal>
<returnvalue></returnvalue>
<programlisting>
a | b
---+-----
1 | foo
2 |
</programlisting>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>jsonb_set</primary>
</indexterm>
<function>jsonb_set</function> ( <parameter>target</parameter> <type>jsonb</type>, <parameter>path</parameter> <type>text[]</type>, <parameter>new_value</parameter> <type>jsonb</type> <optional>, <parameter>create_if_missing</parameter> <type>boolean</type> </optional> )
<returnvalue>jsonb</returnvalue>
</para>
<para>
Returns <parameter>target</parameter>
with the item designated by <parameter>path</parameter>
replaced by <parameter>new_value</parameter>, or with
<parameter>new_value</parameter> added if
<parameter>create_if_missing</parameter> is true (which is the
default) and the item designated by <parameter>path</parameter>
does not exist.
All earlier steps in the path must exist, or
the <parameter>target</parameter> is returned unchanged.
As with the path oriented operators, negative integers that
appear in the <parameter>path</parameter> count from the end
of JSON arrays.
If the last path step is an array index that is out of range,
and <parameter>create_if_missing</parameter> is true, the new
value is added at the beginning of the array if the index is negative,
or at the end of the array if it is positive.
</para>
<para>
<literal>jsonb_set('[{"f1":1,"f2":null},2,null,3]', '{0,f1}', '[2,3,4]', false)</literal>
<returnvalue>[{"f1": [2, 3, 4], "f2": null}, 2, null, 3]</returnvalue>
</para>
<para>
<literal>jsonb_set('[{"f1":1,"f2":null},2]', '{0,f3}', '[2,3,4]')</literal>
<returnvalue>[{"f1": 1, "f2": null, "f3": [2, 3, 4]}, 2]</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>jsonb_set_lax</primary>
</indexterm>
<function>jsonb_set_lax</function> ( <parameter>target</parameter> <type>jsonb</type>, <parameter>path</parameter> <type>text[]</type>, <parameter>new_value</parameter> <type>jsonb</type> <optional>, <parameter>create_if_missing</parameter> <type>boolean</type> <optional>, <parameter>null_value_treatment</parameter> <type>text</type> </optional></optional> )
<returnvalue>jsonb</returnvalue>
</para>
<para>
If <parameter>new_value</parameter> is not <literal>NULL</literal>,
behaves identically to <literal>jsonb_set</literal>. Otherwise behaves
according to the value
of <parameter>null_value_treatment</parameter> which must be one
of <literal>'raise_exception'</literal>,
<literal>'use_json_null'</literal>, <literal>'delete_key'</literal>, or
<literal>'return_target'</literal>. The default is
<literal>'use_json_null'</literal>.
</para>
<para>
<literal>jsonb_set_lax('[{"f1":1,"f2":null},2,null,3]', '{0,f1}', null)</literal>
<returnvalue>[{"f1":null,"f2":null},2,null,3]</returnvalue>
</para>
<para>
<literal>jsonb_set_lax('[{"f1":99,"f2":null},2]', '{0,f3}', null, true, 'return_target')</literal>
<returnvalue>[{"f1": 99, "f2": null}, 2]</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>jsonb_insert</primary>
</indexterm>
<function>jsonb_insert</function> ( <parameter>target</parameter> <type>jsonb</type>, <parameter>path</parameter> <type>text[]</type>, <parameter>new_value</parameter> <type>jsonb</type> <optional>, <parameter>insert_after</parameter> <type>boolean</type> </optional> )
<returnvalue>jsonb</returnvalue>
</para>
<para>
Returns <parameter>target</parameter>
with <parameter>new_value</parameter> inserted. If the item
designated by the <parameter>path</parameter> is an array
element, <parameter>new_value</parameter> will be inserted before
that item if <parameter>insert_after</parameter> is false (which
is the default), or after it
if <parameter>insert_after</parameter> is true. If the item
designated by the <parameter>path</parameter> is an object
field, <parameter>new_value</parameter> will be inserted only if
the object does not already contain that key.
All earlier steps in the path must exist, or
the <parameter>target</parameter> is returned unchanged.
As with the path oriented operators, negative integers that
appear in the <parameter>path</parameter> count from the end
of JSON arrays.
If the last path step is an array index that is out of range, the new
value is added at the beginning of the array if the index is negative,
or at the end of the array if it is positive.
</para>
<para>
<literal>jsonb_insert('{"a": [0,1,2]}', '{a, 1}', '"new_value"')</literal>
<returnvalue>{"a": [0, "new_value", 1, 2]}</returnvalue>
</para>
<para>
<literal>jsonb_insert('{"a": [0,1,2]}', '{a, 1}', '"new_value"', true)</literal>
<returnvalue>{"a": [0, 1, "new_value", 2]}</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>json_strip_nulls</primary>
</indexterm>
<function>json_strip_nulls</function> ( <type>json</type> )
<returnvalue>json</returnvalue>
</para>
<para role="func_signature">
<indexterm>
<primary>jsonb_strip_nulls</primary>
</indexterm>
<function>jsonb_strip_nulls</function> ( <type>jsonb</type> )
<returnvalue>jsonb</returnvalue>
</para>
<para>
Deletes all object fields that have null values from the given JSON
value, recursively. Null values that are not object fields are
untouched.
</para>
<para>
<literal>json_strip_nulls('[{"f1":1, "f2":null}, 2, null, 3]')</literal>
<returnvalue>[{"f1":1},2,null,3]</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>jsonb_path_exists</primary>
</indexterm>
<function>jsonb_path_exists</function> ( <parameter>target</parameter> <type>jsonb</type>, <parameter>path</parameter> <type>jsonpath</type> <optional>, <parameter>vars</parameter> <type>jsonb</type> <optional>, <parameter>silent</parameter> <type>boolean</type> </optional></optional> )
<returnvalue>boolean</returnvalue>
</para>
<para>
Checks whether the JSON path returns any item for the specified JSON
value.
If the <parameter>vars</parameter> argument is specified, it must
be a JSON object, and its fields provide named values to be
substituted into the <type>jsonpath</type> expression.
If the <parameter>silent</parameter> argument is specified and
is <literal>true</literal>, the function suppresses the same errors
as the <literal>@?</literal> and <literal>@@</literal> operators do.
</para>
<para>
<literal>jsonb_path_exists('{"a":[1,2,3,4,5]}', '$.a[*] ? (@ >= $min && @ <= $max)', '{"min":2, "max":4}')</literal>
<returnvalue>t</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>jsonb_path_match</primary>
</indexterm>
<function>jsonb_path_match</function> ( <parameter>target</parameter> <type>jsonb</type>, <parameter>path</parameter> <type>jsonpath</type> <optional>, <parameter>vars</parameter> <type>jsonb</type> <optional>, <parameter>silent</parameter> <type>boolean</type> </optional></optional> )
<returnvalue>boolean</returnvalue>
</para>
<para>
Returns the result of a JSON path predicate check for the specified
JSON value. Only the first item of the result is taken into account.
If the result is not Boolean, then <literal>NULL</literal> is returned.
The optional <parameter>vars</parameter>
and <parameter>silent</parameter> arguments act the same as
for <function>jsonb_path_exists</function>.
</para>
<para>
<literal>jsonb_path_match('{"a":[1,2,3,4,5]}', 'exists($.a[*] ? (@ >= $min && @ <= $max))', '{"min":2, "max":4}')</literal>
<returnvalue>t</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>jsonb_path_query</primary>
</indexterm>
<function>jsonb_path_query</function> ( <parameter>target</parameter> <type>jsonb</type>, <parameter>path</parameter> <type>jsonpath</type> <optional>, <parameter>vars</parameter> <type>jsonb</type> <optional>, <parameter>silent</parameter> <type>boolean</type> </optional></optional> )
<returnvalue>setof jsonb</returnvalue>
</para>
<para>
Returns all JSON items returned by the JSON path for the specified
JSON value.
The optional <parameter>vars</parameter>
and <parameter>silent</parameter> arguments act the same as
for <function>jsonb_path_exists</function>.
</para>
<para>
<literal>select * from jsonb_path_query('{"a":[1,2,3,4,5]}', '$.a[*] ? (@ >= $min && @ <= $max)', '{"min":2, "max":4}')</literal>
<returnvalue></returnvalue>
<programlisting>
jsonb_path_query
------------------
2
3
4
</programlisting>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>jsonb_path_query_array</primary>
</indexterm>
<function>jsonb_path_query_array</function> ( <parameter>target</parameter> <type>jsonb</type>, <parameter>path</parameter> <type>jsonpath</type> <optional>, <parameter>vars</parameter> <type>jsonb</type> <optional>, <parameter>silent</parameter> <type>boolean</type> </optional></optional> )
<returnvalue>jsonb</returnvalue>
</para>
<para>
Returns all JSON items returned by the JSON path for the specified
JSON value, as a JSON array.
The optional <parameter>vars</parameter>
and <parameter>silent</parameter> arguments act the same as
for <function>jsonb_path_exists</function>.
</para>
<para>
<literal>jsonb_path_query_array('{"a":[1,2,3,4,5]}', '$.a[*] ? (@ >= $min && @ <= $max)', '{"min":2, "max":4}')</literal>
<returnvalue>[2, 3, 4]</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>jsonb_path_query_first</primary>
</indexterm>
<function>jsonb_path_query_first</function> ( <parameter>target</parameter> <type>jsonb</type>, <parameter>path</parameter> <type>jsonpath</type> <optional>, <parameter>vars</parameter> <type>jsonb</type> <optional>, <parameter>silent</parameter> <type>boolean</type> </optional></optional> )
<returnvalue>jsonb</returnvalue>
</para>
<para>
Returns the first JSON item returned by the JSON path for the
specified JSON value. Returns <literal>NULL</literal> if there are no
results.
The optional <parameter>vars</parameter>
and <parameter>silent</parameter> arguments act the same as
for <function>jsonb_path_exists</function>.
</para>
<para>
<literal>jsonb_path_query_first('{"a":[1,2,3,4,5]}', '$.a[*] ? (@ >= $min && @ <= $max)', '{"min":2, "max":4}')</literal>
<returnvalue>2</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>jsonb_path_exists_tz</primary>
</indexterm>
<function>jsonb_path_exists_tz</function> ( <parameter>target</parameter> <type>jsonb</type>, <parameter>path</parameter> <type>jsonpath</type> <optional>, <parameter>vars</parameter> <type>jsonb</type> <optional>, <parameter>silent</parameter> <type>boolean</type> </optional></optional> )
<returnvalue>boolean</returnvalue>
</para>
<para role="func_signature">
<indexterm>
<primary>jsonb_path_match_tz</primary>
</indexterm>
<function>jsonb_path_match_tz</function> ( <parameter>target</parameter> <type>jsonb</type>, <parameter>path</parameter> <type>jsonpath</type> <optional>, <parameter>vars</parameter> <type>jsonb</type> <optional>, <parameter>silent</parameter> <type>boolean</type> </optional></optional> )
<returnvalue>boolean</returnvalue>
</para>
<para role="func_signature">
<indexterm>
<primary>jsonb_path_query_tz</primary>
</indexterm>
<function>jsonb_path_query_tz</function> ( <parameter>target</parameter> <type>jsonb</type>, <parameter>path</parameter> <type>jsonpath</type> <optional>, <parameter>vars</parameter> <type>jsonb</type> <optional>, <parameter>silent</parameter> <type>boolean</type> </optional></optional> )
<returnvalue>setof jsonb</returnvalue>
</para>
<para role="func_signature">
<indexterm>
<primary>jsonb_path_query_array_tz</primary>
</indexterm>
<function>jsonb_path_query_array_tz</function> ( <parameter>target</parameter> <type>jsonb</type>, <parameter>path</parameter> <type>jsonpath</type> <optional>, <parameter>vars</parameter> <type>jsonb</type> <optional>, <parameter>silent</parameter> <type>boolean</type> </optional></optional> )
<returnvalue>jsonb</returnvalue>
</para>
<para role="func_signature">
<indexterm>
<primary>jsonb_path_query_first_tz</primary>
</indexterm>
<function>jsonb_path_query_first_tz</function> ( <parameter>target</parameter> <type>jsonb</type>, <parameter>path</parameter> <type>jsonpath</type> <optional>, <parameter>vars</parameter> <type>jsonb</type> <optional>, <parameter>silent</parameter> <type>boolean</type> </optional></optional> )
<returnvalue>jsonb</returnvalue>
</para>
<para>
These functions act like their counterparts described above without
the <literal>_tz</literal> suffix, except that these functions support
comparisons of date/time values that require timezone-aware
conversions. The example below requires interpretation of the
date-only value <literal>2015-08-02</literal> as a timestamp with time
zone, so the result depends on the current
<xref linkend="guc-timezone"/> setting. Due to this dependency, these
functions are marked as stable, which means these functions cannot be
used in indexes. Their counterparts are immutable, and so can be used
in indexes; but they will throw errors if asked to make such
comparisons.
</para>
<para>
<literal>jsonb_path_exists_tz('["2015-08-01 12:00:00 -05"]', '$[*] ? (@.datetime() < "2015-08-02".datetime())')</literal>
<returnvalue>t</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>jsonb_pretty</primary>
</indexterm>
<function>jsonb_pretty</function> ( <type>jsonb</type> )
<returnvalue>text</returnvalue>
</para>
<para>
Converts the given JSON value to pretty-printed, indented text.
</para>
<para>
<literal>jsonb_pretty('[{"f1":1,"f2":null}, 2]')</literal>
<returnvalue></returnvalue>
<programlisting>
[
{
"f1": 1,
"f2": null
},
2
]
</programlisting>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>json_typeof</primary>
</indexterm>
<function>json_typeof</function> ( <type>json</type> )
<returnvalue>text</returnvalue>
</para>
<para role="func_signature">
<indexterm>
<primary>jsonb_typeof</primary>
</indexterm>
<function>jsonb_typeof</function> ( <type>jsonb</type> )
<returnvalue>text</returnvalue>
</para>
<para>
Returns the type of the top-level JSON value as a text string.
Possible types are
<literal>object</literal>, <literal>array</literal>,
<literal>string</literal>, <literal>number</literal>,
<literal>boolean</literal>, and <literal>null</literal>.
(The <literal>null</literal> result should not be confused
with an SQL NULL; see the examples.)
</para>
<para>
<literal>json_typeof('-123.4')</literal>
<returnvalue>number</returnvalue>
</para>
<para>
<literal>json_typeof('null'::json)</literal>
<returnvalue>null</returnvalue>
</para>
<para>
<literal>json_typeof(NULL::json) IS NULL</literal>
<returnvalue>t</returnvalue>
</para></entry>
</row>
</tbody>
</tgroup>
</table>
<para>
See also <xref linkend="functions-aggregate"/> for the aggregate
function <function>json_agg</function> which aggregates record
values as JSON, the aggregate function
<function>json_object_agg</function> which aggregates pairs of values
into a JSON object, and their <type>jsonb</type> equivalents,
<function>jsonb_agg</function> and <function>jsonb_object_agg</function>.
</para>
</sect2>
<sect2 id="functions-sqljson-path">
<title>The SQL/JSON Path Language</title>
<indexterm zone="functions-sqljson-path">
<primary>SQL/JSON path language</primary>
</indexterm>
<para>
SQL/JSON path expressions specify the items to be retrieved
from the JSON data, similar to XPath expressions used
for SQL access to XML. In <productname>PostgreSQL</productname>,
path expressions are implemented as the <type>jsonpath</type>
data type and can use any elements described in
<xref linkend="datatype-jsonpath"/>.
</para>
<para>
JSON query functions and operators
pass the provided path expression to the <firstterm>path engine</firstterm>
for evaluation. If the expression matches the queried JSON data,
the corresponding JSON item, or set of items, is returned.
Path expressions are written in the SQL/JSON path language
and can include arithmetic expressions and functions.
</para>
<para>
A path expression consists of a sequence of elements allowed
by the <type>jsonpath</type> data type.
The path expression is normally evaluated from left to right, but
you can use parentheses to change the order of operations.
If the evaluation is successful, a sequence of JSON items is produced,
and the evaluation result is returned to the JSON query function
that completes the specified computation.
</para>
<para>
To refer to the JSON value being queried (the
<firstterm>context item</firstterm>), use the <literal>$</literal> variable
in the path expression. It can be followed by one or more
<link linkend="type-jsonpath-accessors">accessor operators</link>,
which go down the JSON structure level by level to retrieve sub-items
of the context item. Each operator that follows deals with the
result of the previous evaluation step.
</para>
<para>
For example, suppose you have some JSON data from a GPS tracker that you
would like to parse, such as:
<programlisting>
{
"track": {
"segments": [
{
"location": [ 47.763, 13.4034 ],
"start time": "2018-10-14 10:05:14",
"HR": 73
},
{
"location": [ 47.706, 13.2635 ],
"start time": "2018-10-14 10:39:21",
"HR": 135
}
]
}
}
</programlisting>
</para>
<para>
To retrieve the available track segments, you need to use the
<literal>.<replaceable>key</replaceable></literal> accessor
operator to descend through surrounding JSON objects:
<programlisting>
$.track.segments
</programlisting>
</para>
<para>
To retrieve the contents of an array, you typically use the
<literal>[*]</literal> operator. For example,
the following path will return the location coordinates for all
the available track segments:
<programlisting>
$.track.segments[*].location
</programlisting>
</para>
<para>
To return the coordinates of the first segment only, you can
specify the corresponding subscript in the <literal>[]</literal>
accessor operator. Recall that JSON array indexes are 0-relative:
<programlisting>
$.track.segments[0].location
</programlisting>
</para>
<para>
The result of each path evaluation step can be processed
by one or more <type>jsonpath</type> operators and methods
listed in <xref linkend="functions-sqljson-path-operators"/>.
Each method name must be preceded by a dot. For example,
you can get the size of an array:
<programlisting>
$.track.segments.size()
</programlisting>
More examples of using <type>jsonpath</type> operators
and methods within path expressions appear below in
<xref linkend="functions-sqljson-path-operators"/>.
</para>
<para>
When defining a path, you can also use one or more
<firstterm>filter expressions</firstterm> that work similarly to the
<literal>WHERE</literal> clause in SQL. A filter expression begins with
a question mark and provides a condition in parentheses:
<programlisting>
? (<replaceable>condition</replaceable>)
</programlisting>
</para>
<para>
Filter expressions must be written just after the path evaluation step
to which they should apply. The result of that step is filtered to include
only those items that satisfy the provided condition. SQL/JSON defines
three-valued logic, so the condition can be <literal>true</literal>, <literal>false</literal>,
or <literal>unknown</literal>. The <literal>unknown</literal> value
plays the same role as SQL <literal>NULL</literal> and can be tested
for with the <literal>is unknown</literal> predicate. Further path
evaluation steps use only those items for which the filter expression
returned <literal>true</literal>.
</para>
<para>
The functions and operators that can be used in filter expressions are
listed in <xref linkend="functions-sqljson-filter-ex-table"/>. Within a
filter expression, the <literal>@</literal> variable denotes the value
being filtered (i.e., one result of the preceding path step). You can
write accessor operators after <literal>@</literal> to retrieve component
items.
</para>
<para>
For example, suppose you would like to retrieve all heart rate values higher
than 130. You can achieve this using the following expression:
<programlisting>
$.track.segments[*].HR ? (@ > 130)
</programlisting>
</para>
<para>
To get the start times of segments with such values, you have to
filter out irrelevant segments before returning the start times, so the
filter expression is applied to the previous step, and the path used
in the condition is different:
<programlisting>
$.track.segments[*] ? (@.HR > 130)."start time"
</programlisting>
</para>
<para>
You can use several filter expressions in sequence, if required. For
example, the following expression selects start times of all segments that
contain locations with relevant coordinates and high heart rate values:
<programlisting>
$.track.segments[*] ? (@.location[1] < 13.4) ? (@.HR > 130)."start time"
</programlisting>
</para>
<para>
Using filter expressions at different nesting levels is also allowed.
The following example first filters all segments by location, and then
returns high heart rate values for these segments, if available:
<programlisting>
$.track.segments[*] ? (@.location[1] < 13.4).HR ? (@ > 130)
</programlisting>
</para>
<para>
You can also nest filter expressions within each other:
<programlisting>
$.track ? (exists(@.segments[*] ? (@.HR > 130))).segments.size()
</programlisting>
This expression returns the size of the track if it contains any
segments with high heart rate values, or an empty sequence otherwise.
</para>
<para>
<productname>PostgreSQL</productname>'s implementation of the SQL/JSON path
language has the following deviations from the SQL/JSON standard:
</para>
<itemizedlist>
<listitem>
<para>
A path expression can be a Boolean predicate, although the SQL/JSON
standard allows predicates only in filters. This is necessary for
implementation of the <literal>@@</literal> operator. For example,
the following <type>jsonpath</type> expression is valid in
<productname>PostgreSQL</productname>:
<programlisting>
$.track.segments[*].HR < 70
</programlisting>
</para>
</listitem>
<listitem>
<para>
There are minor differences in the interpretation of regular
expression patterns used in <literal>like_regex</literal> filters, as
described in <xref linkend="jsonpath-regular-expressions"/>.
</para>
</listitem>
</itemizedlist>
<sect3 id="strict-and-lax-modes">
<title>Strict and Lax Modes</title>
<para>
When you query JSON data, the path expression may not match the
actual JSON data structure. An attempt to access a non-existent
member of an object or element of an array results in a
structural error. SQL/JSON path expressions have two modes
of handling structural errors:
</para>
<itemizedlist>
<listitem>
<para>
lax (default) — the path engine implicitly adapts
the queried data to the specified path.
Any remaining structural errors are suppressed and converted
to empty SQL/JSON sequences.
</para>
</listitem>
<listitem>
<para>
strict — if a structural error occurs, an error is raised.
</para>
</listitem>
</itemizedlist>
<para>
The lax mode facilitates matching of a JSON document structure and path
expression if the JSON data does not conform to the expected schema.
If an operand does not match the requirements of a particular operation,
it can be automatically wrapped as an SQL/JSON array or unwrapped by
converting its elements into an SQL/JSON sequence before performing
this operation. Besides, comparison operators automatically unwrap their
operands in the lax mode, so you can compare SQL/JSON arrays
out-of-the-box. An array of size 1 is considered equal to its sole element.
Automatic unwrapping is not performed only when:
<itemizedlist>
<listitem>
<para>
The path expression contains <literal>type()</literal> or
<literal>size()</literal> methods that return the type
and the number of elements in the array, respectively.
</para>
</listitem>
<listitem>
<para>
The queried JSON data contain nested arrays. In this case, only
the outermost array is unwrapped, while all the inner arrays
remain unchanged. Thus, implicit unwrapping can only go one
level down within each path evaluation step.
</para>
</listitem>
</itemizedlist>
</para>
<para>
For example, when querying the GPS data listed above, you can
abstract from the fact that it stores an array of segments
when using the lax mode:
<programlisting>
lax $.track.segments.location
</programlisting>
</para>
<para>
In the strict mode, the specified path must exactly match the structure of
the queried JSON document to return an SQL/JSON item, so using this
path expression will cause an error. To get the same result as in
the lax mode, you have to explicitly unwrap the
<literal>segments</literal> array:
<programlisting>
strict $.track.segments[*].location
</programlisting>
</para>
<para>
The <literal>.**</literal> accessor can lead to surprising results
when using the lax mode. For instance, the following query selects every
<literal>HR</literal> value twice:
<programlisting>
lax $.**.HR
</programlisting>
This happens because the <literal>.**</literal> accessor selects both
the <literal>segments</literal> array and each of its elements, while
the <literal>.HR</literal> accessor automatically unwraps arrays when
using the lax mode. To avoid surprising results, we recommend using
the <literal>.**</literal> accessor only in the strict mode. The
following query selects each <literal>HR</literal> value just once:
<programlisting>
strict $.**.HR
</programlisting>
</para>
</sect3>
<sect3 id="functions-sqljson-path-operators">
<title>SQL/JSON Path Operators and Methods</title>
<para>
<xref linkend="functions-sqljson-op-table"/> shows the operators and
methods available in <type>jsonpath</type>. Note that while the unary
operators and methods can be applied to multiple values resulting from a
preceding path step, the binary operators (addition etc.) can only be
applied to single values.
</para>
<table id="functions-sqljson-op-table">
<title><type>jsonpath</type> Operators and Methods</title>
<tgroup cols="1">
<thead>
<row>
<entry role="func_table_entry"><para role="func_signature">
Operator/Method
</para>
<para>
Description
</para>
<para>
Example(s)
</para></entry>
</row>
</thead>
<tbody>
<row>
<entry role="func_table_entry"><para role="func_signature">
<replaceable>number</replaceable> <literal>+</literal> <replaceable>number</replaceable>
<returnvalue><replaceable>number</replaceable></returnvalue>
</para>
<para>
Addition
</para>
<para>
<literal>jsonb_path_query('[2]', '$[0] + 3')</literal>
<returnvalue>5</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<literal>+</literal> <replaceable>number</replaceable>
<returnvalue><replaceable>number</replaceable></returnvalue>
</para>
<para>
Unary plus (no operation); unlike addition, this can iterate over
multiple values
</para>
<para>
<literal>jsonb_path_query_array('{"x": [2,3,4]}', '+ $.x')</literal>
<returnvalue>[2, 3, 4]</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<replaceable>number</replaceable> <literal>-</literal> <replaceable>number</replaceable>
<returnvalue><replaceable>number</replaceable></returnvalue>
</para>
<para>
Subtraction
</para>
<para>
<literal>jsonb_path_query('[2]', '7 - $[0]')</literal>
<returnvalue>5</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<literal>-</literal> <replaceable>number</replaceable>
<returnvalue><replaceable>number</replaceable></returnvalue>
</para>
<para>
Negation; unlike subtraction, this can iterate over
multiple values
</para>
<para>
<literal>jsonb_path_query_array('{"x": [2,3,4]}', '- $.x')</literal>
<returnvalue>[-2, -3, -4]</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<replaceable>number</replaceable> <literal>*</literal> <replaceable>number</replaceable>
<returnvalue><replaceable>number</replaceable></returnvalue>
</para>
<para>
Multiplication
</para>
<para>
<literal>jsonb_path_query('[4]', '2 * $[0]')</literal>
<returnvalue>8</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<replaceable>number</replaceable> <literal>/</literal> <replaceable>number</replaceable>
<returnvalue><replaceable>number</replaceable></returnvalue>
</para>
<para>
Division
</para>
<para>
<literal>jsonb_path_query('[8.5]', '$[0] / 2')</literal>
<returnvalue>4.2500000000000000</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<replaceable>number</replaceable> <literal>%</literal> <replaceable>number</replaceable>
<returnvalue><replaceable>number</replaceable></returnvalue>
</para>
<para>
Modulo (remainder)
</para>
<para>
<literal>jsonb_path_query('[32]', '$[0] % 10')</literal>
<returnvalue>2</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<replaceable>value</replaceable> <literal>.</literal> <literal>type()</literal>
<returnvalue><replaceable>string</replaceable></returnvalue>
</para>
<para>
Type of the JSON item (see <function>json_typeof</function>)
</para>
<para>
<literal>jsonb_path_query_array('[1, "2", {}]', '$[*].type()')</literal>
<returnvalue>["number", "string", "object"]</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<replaceable>value</replaceable> <literal>.</literal> <literal>size()</literal>
<returnvalue><replaceable>number</replaceable></returnvalue>
</para>
<para>
Size of the JSON item (number of array elements, or 1 if not an
array)
</para>
<para>
<literal>jsonb_path_query('{"m": [11, 15]}', '$.m.size()')</literal>
<returnvalue>2</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<replaceable>value</replaceable> <literal>.</literal> <literal>double()</literal>
<returnvalue><replaceable>number</replaceable></returnvalue>
</para>
<para>
Approximate floating-point number converted from a JSON number or
string
</para>
<para>
<literal>jsonb_path_query('{"len": "1.9"}', '$.len.double() * 2')</literal>
<returnvalue>3.8</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<replaceable>number</replaceable> <literal>.</literal> <literal>ceiling()</literal>
<returnvalue><replaceable>number</replaceable></returnvalue>
</para>
<para>
Nearest integer greater than or equal to the given number
</para>
<para>
<literal>jsonb_path_query('{"h": 1.3}', '$.h.ceiling()')</literal>
<returnvalue>2</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<replaceable>number</replaceable> <literal>.</literal> <literal>floor()</literal>
<returnvalue><replaceable>number</replaceable></returnvalue>
</para>
<para>
Nearest integer less than or equal to the given number
</para>
<para>
<literal>jsonb_path_query('{"h": 1.7}', '$.h.floor()')</literal>
<returnvalue>1</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<replaceable>number</replaceable> <literal>.</literal> <literal>abs()</literal>
<returnvalue><replaceable>number</replaceable></returnvalue>
</para>
<para>
Absolute value of the given number
</para>
<para>
<literal>jsonb_path_query('{"z": -0.3}', '$.z.abs()')</literal>
<returnvalue>0.3</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<replaceable>string</replaceable> <literal>.</literal> <literal>datetime()</literal>
<returnvalue><replaceable>datetime_type</replaceable></returnvalue>
(see note)
</para>
<para>
Date/time value converted from a string
</para>
<para>
<literal>jsonb_path_query('["2015-8-1", "2015-08-12"]', '$[*] ? (@.datetime() < "2015-08-2".datetime())')</literal>
<returnvalue>"2015-8-1"</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<replaceable>string</replaceable> <literal>.</literal> <literal>datetime(<replaceable>template</replaceable>)</literal>
<returnvalue><replaceable>datetime_type</replaceable></returnvalue>
(see note)
</para>
<para>
Date/time value converted from a string using the
specified <function>to_timestamp</function> template
</para>
<para>
<literal>jsonb_path_query_array('["12:30", "18:40"]', '$[*].datetime("HH24:MI")')</literal>
<returnvalue>["12:30:00", "18:40:00"]</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<replaceable>object</replaceable> <literal>.</literal> <literal>keyvalue()</literal>
<returnvalue><replaceable>array</replaceable></returnvalue>
</para>
<para>
The object's key-value pairs, represented as an array of objects
containing three fields: <literal>"key"</literal>,
<literal>"value"</literal>, and <literal>"id"</literal>;
<literal>"id"</literal> is a unique identifier of the object the
key-value pair belongs to
</para>
<para>
<literal>jsonb_path_query_array('{"x": "20", "y": 32}', '$.keyvalue()')</literal>
<returnvalue>[{"id": 0, "key": "x", "value": "20"}, {"id": 0, "key": "y", "value": 32}]</returnvalue>
</para></entry>
</row>
</tbody>
</tgroup>
</table>
<note>
<para>
The result type of the <literal>datetime()</literal> and
<literal>datetime(<replaceable>template</replaceable>)</literal>
methods can be <type>date</type>, <type>timetz</type>, <type>time</type>,
<type>timestamptz</type>, or <type>timestamp</type>.
Both methods determine their result type dynamically.
</para>
<para>
The <literal>datetime()</literal> method sequentially tries to
match its input string to the ISO formats
for <type>date</type>, <type>timetz</type>, <type>time</type>,
<type>timestamptz</type>, and <type>timestamp</type>. It stops on
the first matching format and emits the corresponding data type.
</para>
<para>
The <literal>datetime(<replaceable>template</replaceable>)</literal>
method determines the result type according to the fields used in the
provided template string.
</para>
<para>
The <literal>datetime()</literal> and
<literal>datetime(<replaceable>template</replaceable>)</literal> methods
use the same parsing rules as the <literal>to_timestamp</literal> SQL
function does (see <xref linkend="functions-formatting"/>), with three
exceptions. First, these methods don't allow unmatched template
patterns. Second, only the following separators are allowed in the
template string: minus sign, period, solidus (slash), comma, apostrophe,
semicolon, colon and space. Third, separators in the template string
must exactly match the input string.
</para>
<para>
If different date/time types need to be compared, an implicit cast is
applied. A <type>date</type> value can be cast to <type>timestamp</type>
or <type>timestamptz</type>, <type>timestamp</type> can be cast to
<type>timestamptz</type>, and <type>time</type> to <type>timetz</type>.
However, all but the first of these conversions depend on the current
<xref linkend="guc-timezone"/> setting, and thus can only be performed
within timezone-aware <type>jsonpath</type> functions.
</para>
</note>
<para>
<xref linkend="functions-sqljson-filter-ex-table"/> shows the available
filter expression elements.
</para>
<table id="functions-sqljson-filter-ex-table">
<title><type>jsonpath</type> Filter Expression Elements</title>
<tgroup cols="1">
<thead>
<row>
<entry role="func_table_entry"><para role="func_signature">
Predicate/Value
</para>
<para>
Description
</para>
<para>
Example(s)
</para></entry>
</row>
</thead>
<tbody>
<row>
<entry role="func_table_entry"><para role="func_signature">
<replaceable>value</replaceable> <literal>==</literal> <replaceable>value</replaceable>
<returnvalue>boolean</returnvalue>
</para>
<para>
Equality comparison (this, and the other comparison operators, work on
all JSON scalar values)
</para>
<para>
<literal>jsonb_path_query_array('[1, "a", 1, 3]', '$[*] ? (@ == 1)')</literal>
<returnvalue>[1, 1]</returnvalue>
</para>
<para>
<literal>jsonb_path_query_array('[1, "a", 1, 3]', '$[*] ? (@ == "a")')</literal>
<returnvalue>["a"]</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<replaceable>value</replaceable> <literal>!=</literal> <replaceable>value</replaceable>
<returnvalue>boolean</returnvalue>
</para>
<para role="func_signature">
<replaceable>value</replaceable> <literal><></literal> <replaceable>value</replaceable>
<returnvalue>boolean</returnvalue>
</para>
<para>
Non-equality comparison
</para>
<para>
<literal>jsonb_path_query_array('[1, 2, 1, 3]', '$[*] ? (@ != 1)')</literal>
<returnvalue>[2, 3]</returnvalue>
</para>
<para>
<literal>jsonb_path_query_array('["a", "b", "c"]', '$[*] ? (@ <> "b")')</literal>
<returnvalue>["a", "c"]</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<replaceable>value</replaceable> <literal><</literal> <replaceable>value</replaceable>
<returnvalue>boolean</returnvalue>
</para>
<para>
Less-than comparison
</para>
<para>
<literal>jsonb_path_query_array('[1, 2, 3]', '$[*] ? (@ < 2)')</literal>
<returnvalue>[1]</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<replaceable>value</replaceable> <literal><=</literal> <replaceable>value</replaceable>
<returnvalue>boolean</returnvalue>
</para>
<para>
Less-than-or-equal-to comparison
</para>
<para>
<literal>jsonb_path_query_array('["a", "b", "c"]', '$[*] ? (@ <= "b")')</literal>
<returnvalue>["a", "b"]</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<replaceable>value</replaceable> <literal>></literal> <replaceable>value</replaceable>
<returnvalue>boolean</returnvalue>
</para>
<para>
Greater-than comparison
</para>
<para>
<literal>jsonb_path_query_array('[1, 2, 3]', '$[*] ? (@ > 2)')</literal>
<returnvalue>[3]</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<replaceable>value</replaceable> <literal>>=</literal> <replaceable>value</replaceable>
<returnvalue>boolean</returnvalue>
</para>
<para>
Greater-than-or-equal-to comparison
</para>
<para>
<literal>jsonb_path_query_array('[1, 2, 3]', '$[*] ? (@ >= 2)')</literal>
<returnvalue>[2, 3]</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<literal>true</literal>
<returnvalue>boolean</returnvalue>
</para>
<para>
JSON constant <literal>true</literal>
</para>
<para>
<literal>jsonb_path_query('[{"name": "John", "parent": false}, {"name": "Chris", "parent": true}]', '$[*] ? (@.parent == true)')</literal>
<returnvalue>{"name": "Chris", "parent": true}</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<literal>false</literal>
<returnvalue>boolean</returnvalue>
</para>
<para>
JSON constant <literal>false</literal>
</para>
<para>
<literal>jsonb_path_query('[{"name": "John", "parent": false}, {"name": "Chris", "parent": true}]', '$[*] ? (@.parent == false)')</literal>
<returnvalue>{"name": "John", "parent": false}</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<literal>null</literal>
<returnvalue><replaceable>value</replaceable></returnvalue>
</para>
<para>
JSON constant <literal>null</literal> (note that, unlike in SQL,
comparison to <literal>null</literal> works normally)
</para>
<para>
<literal>jsonb_path_query('[{"name": "Mary", "job": null}, {"name": "Michael", "job": "driver"}]', '$[*] ? (@.job == null) .name')</literal>
<returnvalue>"Mary"</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<replaceable>boolean</replaceable> <literal>&&</literal> <replaceable>boolean</replaceable>
<returnvalue>boolean</returnvalue>
</para>
<para>
Boolean AND
</para>
<para>
<literal>jsonb_path_query('[1, 3, 7]', '$[*] ? (@ > 1 && @ < 5)')</literal>
<returnvalue>3</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<replaceable>boolean</replaceable> <literal>||</literal> <replaceable>boolean</replaceable>
<returnvalue>boolean</returnvalue>
</para>
<para>
Boolean OR
</para>
<para>
<literal>jsonb_path_query('[1, 3, 7]', '$[*] ? (@ < 1 || @ > 5)')</literal>
<returnvalue>7</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<literal>!</literal> <replaceable>boolean</replaceable>
<returnvalue>boolean</returnvalue>
</para>
<para>
Boolean NOT
</para>
<para>
<literal>jsonb_path_query('[1, 3, 7]', '$[*] ? (!(@ < 5))')</literal>
<returnvalue>7</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<replaceable>boolean</replaceable> <literal>is unknown</literal>
<returnvalue>boolean</returnvalue>
</para>
<para>
Tests whether a Boolean condition is <literal>unknown</literal>.
</para>
<para>
<literal>jsonb_path_query('[-1, 2, 7, "foo"]', '$[*] ? ((@ > 0) is unknown)')</literal>
<returnvalue>"foo"</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<replaceable>string</replaceable> <literal>like_regex</literal> <replaceable>string</replaceable> <optional> <literal>flag</literal> <replaceable>string</replaceable> </optional>
<returnvalue>boolean</returnvalue>
</para>
<para>
Tests whether the first operand matches the regular expression
given by the second operand, optionally with modifications
described by a string of <literal>flag</literal> characters (see
<xref linkend="jsonpath-regular-expressions"/>).
</para>
<para>
<literal>jsonb_path_query_array('["abc", "abd", "aBdC", "abdacb", "babc"]', '$[*] ? (@ like_regex "^ab.*c")')</literal>
<returnvalue>["abc", "abdacb"]</returnvalue>
</para>
<para>
<literal>jsonb_path_query_array('["abc", "abd", "aBdC", "abdacb", "babc"]', '$[*] ? (@ like_regex "^ab.*c" flag "i")')</literal>
<returnvalue>["abc", "aBdC", "abdacb"]</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<replaceable>string</replaceable> <literal>starts with</literal> <replaceable>string</replaceable>
<returnvalue>boolean</returnvalue>
</para>
<para>
Tests whether the second operand is an initial substring of the first
operand.
</para>
<para>
<literal>jsonb_path_query('["John Smith", "Mary Stone", "Bob Johnson"]', '$[*] ? (@ starts with "John")')</literal>
<returnvalue>"John Smith"</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<literal>exists</literal> <literal>(</literal> <replaceable>path_expression</replaceable> <literal>)</literal>
<returnvalue>boolean</returnvalue>
</para>
<para>
Tests whether a path expression matches at least one SQL/JSON item.
Returns <literal>unknown</literal> if the path expression would result
in an error; the second example uses this to avoid a no-such-key error
in strict mode.
</para>
<para>
<literal>jsonb_path_query('{"x": [1, 2], "y": [2, 4]}', 'strict $.* ? (exists (@ ? (@[*] > 2)))')</literal>
<returnvalue>[2, 4]</returnvalue>
</para>
<para>
<literal>jsonb_path_query_array('{"value": 41}', 'strict $ ? (exists (@.name)) .name')</literal>
<returnvalue>[]</returnvalue>
</para></entry>
</row>
</tbody>
</tgroup>
</table>
</sect3>
<sect3 id="jsonpath-regular-expressions">
<title>SQL/JSON Regular Expressions</title>
<indexterm zone="jsonpath-regular-expressions">
<primary><literal>LIKE_REGEX</literal></primary>
<secondary>in SQL/JSON</secondary>
</indexterm>
<para>
SQL/JSON path expressions allow matching text to a regular expression
with the <literal>like_regex</literal> filter. For example, the
following SQL/JSON path query would case-insensitively match all
strings in an array that start with an English vowel:
<programlisting>
$[*] ? (@ like_regex "^[aeiou]" flag "i")
</programlisting>
</para>
<para>
The optional <literal>flag</literal> string may include one or more of
the characters
<literal>i</literal> for case-insensitive match,
<literal>m</literal> to allow <literal>^</literal>
and <literal>$</literal> to match at newlines,
<literal>s</literal> to allow <literal>.</literal> to match a newline,
and <literal>q</literal> to quote the whole pattern (reducing the
behavior to a simple substring match).
</para>
<para>
The SQL/JSON standard borrows its definition for regular expressions
from the <literal>LIKE_REGEX</literal> operator, which in turn uses the
XQuery standard. PostgreSQL does not currently support the
<literal>LIKE_REGEX</literal> operator. Therefore,
the <literal>like_regex</literal> filter is implemented using the
POSIX regular expression engine described in
<xref linkend="functions-posix-regexp"/>. This leads to various minor
discrepancies from standard SQL/JSON behavior, which are cataloged in
<xref linkend="posix-vs-xquery"/>.
Note, however, that the flag-letter incompatibilities described there
do not apply to SQL/JSON, as it translates the XQuery flag letters to
match what the POSIX engine expects.
</para>
<para>
Keep in mind that the pattern argument of <literal>like_regex</literal>
is a JSON path string literal, written according to the rules given in
<xref linkend="datatype-jsonpath"/>. This means in particular that any
backslashes you want to use in the regular expression must be doubled.
For example, to match string values of the root document that contain
only digits:
<programlisting>
$.* ? (@ like_regex "^\\d+$")
</programlisting>
</para>
</sect3>
</sect2>
</sect1>
<sect1 id="functions-sequence">
<title>Sequence Manipulation Functions</title>
<indexterm>
<primary>sequence</primary>
</indexterm>
<para>
This section describes functions for operating on <firstterm>sequence
objects</firstterm>, also called sequence generators or just sequences.
Sequence objects are special single-row tables created with <xref
linkend="sql-createsequence"/>.
Sequence objects are commonly used to generate unique identifiers
for rows of a table. The sequence functions, listed in <xref
linkend="functions-sequence-table"/>, provide simple, multiuser-safe
methods for obtaining successive sequence values from sequence
objects.
</para>
<table id="functions-sequence-table">
<title>Sequence Functions</title>
<tgroup cols="1">
<thead>
<row>
<entry role="func_table_entry"><para role="func_signature">
Function
</para>
<para>
Description
</para></entry>
</row>
</thead>
<tbody>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>nextval</primary>
</indexterm>
<function>nextval</function> ( <type>regclass</type> )
<returnvalue>bigint</returnvalue>
</para>
<para>
Advances the sequence object to its next value and returns that value.
This is done atomically: even if multiple sessions
execute <function>nextval</function> concurrently, each will safely
receive a distinct sequence value.
If the sequence object has been created with default parameters,
successive <function>nextval</function> calls will return successive
values beginning with 1. Other behaviors can be obtained by using
appropriate parameters in the <xref linkend="sql-createsequence"/>
command.
</para>
<para>
This function requires <literal>USAGE</literal>
or <literal>UPDATE</literal> privilege on the sequence.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>setval</primary>
</indexterm>
<function>setval</function> ( <type>regclass</type>, <type>bigint</type> <optional>, <type>boolean</type> </optional> )
<returnvalue>bigint</returnvalue>
</para>
<para>
Sets the sequence object's current value, and optionally
its <literal>is_called</literal> flag. The two-parameter
form sets the sequence's <literal>last_value</literal> field to the
specified value and sets its <literal>is_called</literal> field to
<literal>true</literal>, meaning that the next
<function>nextval</function> will advance the sequence before
returning a value. The value that will be reported
by <function>currval</function> is also set to the specified value.
In the three-parameter form, <literal>is_called</literal> can be set
to either <literal>true</literal>
or <literal>false</literal>. <literal>true</literal> has the same
effect as the two-parameter form. If it is set
to <literal>false</literal>, the next <function>nextval</function>
will return exactly the specified value, and sequence advancement
commences with the following <function>nextval</function>.
Furthermore, the value reported by <function>currval</function> is not
changed in this case. For example,
<programlisting>
SELECT setval('myseq', 42); <lineannotation>Next <function>nextval</function> will return 43</lineannotation>
SELECT setval('myseq', 42, true); <lineannotation>Same as above</lineannotation>
SELECT setval('myseq', 42, false); <lineannotation>Next <function>nextval</function> will return 42</lineannotation>
</programlisting>
The result returned by <function>setval</function> is just the value of its
second argument.
</para>
<para>
This function requires <literal>UPDATE</literal> privilege on the
sequence.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>currval</primary>
</indexterm>
<function>currval</function> ( <type>regclass</type> )
<returnvalue>bigint</returnvalue>
</para>
<para>
Returns the value most recently obtained
by <function>nextval</function> for this sequence in the current
session. (An error is reported if <function>nextval</function> has
never been called for this sequence in this session.) Because this is
returning a session-local value, it gives a predictable answer whether
or not other sessions have executed <function>nextval</function> since
the current session did.
</para>
<para>
This function requires <literal>USAGE</literal>
or <literal>SELECT</literal> privilege on the sequence.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>lastval</primary>
</indexterm>
<function>lastval</function> ()
<returnvalue>bigint</returnvalue>
</para>
<para>
Returns the value most recently returned by
<function>nextval</function> in the current session. This function is
identical to <function>currval</function>, except that instead
of taking the sequence name as an argument it refers to whichever
sequence <function>nextval</function> was most recently applied to
in the current session. It is an error to call
<function>lastval</function> if <function>nextval</function>
has not yet been called in the current session.
</para>
<para>
This function requires <literal>USAGE</literal>
or <literal>SELECT</literal> privilege on the last used sequence.
</para></entry>
</row>
</tbody>
</tgroup>
</table>
<caution>
<para>
To avoid blocking concurrent transactions that obtain numbers from
the same sequence, a <function>nextval</function> operation is never
rolled back; that is, once a value has been fetched it is considered
used and will not be returned again. This is true even if the
surrounding transaction later aborts, or if the calling query ends
up not using the value. For example an <command>INSERT</command> with
an <literal>ON CONFLICT</literal> clause will compute the to-be-inserted
tuple, including doing any required <function>nextval</function>
calls, before detecting any conflict that would cause it to follow
the <literal>ON CONFLICT</literal> rule instead. Such cases will leave
unused <quote>holes</quote> in the sequence of assigned values.
Thus, <productname>PostgreSQL</productname> sequence
objects <emphasis>cannot be used to obtain <quote>gapless</quote>
sequences</emphasis>.
</para>
<para>
Likewise, any sequence state changes made by <function>setval</function>
are not undone if the transaction rolls back.
</para>
</caution>
<para>
The sequence to be operated on by a sequence function is specified by
a <type>regclass</type> argument, which is simply the OID of the sequence in the
<structname>pg_class</structname> system catalog. You do not have to look up the
OID by hand, however, since the <type>regclass</type> data type's input
converter will do the work for you. See <xref linkend="datatype-oid"/>
for details.
</para>
</sect1>
<sect1 id="functions-conditional">
<title>Conditional Expressions</title>
<indexterm>
<primary>CASE</primary>
</indexterm>
<indexterm>
<primary>conditional expression</primary>
</indexterm>
<para>
This section describes the <acronym>SQL</acronym>-compliant conditional expressions
available in <productname>PostgreSQL</productname>.
</para>
<tip>
<para>
If your needs go beyond the capabilities of these conditional
expressions, you might want to consider writing a server-side function
in a more expressive programming language.
</para>
</tip>
<note>
<para>
Although <token>COALESCE</token>, <token>GREATEST</token>, and
<token>LEAST</token> are syntactically similar to functions, they are
not ordinary functions, and thus cannot be used with explicit
<token>VARIADIC</token> array arguments.
</para>
</note>
<sect2 id="functions-case">
<title><literal>CASE</literal></title>
<para>
The <acronym>SQL</acronym> <token>CASE</token> expression is a
generic conditional expression, similar to if/else statements in
other programming languages:
<synopsis>
CASE WHEN <replaceable>condition</replaceable> THEN <replaceable>result</replaceable>
<optional>WHEN ...</optional>
<optional>ELSE <replaceable>result</replaceable></optional>
END
</synopsis>
<token>CASE</token> clauses can be used wherever
an expression is valid. Each <replaceable>condition</replaceable> is an
expression that returns a <type>boolean</type> result. If the condition's
result is true, the value of the <token>CASE</token> expression is the
<replaceable>result</replaceable> that follows the condition, and the
remainder of the <token>CASE</token> expression is not processed. If the
condition's result is not true, any subsequent <token>WHEN</token> clauses
are examined in the same manner. If no <token>WHEN</token>
<replaceable>condition</replaceable> yields true, the value of the
<token>CASE</token> expression is the <replaceable>result</replaceable> of the
<token>ELSE</token> clause. If the <token>ELSE</token> clause is
omitted and no condition is true, the result is null.
</para>
<para>
An example:
<screen>
SELECT * FROM test;
a
---
1
2
3
SELECT a,
CASE WHEN a=1 THEN 'one'
WHEN a=2 THEN 'two'
ELSE 'other'
END
FROM test;
a | case
---+-------
1 | one
2 | two
3 | other
</screen>
</para>
<para>
The data types of all the <replaceable>result</replaceable>
expressions must be convertible to a single output type.
See <xref linkend="typeconv-union-case"/> for more details.
</para>
<para>
There is a <quote>simple</quote> form of <token>CASE</token> expression
that is a variant of the general form above:
<synopsis>
CASE <replaceable>expression</replaceable>
WHEN <replaceable>value</replaceable> THEN <replaceable>result</replaceable>
<optional>WHEN ...</optional>
<optional>ELSE <replaceable>result</replaceable></optional>
END
</synopsis>
The first
<replaceable>expression</replaceable> is computed, then compared to
each of the <replaceable>value</replaceable> expressions in the
<token>WHEN</token> clauses until one is found that is equal to it. If
no match is found, the <replaceable>result</replaceable> of the
<token>ELSE</token> clause (or a null value) is returned. This is similar
to the <function>switch</function> statement in C.
</para>
<para>
The example above can be written using the simple
<token>CASE</token> syntax:
<screen>
SELECT a,
CASE a WHEN 1 THEN 'one'
WHEN 2 THEN 'two'
ELSE 'other'
END
FROM test;
a | case
---+-------
1 | one
2 | two
3 | other
</screen>
</para>
<para>
A <token>CASE</token> expression does not evaluate any subexpressions
that are not needed to determine the result. For example, this is a
possible way of avoiding a division-by-zero failure:
<programlisting>
SELECT ... WHERE CASE WHEN x <> 0 THEN y/x > 1.5 ELSE false END;
</programlisting>
</para>
<note>
<para>
As described in <xref linkend="syntax-express-eval"/>, there are various
situations in which subexpressions of an expression are evaluated at
different times, so that the principle that <quote><token>CASE</token>
evaluates only necessary subexpressions</quote> is not ironclad. For
example a constant <literal>1/0</literal> subexpression will usually result in
a division-by-zero failure at planning time, even if it's within
a <token>CASE</token> arm that would never be entered at run time.
</para>
</note>
</sect2>
<sect2 id="functions-coalesce-nvl-ifnull">
<title><literal>COALESCE</literal></title>
<indexterm>
<primary>COALESCE</primary>
</indexterm>
<indexterm>
<primary>NVL</primary>
</indexterm>
<indexterm>
<primary>IFNULL</primary>
</indexterm>
<synopsis>
<function>COALESCE</function>(<replaceable>value</replaceable> <optional>, ...</optional>)
</synopsis>
<para>
The <function>COALESCE</function> function returns the first of its
arguments that is not null. Null is returned only if all arguments
are null. It is often used to substitute a default value for
null values when data is retrieved for display, for example:
<programlisting>
SELECT COALESCE(description, short_description, '(none)') ...
</programlisting>
This returns <varname>description</varname> if it is not null, otherwise
<varname>short_description</varname> if it is not null, otherwise <literal>(none)</literal>.
</para>
<para>
The arguments must all be convertible to a common data type, which
will be the type of the result (see
<xref linkend="typeconv-union-case"/> for details).
</para>
<para>
Like a <token>CASE</token> expression, <function>COALESCE</function> only
evaluates the arguments that are needed to determine the result;
that is, arguments to the right of the first non-null argument are
not evaluated. This SQL-standard function provides capabilities similar
to <function>NVL</function> and <function>IFNULL</function>, which are used in some other
database systems.
</para>
</sect2>
<sect2 id="functions-nullif">
<title><literal>NULLIF</literal></title>
<indexterm>
<primary>NULLIF</primary>
</indexterm>
<synopsis>
<function>NULLIF</function>(<replaceable>value1</replaceable>, <replaceable>value2</replaceable>)
</synopsis>
<para>
The <function>NULLIF</function> function returns a null value if
<replaceable>value1</replaceable> equals <replaceable>value2</replaceable>;
otherwise it returns <replaceable>value1</replaceable>.
This can be used to perform the inverse operation of the
<function>COALESCE</function> example given above:
<programlisting>
SELECT NULLIF(value, '(none)') ...
</programlisting>
In this example, if <literal>value</literal> is <literal>(none)</literal>,
null is returned, otherwise the value of <literal>value</literal>
is returned.
</para>
<para>
The two arguments must be of comparable types.
To be specific, they are compared exactly as if you had
written <literal><replaceable>value1</replaceable>
= <replaceable>value2</replaceable></literal>, so there must be a
suitable <literal>=</literal> operator available.
</para>
<para>
The result has the same type as the first argument — but there is
a subtlety. What is actually returned is the first argument of the
implied <literal>=</literal> operator, and in some cases that will have
been promoted to match the second argument's type. For
example, <literal>NULLIF(1, 2.2)</literal> yields <type>numeric</type>,
because there is no <type>integer</type> <literal>=</literal>
<type>numeric</type> operator,
only <type>numeric</type> <literal>=</literal> <type>numeric</type>.
</para>
</sect2>
<sect2 id="functions-greatest-least">
<title><literal>GREATEST</literal> and <literal>LEAST</literal></title>
<indexterm>
<primary>GREATEST</primary>
</indexterm>
<indexterm>
<primary>LEAST</primary>
</indexterm>
<synopsis>
<function>GREATEST</function>(<replaceable>value</replaceable> <optional>, ...</optional>)
</synopsis>
<synopsis>
<function>LEAST</function>(<replaceable>value</replaceable> <optional>, ...</optional>)
</synopsis>
<para>
The <function>GREATEST</function> and <function>LEAST</function> functions select the
largest or smallest value from a list of any number of expressions.
The expressions must all be convertible to a common data type, which
will be the type of the result
(see <xref linkend="typeconv-union-case"/> for details). NULL values
in the list are ignored. The result will be NULL only if all the
expressions evaluate to NULL.
</para>
<para>
Note that <function>GREATEST</function> and <function>LEAST</function> are not in
the SQL standard, but are a common extension. Some other databases
make them return NULL if any argument is NULL, rather than only when
all are NULL.
</para>
</sect2>
</sect1>
<sect1 id="functions-array">
<title>Array Functions and Operators</title>
<para>
<xref linkend="array-operators-table"/> shows the specialized operators
available for array types.
In addition to those, the usual comparison operators shown in <xref
linkend="functions-comparison-op-table"/> are available for
arrays. The comparison operators compare the array contents
element-by-element, using the default B-tree comparison function for
the element data type, and sort based on the first difference.
In multidimensional arrays the elements are visited in row-major order
(last subscript varies most rapidly).
If the contents of two arrays are equal but the dimensionality is
different, the first difference in the dimensionality information
determines the sort order.
</para>
<table id="array-operators-table">
<title>Array Operators</title>
<tgroup cols="1">
<thead>
<row>
<entry role="func_table_entry"><para role="func_signature">
Operator
</para>
<para>
Description
</para>
<para>
Example(s)
</para></entry>
</row>
</thead>
<tbody>
<row>
<entry role="func_table_entry"><para role="func_signature">
<type>anyarray</type> <literal>@></literal> <type>anyarray</type>
<returnvalue>boolean</returnvalue>
</para>
<para>
Does the first array contain the second, that is, does each element
appearing in the second array equal some element of the first array?
(Duplicates are not treated specially,
thus <literal>ARRAY[1]</literal> and <literal>ARRAY[1,1]</literal> are
each considered to contain the other.)
</para>
<para>
<literal>ARRAY[1,4,3] @> ARRAY[3,1,3]</literal>
<returnvalue>t</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<type>anyarray</type> <literal><@</literal> <type>anyarray</type>
<returnvalue>boolean</returnvalue>
</para>
<para>
Is the first array contained by the second?
</para>
<para>
<literal>ARRAY[2,2,7] <@ ARRAY[1,7,4,2,6]</literal>
<returnvalue>t</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<type>anyarray</type> <literal>&&</literal> <type>anyarray</type>
<returnvalue>boolean</returnvalue>
</para>
<para>
Do the arrays overlap, that is, have any elements in common?
</para>
<para>
<literal>ARRAY[1,4,3] && ARRAY[2,1]</literal>
<returnvalue>t</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<type>anycompatiblearray</type> <literal>||</literal> <type>anycompatiblearray</type>
<returnvalue>anycompatiblearray</returnvalue>
</para>
<para>
Concatenates the two arrays. Concatenating a null or empty array is a
no-op; otherwise the arrays must have the same number of dimensions
(as illustrated by the first example) or differ in number of
dimensions by one (as illustrated by the second).
If the arrays are not of identical element types, they will be coerced
to a common type (see <xref linkend="typeconv-union-case"/>).
</para>
<para>
<literal>ARRAY[1,2,3] || ARRAY[4,5,6,7]</literal>
<returnvalue>{1,2,3,4,5,6,7}</returnvalue>
</para>
<para>
<literal>ARRAY[1,2,3] || ARRAY[[4,5,6],[7,8,9.9]]</literal>
<returnvalue>{{1,2,3},{4,5,6},{7,8,9.9}}</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<type>anycompatible</type> <literal>||</literal> <type>anycompatiblearray</type>
<returnvalue>anycompatiblearray</returnvalue>
</para>
<para>
Concatenates an element onto the front of an array (which must be
empty or one-dimensional).
</para>
<para>
<literal>3 || ARRAY[4,5,6]</literal>
<returnvalue>{3,4,5,6}</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<type>anycompatiblearray</type> <literal>||</literal> <type>anycompatible</type>
<returnvalue>anycompatiblearray</returnvalue>
</para>
<para>
Concatenates an element onto the end of an array (which must be
empty or one-dimensional).
</para>
<para>
<literal>ARRAY[4,5,6] || 7</literal>
<returnvalue>{4,5,6,7}</returnvalue>
</para></entry>
</row>
</tbody>
</tgroup>
</table>
<para>
See <xref linkend="arrays"/> for more details about array operator
behavior. See <xref linkend="indexes-types"/> for more details about
which operators support indexed operations.
</para>
<para>
<xref linkend="array-functions-table"/> shows the functions
available for use with array types. See <xref linkend="arrays"/>
for more information and examples of the use of these functions.
</para>
<table id="array-functions-table">
<title>Array Functions</title>
<tgroup cols="1">
<thead>
<row>
<entry role="func_table_entry"><para role="func_signature">
Function
</para>
<para>
Description
</para>
<para>
Example(s)
</para></entry>
</row>
</thead>
<tbody>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>array_append</primary>
</indexterm>
<function>array_append</function> ( <type>anycompatiblearray</type>, <type>anycompatible</type> )
<returnvalue>anycompatiblearray</returnvalue>
</para>
<para>
Appends an element to the end of an array (same as
the <type>anycompatiblearray</type> <literal>||</literal> <type>anycompatible</type>
operator).
</para>
<para>
<literal>array_append(ARRAY[1,2], 3)</literal>
<returnvalue>{1,2,3}</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>array_cat</primary>
</indexterm>
<function>array_cat</function> ( <type>anycompatiblearray</type>, <type>anycompatiblearray</type> )
<returnvalue>anycompatiblearray</returnvalue>
</para>
<para>
Concatenates two arrays (same as
the <type>anycompatiblearray</type> <literal>||</literal> <type>anycompatiblearray</type>
operator).
</para>
<para>
<literal>array_cat(ARRAY[1,2,3], ARRAY[4,5])</literal>
<returnvalue>{1,2,3,4,5}</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>array_dims</primary>
</indexterm>
<function>array_dims</function> ( <type>anyarray</type> )
<returnvalue>text</returnvalue>
</para>
<para>
Returns a text representation of the array's dimensions.
</para>
<para>
<literal>array_dims(ARRAY[[1,2,3], [4,5,6]])</literal>
<returnvalue>[1:2][1:3]</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>array_fill</primary>
</indexterm>
<function>array_fill</function> ( <type>anyelement</type>, <type>integer[]</type>
<optional>, <type>integer[]</type> </optional> )
<returnvalue>anyarray</returnvalue>
</para>
<para>
Returns an array filled with copies of the given value, having
dimensions of the lengths specified by the second argument.
The optional third argument supplies lower-bound values for each
dimension (which default to all <literal>1</literal>).
</para>
<para>
<literal>array_fill(11, ARRAY[2,3])</literal>
<returnvalue>{{11,11,11},{11,11,11}}</returnvalue>
</para>
<para>
<literal>array_fill(7, ARRAY[3], ARRAY[2])</literal>
<returnvalue>[2:4]={7,7,7}</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>array_length</primary>
</indexterm>
<function>array_length</function> ( <type>anyarray</type>, <type>integer</type> )
<returnvalue>integer</returnvalue>
</para>
<para>
Returns the length of the requested array dimension.
</para>
<para>
<literal>array_length(array[1,2,3], 1)</literal>
<returnvalue>3</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>array_lower</primary>
</indexterm>
<function>array_lower</function> ( <type>anyarray</type>, <type>integer</type> )
<returnvalue>integer</returnvalue>
</para>
<para>
Returns the lower bound of the requested array dimension.
</para>
<para>
<literal>array_lower('[0:2]={1,2,3}'::integer[], 1)</literal>
<returnvalue>0</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>array_ndims</primary>
</indexterm>
<function>array_ndims</function> ( <type>anyarray</type> )
<returnvalue>integer</returnvalue>
</para>
<para>
Returns the number of dimensions of the array.
</para>
<para>
<literal>array_ndims(ARRAY[[1,2,3], [4,5,6]])</literal>
<returnvalue>2</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>array_position</primary>
</indexterm>
<function>array_position</function> ( <type>anycompatiblearray</type>, <type>anycompatible</type> <optional>, <type>integer</type> </optional> )
<returnvalue>integer</returnvalue>
</para>
<para>
Returns the subscript of the first occurrence of the second argument
in the array, or <literal>NULL</literal> if it's not present.
If the third argument is given, the search begins at that subscript.
The array must be one-dimensional.
Comparisons are done using <literal>IS NOT DISTINCT FROM</literal>
semantics, so it is possible to search for <literal>NULL</literal>.
</para>
<para>
<literal>array_position(ARRAY['sun', 'mon', 'tue', 'wed', 'thu', 'fri', 'sat'], 'mon')</literal>
<returnvalue>2</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>array_positions</primary>
</indexterm>
<function>array_positions</function> ( <type>anycompatiblearray</type>, <type>anycompatible</type> )
<returnvalue>integer[]</returnvalue>
</para>
<para>
Returns an array of the subscripts of all occurrences of the second
argument in the array given as first argument.
The array must be one-dimensional.
Comparisons are done using <literal>IS NOT DISTINCT FROM</literal>
semantics, so it is possible to search for <literal>NULL</literal>.
<literal>NULL</literal> is returned only if the array
is <literal>NULL</literal>; if the value is not found in the array, an
empty array is returned.
</para>
<para>
<literal>array_positions(ARRAY['A','A','B','A'], 'A')</literal>
<returnvalue>{1,2,4}</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>array_prepend</primary>
</indexterm>
<function>array_prepend</function> ( <type>anycompatible</type>, <type>anycompatiblearray</type> )
<returnvalue>anycompatiblearray</returnvalue>
</para>
<para>
Prepends an element to the beginning of an array (same as
the <type>anycompatible</type> <literal>||</literal> <type>anycompatiblearray</type>
operator).
</para>
<para>
<literal>array_prepend(1, ARRAY[2,3])</literal>
<returnvalue>{1,2,3}</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>array_remove</primary>
</indexterm>
<function>array_remove</function> ( <type>anycompatiblearray</type>, <type>anycompatible</type> )
<returnvalue>anycompatiblearray</returnvalue>
</para>
<para>
Removes all elements equal to the given value from the array.
The array must be one-dimensional.
Comparisons are done using <literal>IS NOT DISTINCT FROM</literal>
semantics, so it is possible to remove <literal>NULL</literal>s.
</para>
<para>
<literal>array_remove(ARRAY[1,2,3,2], 2)</literal>
<returnvalue>{1,3}</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>array_replace</primary>
</indexterm>
<function>array_replace</function> ( <type>anycompatiblearray</type>, <type>anycompatible</type>, <type>anycompatible</type> )
<returnvalue>anycompatiblearray</returnvalue>
</para>
<para>
Replaces each array element equal to the second argument with the
third argument.
</para>
<para>
<literal>array_replace(ARRAY[1,2,5,4], 5, 3)</literal>
<returnvalue>{1,2,3,4}</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>array_to_string</primary>
</indexterm>
<function>array_to_string</function> ( <parameter>array</parameter> <type>anyarray</type>, <parameter>delimiter</parameter> <type>text</type> <optional>, <parameter>null_string</parameter> <type>text</type> </optional> )
<returnvalue>text</returnvalue>
</para>
<para>
Converts each array element to its text representation, and
concatenates those separated by
the <parameter>delimiter</parameter> string.
If <parameter>null_string</parameter> is given and is
not <literal>NULL</literal>, then <literal>NULL</literal> array
entries are represented by that string; otherwise, they are omitted.
</para>
<para>
<literal>array_to_string(ARRAY[1, 2, 3, NULL, 5], ',', '*')</literal>
<returnvalue>1,2,3,*,5</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>array_upper</primary>
</indexterm>
<function>array_upper</function> ( <type>anyarray</type>, <type>integer</type> )
<returnvalue>integer</returnvalue>
</para>
<para>
Returns the upper bound of the requested array dimension.
</para>
<para>
<literal>array_upper(ARRAY[1,8,3,7], 1)</literal>
<returnvalue>4</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>cardinality</primary>
</indexterm>
<function>cardinality</function> ( <type>anyarray</type> )
<returnvalue>integer</returnvalue>
</para>
<para>
Returns the total number of elements in the array, or 0 if the array
is empty.
</para>
<para>
<literal>cardinality(ARRAY[[1,2],[3,4]])</literal>
<returnvalue>4</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>trim_array</primary>
</indexterm>
<function>trim_array</function> ( <parameter>array</parameter> <type>anyarray</type>, <parameter>n</parameter> <type>integer</type> )
<returnvalue>anyarray</returnvalue>
</para>
<para>
Trims an array by removing the last <parameter>n</parameter> elements.
If the array is multidimensional, only the first dimension is trimmed.
</para>
<para>
<literal>trim_array(ARRAY[1,2,3,4,5,6], 2)</literal>
<returnvalue>{1,2,3,4}</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>unnest</primary>
</indexterm>
<function>unnest</function> ( <type>anyarray</type> )
<returnvalue>setof anyelement</returnvalue>
</para>
<para>
Expands an array into a set of rows.
The array's elements are read out in storage order.
</para>
<para>
<literal>unnest(ARRAY[1,2])</literal>
<returnvalue></returnvalue>
<programlisting>
1
2
</programlisting>
</para>
<para>
<literal>unnest(ARRAY[['foo','bar'],['baz','quux']])</literal>
<returnvalue></returnvalue>
<programlisting>
foo
bar
baz
quux
</programlisting>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<function>unnest</function> ( <type>anyarray</type>, <type>anyarray</type> <optional>, ... </optional> )
<returnvalue>setof anyelement, anyelement [, ... ]</returnvalue>
</para>
<para>
Expands multiple arrays (possibly of different data types) into a set of
rows. If the arrays are not all the same length then the shorter ones
are padded with <literal>NULL</literal>s. This form is only allowed
in a query's FROM clause; see <xref linkend="queries-tablefunctions"/>.
</para>
<para>
<literal>select * from unnest(ARRAY[1,2], ARRAY['foo','bar','baz']) as x(a,b)</literal>
<returnvalue></returnvalue>
<programlisting>
a | b
---+-----
1 | foo
2 | bar
| baz
</programlisting>
</para></entry>
</row>
</tbody>
</tgroup>
</table>
<note>
<para>
There are two differences in the behavior of <function>string_to_array</function>
from pre-9.1 versions of <productname>PostgreSQL</productname>.
First, it will return an empty (zero-element) array rather
than <literal>NULL</literal> when the input string is of zero length.
Second, if the delimiter string is <literal>NULL</literal>, the function
splits the input into individual characters, rather than
returning <literal>NULL</literal> as before.
</para>
</note>
<para>
See also <xref linkend="functions-aggregate"/> about the aggregate
function <function>array_agg</function> for use with arrays.
</para>
</sect1>
<sect1 id="functions-range">
<title>Range/Multirange Functions and Operators</title>
<para>
See <xref linkend="rangetypes"/> for an overview of range types.
</para>
<para>
<xref linkend="range-operators-table"/> shows the specialized operators
available for range types.
<xref linkend="multirange-operators-table"/> shows the specialized operators
available for multirange types.
In addition to those, the usual comparison operators shown in
<xref linkend="functions-comparison-op-table"/> are available for range
and multirange types. The comparison operators order first by the range lower
bounds, and only if those are equal do they compare the upper bounds. The
multirange operators compare each range until one is unequal. This
does not usually result in a useful overall ordering, but the operators are
provided to allow unique indexes to be constructed on ranges.
</para>
<table id="range-operators-table">
<title>Range Operators</title>
<tgroup cols="1">
<thead>
<row>
<entry role="func_table_entry"><para role="func_signature">
Operator
</para>
<para>
Description
</para>
<para>
Example(s)
</para></entry>
</row>
</thead>
<tbody>
<row>
<entry role="func_table_entry"><para role="func_signature">
<type>anyrange</type> <literal>@></literal> <type>anyrange</type>
<returnvalue>boolean</returnvalue>
</para>
<para>
Does the first range contain the second?
</para>
<para>
<literal>int4range(2,4) @> int4range(2,3)</literal>
<returnvalue>t</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<type>anyrange</type> <literal>@></literal> <type>anyelement</type>
<returnvalue>boolean</returnvalue>
</para>
<para>
Does the range contain the element?
</para>
<para>
<literal>'[2011-01-01,2011-03-01)'::tsrange @> '2011-01-10'::timestamp</literal>
<returnvalue>t</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<type>anyrange</type> <literal><@</literal> <type>anyrange</type>
<returnvalue>boolean</returnvalue>
</para>
<para>
Is the first range contained by the second?
</para>
<para>
<literal>int4range(2,4) <@ int4range(1,7)</literal>
<returnvalue>t</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<type>anyelement</type> <literal><@</literal> <type>anyrange</type>
<returnvalue>boolean</returnvalue>
</para>
<para>
Is the element contained in the range?
</para>
<para>
<literal>42 <@ int4range(1,7)</literal>
<returnvalue>f</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<type>anyrange</type> <literal>&&</literal> <type>anyrange</type>
<returnvalue>boolean</returnvalue>
</para>
<para>
Do the ranges overlap, that is, have any elements in common?
</para>
<para>
<literal>int8range(3,7) && int8range(4,12)</literal>
<returnvalue>t</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<type>anyrange</type> <literal><<</literal> <type>anyrange</type>
<returnvalue>boolean</returnvalue>
</para>
<para>
Is the first range strictly left of the second?
</para>
<para>
<literal>int8range(1,10) << int8range(100,110)</literal>
<returnvalue>t</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<type>anyrange</type> <literal>>></literal> <type>anyrange</type>
<returnvalue>boolean</returnvalue>
</para>
<para>
Is the first range strictly right of the second?
</para>
<para>
<literal>int8range(50,60) >> int8range(20,30)</literal>
<returnvalue>t</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<type>anyrange</type> <literal>&<</literal> <type>anyrange</type>
<returnvalue>boolean</returnvalue>
</para>
<para>
Does the first range not extend to the right of the second?
</para>
<para>
<literal>int8range(1,20) &< int8range(18,20)</literal>
<returnvalue>t</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<type>anyrange</type> <literal>&></literal> <type>anyrange</type>
<returnvalue>boolean</returnvalue>
</para>
<para>
Does the first range not extend to the left of the second?
</para>
<para>
<literal>int8range(7,20) &> int8range(5,10)</literal>
<returnvalue>t</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<type>anyrange</type> <literal>-|-</literal> <type>anyrange</type>
<returnvalue>boolean</returnvalue>
</para>
<para>
Are the ranges adjacent?
</para>
<para>
<literal>numrange(1.1,2.2) -|- numrange(2.2,3.3)</literal>
<returnvalue>t</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<type>anyrange</type> <literal>+</literal> <type>anyrange</type>
<returnvalue>anyrange</returnvalue>
</para>
<para>
Computes the union of the ranges. The ranges must overlap or be
adjacent, so that the union is a single range (but
see <function>range_merge()</function>).
</para>
<para>
<literal>numrange(5,15) + numrange(10,20)</literal>
<returnvalue>[5,20)</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<type>anyrange</type> <literal>*</literal> <type>anyrange</type>
<returnvalue>anyrange</returnvalue>
</para>
<para>
Computes the intersection of the ranges.
</para>
<para>
<literal>int8range(5,15) * int8range(10,20)</literal>
<returnvalue>[10,15)</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<type>anyrange</type> <literal>-</literal> <type>anyrange</type>
<returnvalue>anyrange</returnvalue>
</para>
<para>
Computes the difference of the ranges. The second range must not be
contained in the first in such a way that the difference would not be
a single range.
</para>
<para>
<literal>int8range(5,15) - int8range(10,20)</literal>
<returnvalue>[5,10)</returnvalue>
</para></entry>
</row>
</tbody>
</tgroup>
</table>
<table id="multirange-operators-table">
<title>Multirange Operators</title>
<tgroup cols="1">
<thead>
<row>
<entry role="func_table_entry"><para role="func_signature">
Operator
</para>
<para>
Description
</para>
<para>
Example(s)
</para></entry>
</row>
</thead>
<tbody>
<row>
<entry role="func_table_entry"><para role="func_signature">
<type>anymultirange</type> <literal>@></literal> <type>anymultirange</type>
<returnvalue>boolean</returnvalue>
</para>
<para>
Does the first multirange contain the second?
</para>
<para>
<literal>'{[2,4)}'::int4multirange @> '{[2,3)}'::int4multirange</literal>
<returnvalue>t</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<type>anymultirange</type> <literal>@></literal> <type>anyrange</type>
<returnvalue>boolean</returnvalue>
</para>
<para>
Does the multirange contain the range?
</para>
<para>
<literal>'{[2,4)}'::int4multirange @> int4range(2,3)</literal>
<returnvalue>t</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<type>anymultirange</type> <literal>@></literal> <type>anyelement</type>
<returnvalue>boolean</returnvalue>
</para>
<para>
Does the multirange contain the element?
</para>
<para>
<literal>'{[2011-01-01,2011-03-01)}'::tsmultirange @> '2011-01-10'::timestamp</literal>
<returnvalue>t</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<type>anyrange</type> <literal>@></literal> <type>anymultirange</type>
<returnvalue>boolean</returnvalue>
</para>
<para>
Does the range contain the multirange?
</para>
<para>
<literal>'[2,4)'::int4range @> '{[2,3)}'::int4multirange</literal>
<returnvalue>t</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<type>anymultirange</type> <literal><@</literal> <type>anymultirange</type>
<returnvalue>boolean</returnvalue>
</para>
<para>
Is the first multirange contained by the second?
</para>
<para>
<literal>'{[2,4)}'::int4multirange <@ '{[1,7)}'::int4multirange</literal>
<returnvalue>t</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<type>anymultirange</type> <literal><@</literal> <type>anyrange</type>
<returnvalue>boolean</returnvalue>
</para>
<para>
Is the multirange contained by the range?
</para>
<para>
<literal>'{[2,4)}'::int4multirange <@ int4range(1,7)</literal>
<returnvalue>t</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<type>anyrange</type> <literal><@</literal> <type>anymultirange</type>
<returnvalue>boolean</returnvalue>
</para>
<para>
Is the range contained by the multirange?
</para>
<para>
<literal>int4range(2,4) <@ '{[1,7)}'::int4multirange</literal>
<returnvalue>t</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<type>anyelement</type> <literal><@</literal> <type>anymultirange</type>
<returnvalue>boolean</returnvalue>
</para>
<para>
Is the element contained by the multirange?
</para>
<para>
<literal>42 <@ '{[1,7)}'::int4multirange</literal>
<returnvalue>t</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<type>anymultirange</type> <literal>&&</literal> <type>anymultirange</type>
<returnvalue>boolean</returnvalue>
</para>
<para>
Do the multiranges overlap, that is, have any elements in common?
</para>
<para>
<literal>'{[3,7)}'::int8multirange && '{[4,12)}'::int8multirange</literal>
<returnvalue>t</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<type>anymultirange</type> <literal>&&</literal> <type>anyrange</type>
<returnvalue>boolean</returnvalue>
</para>
<para>
Does the multirange overlap the range?
</para>
<para>
<literal>'{[3,7)}'::int8multirange && int8range(4,12)</literal>
<returnvalue>t</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<type>anyrange</type> <literal>&&</literal> <type>anymultirange</type>
<returnvalue>boolean</returnvalue>
</para>
<para>
Does the range overlap the multirange?
</para>
<para>
<literal>int8range(3,7) && '{[4,12)}'::int8multirange</literal>
<returnvalue>t</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<type>anymultirange</type> <literal><<</literal> <type>anymultirange</type>
<returnvalue>boolean</returnvalue>
</para>
<para>
Is the first multirange strictly left of the second?
</para>
<para>
<literal>'{[1,10)}'::int8multirange << '{[100,110)}'::int8multirange</literal>
<returnvalue>t</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<type>anymultirange</type> <literal><<</literal> <type>anyrange</type>
<returnvalue>boolean</returnvalue>
</para>
<para>
Is the multirange strictly left of the range?
</para>
<para>
<literal>'{[1,10)}'::int8multirange << int8range(100,110)</literal>
<returnvalue>t</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<type>anyrange</type> <literal><<</literal> <type>anymultirange</type>
<returnvalue>boolean</returnvalue>
</para>
<para>
Is the range strictly left of the multirange?
</para>
<para>
<literal>int8range(1,10) << '{[100,110)}'::int8multirange</literal>
<returnvalue>t</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<type>anymultirange</type> <literal>>></literal> <type>anymultirange</type>
<returnvalue>boolean</returnvalue>
</para>
<para>
Is the first multirange strictly right of the second?
</para>
<para>
<literal>'{[50,60)}'::int8multirange >> '{[20,30)}'::int8multirange</literal>
<returnvalue>t</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<type>anymultirange</type> <literal>>></literal> <type>anyrange</type>
<returnvalue>boolean</returnvalue>
</para>
<para>
Is the multirange strictly right of the range?
</para>
<para>
<literal>'{[50,60)}'::int8multirange >> int8range(20,30)</literal>
<returnvalue>t</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<type>anyrange</type> <literal>>></literal> <type>anymultirange</type>
<returnvalue>boolean</returnvalue>
</para>
<para>
Is the range strictly right of the multirange?
</para>
<para>
<literal>int8range(50,60) >> '{[20,30)}'::int8multirange</literal>
<returnvalue>t</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<type>anymultirange</type> <literal>&<</literal> <type>anymultirange</type>
<returnvalue>boolean</returnvalue>
</para>
<para>
Does the first multirange not extend to the right of the second?
</para>
<para>
<literal>'{[1,20)}'::int8multirange &< '{[18,20)}'::int8multirange</literal>
<returnvalue>t</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<type>anymultirange</type> <literal>&<</literal> <type>anyrange</type>
<returnvalue>boolean</returnvalue>
</para>
<para>
Does the multirange not extend to the right of the range?
</para>
<para>
<literal>'{[1,20)}'::int8multirange &< int8range(18,20)</literal>
<returnvalue>t</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<type>anyrange</type> <literal>&<</literal> <type>anymultirange</type>
<returnvalue>boolean</returnvalue>
</para>
<para>
Does the range not extend to the right of the multirange?
</para>
<para>
<literal>int8range(1,20) &< '{[18,20)}'::int8multirange</literal>
<returnvalue>t</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<type>anymultirange</type> <literal>&></literal> <type>anymultirange</type>
<returnvalue>boolean</returnvalue>
</para>
<para>
Does the first multirange not extend to the left of the second?
</para>
<para>
<literal>'{[7,20)}'::int8multirange &> '{[5,10)}'::int8multirange</literal>
<returnvalue>t</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<type>anymultirange</type> <literal>&></literal> <type>anyrange</type>
<returnvalue>boolean</returnvalue>
</para>
<para>
Does the multirange not extend to the left of the range?
</para>
<para>
<literal>'{[7,20)}'::int8multirange &> int8range(5,10)</literal>
<returnvalue>t</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<type>anyrange</type> <literal>&></literal> <type>anymultirange</type>
<returnvalue>boolean</returnvalue>
</para>
<para>
Does the range not extend to the left of the multirange?
</para>
<para>
<literal>int8range(7,20) &> '{[5,10)}'::int8multirange</literal>
<returnvalue>t</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<type>anymultirange</type> <literal>-|-</literal> <type>anymultirange</type>
<returnvalue>boolean</returnvalue>
</para>
<para>
Are the multiranges adjacent?
</para>
<para>
<literal>'{[1.1,2.2)}'::nummultirange -|- '{[2.2,3.3)}'::nummultirange</literal>
<returnvalue>t</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<type>anymultirange</type> <literal>-|-</literal> <type>anyrange</type>
<returnvalue>boolean</returnvalue>
</para>
<para>
Is the multirange adjacent to the range?
</para>
<para>
<literal>'{[1.1,2.2)}'::nummultirange -|- numrange(2.2,3.3)</literal>
<returnvalue>t</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<type>anyrange</type> <literal>-|-</literal> <type>anymultirange</type>
<returnvalue>boolean</returnvalue>
</para>
<para>
Is the range adjacent to the multirange?
</para>
<para>
<literal>numrange(1.1,2.2) -|- '{[2.2,3.3)}'::nummultirange</literal>
<returnvalue>t</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<type>anymultirange</type> <literal>+</literal> <type>anymultirange</type>
<returnvalue>anymultirange</returnvalue>
</para>
<para>
Computes the union of the multiranges. The multiranges need not overlap
or be adjacent.
</para>
<para>
<literal>'{[5,10)}'::nummultirange + '{[15,20)}'::nummultirange</literal>
<returnvalue>{[5,10), [15,20)}</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<type>anymultirange</type> <literal>*</literal> <type>anymultirange</type>
<returnvalue>anymultirange</returnvalue>
</para>
<para>
Computes the intersection of the multiranges.
</para>
<para>
<literal>'{[5,15)}'::int8multirange * '{[10,20)}'::int8multirange</literal>
<returnvalue>{[10,15)}</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<type>anymultirange</type> <literal>-</literal> <type>anymultirange</type>
<returnvalue>anymultirange</returnvalue>
</para>
<para>
Computes the difference of the multiranges.
</para>
<para>
<literal>'{[5,20)}'::int8multirange - '{[10,15)}'::int8multirange</literal>
<returnvalue>{[5,10), [15,20)}</returnvalue>
</para></entry>
</row>
</tbody>
</tgroup>
</table>
<para>
The left-of/right-of/adjacent operators always return false when an empty
range or multirange is involved; that is, an empty range is not considered to
be either before or after any other range.
</para>
<para>
Elsewhere empty ranges and multiranges are treated as the additive identity:
anything unioned with an empty value is itself. Anything minus an empty
value is itself. An empty multirange has exactly the same points as an empty
range. Every range contains the empty range. Every multirange contains as many
empty ranges as you like.
</para>
<para>
The range union and difference operators will fail if the resulting range would
need to contain two disjoint sub-ranges, as such a range cannot be
represented. There are separate operators for union and difference that take
multirange parameters and return a multirange, and they do not fail even if
their arguments are disjoint. So if you need a union or difference operation
for ranges that may be disjoint, you can avoid errors by first casting your
ranges to multiranges.
</para>
<para>
<xref linkend="range-functions-table"/> shows the functions
available for use with range types.
<xref linkend="multirange-functions-table"/> shows the functions
available for use with multirange types.
</para>
<table id="range-functions-table">
<title>Range Functions</title>
<tgroup cols="1">
<thead>
<row>
<entry role="func_table_entry"><para role="func_signature">
Function
</para>
<para>
Description
</para>
<para>
Example(s)
</para></entry>
</row>
</thead>
<tbody>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>lower</primary>
</indexterm>
<function>lower</function> ( <type>anyrange</type> )
<returnvalue>anyelement</returnvalue>
</para>
<para>
Extracts the lower bound of the range (<literal>NULL</literal> if the
range is empty or the lower bound is infinite).
</para>
<para>
<literal>lower(numrange(1.1,2.2))</literal>
<returnvalue>1.1</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>upper</primary>
</indexterm>
<function>upper</function> ( <type>anyrange</type> )
<returnvalue>anyelement</returnvalue>
</para>
<para>
Extracts the upper bound of the range (<literal>NULL</literal> if the
range is empty or the upper bound is infinite).
</para>
<para>
<literal>upper(numrange(1.1,2.2))</literal>
<returnvalue>2.2</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>isempty</primary>
</indexterm>
<function>isempty</function> ( <type>anyrange</type> )
<returnvalue>boolean</returnvalue>
</para>
<para>
Is the range empty?
</para>
<para>
<literal>isempty(numrange(1.1,2.2))</literal>
<returnvalue>f</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>lower_inc</primary>
</indexterm>
<function>lower_inc</function> ( <type>anyrange</type> )
<returnvalue>boolean</returnvalue>
</para>
<para>
Is the range's lower bound inclusive?
</para>
<para>
<literal>lower_inc(numrange(1.1,2.2))</literal>
<returnvalue>t</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>upper_inc</primary>
</indexterm>
<function>upper_inc</function> ( <type>anyrange</type> )
<returnvalue>boolean</returnvalue>
</para>
<para>
Is the range's upper bound inclusive?
</para>
<para>
<literal>upper_inc(numrange(1.1,2.2))</literal>
<returnvalue>f</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>lower_inf</primary>
</indexterm>
<function>lower_inf</function> ( <type>anyrange</type> )
<returnvalue>boolean</returnvalue>
</para>
<para>
Is the range's lower bound infinite?
</para>
<para>
<literal>lower_inf('(,)'::daterange)</literal>
<returnvalue>t</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>upper_inf</primary>
</indexterm>
<function>upper_inf</function> ( <type>anyrange</type> )
<returnvalue>boolean</returnvalue>
</para>
<para>
Is the range's upper bound infinite?
</para>
<para>
<literal>upper_inf('(,)'::daterange)</literal>
<returnvalue>t</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>range_merge</primary>
</indexterm>
<function>range_merge</function> ( <type>anyrange</type>, <type>anyrange</type> )
<returnvalue>anyrange</returnvalue>
</para>
<para>
Computes the smallest range that includes both of the given ranges.
</para>
<para>
<literal>range_merge('[1,2)'::int4range, '[3,4)'::int4range)</literal>
<returnvalue>[1,4)</returnvalue>
</para></entry>
</row>
</tbody>
</tgroup>
</table>
<table id="multirange-functions-table">
<title>Multirange Functions</title>
<tgroup cols="1">
<thead>
<row>
<entry role="func_table_entry"><para role="func_signature">
Function
</para>
<para>
Description
</para>
<para>
Example(s)
</para></entry>
</row>
</thead>
<tbody>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>lower</primary>
</indexterm>
<function>lower</function> ( <type>anymultirange</type> )
<returnvalue>anyelement</returnvalue>
</para>
<para>
Extracts the lower bound of the multirange (<literal>NULL</literal> if the
multirange is empty or the lower bound is infinite).
</para>
<para>
<literal>lower('{[1.1,2.2)}'::nummultirange)</literal>
<returnvalue>1.1</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>upper</primary>
</indexterm>
<function>upper</function> ( <type>anymultirange</type> )
<returnvalue>anyelement</returnvalue>
</para>
<para>
Extracts the upper bound of the multirange (<literal>NULL</literal> if the
multirange is empty or the upper bound is infinite).
</para>
<para>
<literal>upper('{[1.1,2.2)}'::nummultirange)</literal>
<returnvalue>2.2</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>isempty</primary>
</indexterm>
<function>isempty</function> ( <type>anymultirange</type> )
<returnvalue>boolean</returnvalue>
</para>
<para>
Is the multirange empty?
</para>
<para>
<literal>isempty('{[1.1,2.2)}'::nummultirange)</literal>
<returnvalue>f</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>lower_inc</primary>
</indexterm>
<function>lower_inc</function> ( <type>anymultirange</type> )
<returnvalue>boolean</returnvalue>
</para>
<para>
Is the multirange's lower bound inclusive?
</para>
<para>
<literal>lower_inc('{[1.1,2.2)}'::nummultirange)</literal>
<returnvalue>t</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>upper_inc</primary>
</indexterm>
<function>upper_inc</function> ( <type>anymultirange</type> )
<returnvalue>boolean</returnvalue>
</para>
<para>
Is the multirange's upper bound inclusive?
</para>
<para>
<literal>upper_inc('{[1.1,2.2)}'::nummultirange)</literal>
<returnvalue>f</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>lower_inf</primary>
</indexterm>
<function>lower_inf</function> ( <type>anymultirange</type> )
<returnvalue>boolean</returnvalue>
</para>
<para>
Is the multirange's lower bound infinite?
</para>
<para>
<literal>lower_inf('{(,)}'::datemultirange)</literal>
<returnvalue>t</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>upper_inf</primary>
</indexterm>
<function>upper_inf</function> ( <type>anymultirange</type> )
<returnvalue>boolean</returnvalue>
</para>
<para>
Is the multirange's upper bound infinite?
</para>
<para>
<literal>upper_inf('{(,)}'::datemultirange)</literal>
<returnvalue>t</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>range_merge</primary>
</indexterm>
<function>range_merge</function> ( <type>anymultirange</type> )
<returnvalue>anyrange</returnvalue>
</para>
<para>
Computes the smallest range that includes the entire multirange.
</para>
<para>
<literal>range_merge('{[1,2), [3,4)}'::int4multirange)</literal>
<returnvalue>[1,4)</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>multirange (function)</primary>
</indexterm>
<function>multirange</function> ( <type>anyrange</type> )
<returnvalue>anymultirange</returnvalue>
</para>
<para>
Returns a multirange containing just the given range.
</para>
<para>
<literal>multirange('[1,2)'::int4range)</literal>
<returnvalue>{[1,2)}</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>unnest</primary>
<secondary>for multirange</secondary>
</indexterm>
<function>unnest</function> ( <type>anymultirange</type> )
<returnvalue>setof anyrange</returnvalue>
</para>
<para>
Expands a multirange into a set of ranges.
The ranges are read out in storage order (ascending).
</para>
<para>
<literal>unnest('{[1,2), [3,4)}'::int4multirange)</literal>
<returnvalue></returnvalue>
<programlisting>
[1,2)
[3,4)
</programlisting>
</para></entry>
</row>
</tbody>
</tgroup>
</table>
<para>
The <function>lower_inc</function>, <function>upper_inc</function>,
<function>lower_inf</function>, and <function>upper_inf</function>
functions all return false for an empty range or multirange.
</para>
</sect1>
<sect1 id="functions-aggregate">
<title>Aggregate Functions</title>
<indexterm zone="functions-aggregate">
<primary>aggregate function</primary>
<secondary>built-in</secondary>
</indexterm>
<para>
<firstterm>Aggregate functions</firstterm> compute a single result
from a set of input values. The built-in general-purpose aggregate
functions are listed in <xref linkend="functions-aggregate-table"/>
while statistical aggregates are in <xref
linkend="functions-aggregate-statistics-table"/>.
The built-in within-group ordered-set aggregate functions
are listed in <xref linkend="functions-orderedset-table"/>
while the built-in within-group hypothetical-set ones are in <xref
linkend="functions-hypothetical-table"/>. Grouping operations,
which are closely related to aggregate functions, are listed in
<xref linkend="functions-grouping-table"/>.
The special syntax considerations for aggregate
functions are explained in <xref linkend="syntax-aggregates"/>.
Consult <xref linkend="tutorial-agg"/> for additional introductory
information.
</para>
<para>
Aggregate functions that support <firstterm>Partial Mode</firstterm>
are eligible to participate in various optimizations, such as parallel
aggregation.
</para>
<table id="functions-aggregate-table">
<title>General-Purpose Aggregate Functions</title>
<tgroup cols="2">
<colspec colname="col1" colwidth="10*"/>
<colspec colname="col2" colwidth="1*"/>
<thead>
<row>
<entry role="func_table_entry"><para role="func_signature">
Function
</para>
<para>
Description
</para></entry>
<entry>Partial Mode</entry>
</row>
</thead>
<tbody>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>array_agg</primary>
</indexterm>
<function>array_agg</function> ( <type>anynonarray</type> )
<returnvalue>anyarray</returnvalue>
</para>
<para>
Collects all the input values, including nulls, into an array.
</para></entry>
<entry>No</entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<function>array_agg</function> ( <type>anyarray</type> )
<returnvalue>anyarray</returnvalue>
</para>
<para>
Concatenates all the input arrays into an array of one higher
dimension. (The inputs must all have the same dimensionality, and
cannot be empty or null.)
</para></entry>
<entry>No</entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>average</primary>
</indexterm>
<indexterm>
<primary>avg</primary>
</indexterm>
<function>avg</function> ( <type>smallint</type> )
<returnvalue>numeric</returnvalue>
</para>
<para role="func_signature">
<function>avg</function> ( <type>integer</type> )
<returnvalue>numeric</returnvalue>
</para>
<para role="func_signature">
<function>avg</function> ( <type>bigint</type> )
<returnvalue>numeric</returnvalue>
</para>
<para role="func_signature">
<function>avg</function> ( <type>numeric</type> )
<returnvalue>numeric</returnvalue>
</para>
<para role="func_signature">
<function>avg</function> ( <type>real</type> )
<returnvalue>double precision</returnvalue>
</para>
<para role="func_signature">
<function>avg</function> ( <type>double precision</type> )
<returnvalue>double precision</returnvalue>
</para>
<para role="func_signature">
<function>avg</function> ( <type>interval</type> )
<returnvalue>interval</returnvalue>
</para>
<para>
Computes the average (arithmetic mean) of all the non-null input
values.
</para></entry>
<entry>Yes</entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>bit_and</primary>
</indexterm>
<function>bit_and</function> ( <type>smallint</type> )
<returnvalue>smallint</returnvalue>
</para>
<para role="func_signature">
<function>bit_and</function> ( <type>integer</type> )
<returnvalue>integer</returnvalue>
</para>
<para role="func_signature">
<function>bit_and</function> ( <type>bigint</type> )
<returnvalue>bigint</returnvalue>
</para>
<para role="func_signature">
<function>bit_and</function> ( <type>bit</type> )
<returnvalue>bit</returnvalue>
</para>
<para>
Computes the bitwise AND of all non-null input values.
</para></entry>
<entry>Yes</entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>bit_or</primary>
</indexterm>
<function>bit_or</function> ( <type>smallint</type> )
<returnvalue>smallint</returnvalue>
</para>
<para role="func_signature">
<function>bit_or</function> ( <type>integer</type> )
<returnvalue>integer</returnvalue>
</para>
<para role="func_signature">
<function>bit_or</function> ( <type>bigint</type> )
<returnvalue>bigint</returnvalue>
</para>
<para role="func_signature">
<function>bit_or</function> ( <type>bit</type> )
<returnvalue>bit</returnvalue>
</para>
<para>
Computes the bitwise OR of all non-null input values.
</para></entry>
<entry>Yes</entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>bit_xor</primary>
</indexterm>
<function>bit_xor</function> ( <type>smallint</type> )
<returnvalue>smallint</returnvalue>
</para>
<para role="func_signature">
<function>bit_xor</function> ( <type>integer</type> )
<returnvalue>integer</returnvalue>
</para>
<para role="func_signature">
<function>bit_xor</function> ( <type>bigint</type> )
<returnvalue>bigint</returnvalue>
</para>
<para role="func_signature">
<function>bit_xor</function> ( <type>bit</type> )
<returnvalue>bit</returnvalue>
</para>
<para>
Computes the bitwise exclusive OR of all non-null input values.
Can be useful as a checksum for an unordered set of values.
</para></entry>
<entry>Yes</entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>bool_and</primary>
</indexterm>
<function>bool_and</function> ( <type>boolean</type> )
<returnvalue>boolean</returnvalue>
</para>
<para>
Returns true if all non-null input values are true, otherwise false.
</para></entry>
<entry>Yes</entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>bool_or</primary>
</indexterm>
<function>bool_or</function> ( <type>boolean</type> )
<returnvalue>boolean</returnvalue>
</para>
<para>
Returns true if any non-null input value is true, otherwise false.
</para></entry>
<entry>Yes</entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>count</primary>
</indexterm>
<function>count</function> ( <literal>*</literal> )
<returnvalue>bigint</returnvalue>
</para>
<para>
Computes the number of input rows.
</para></entry>
<entry>Yes</entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<function>count</function> ( <type>"any"</type> )
<returnvalue>bigint</returnvalue>
</para>
<para>
Computes the number of input rows in which the input value is not
null.
</para></entry>
<entry>Yes</entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>every</primary>
</indexterm>
<function>every</function> ( <type>boolean</type> )
<returnvalue>boolean</returnvalue>
</para>
<para>
This is the SQL standard's equivalent to <function>bool_and</function>.
</para></entry>
<entry>Yes</entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>json_agg</primary>
</indexterm>
<function>json_agg</function> ( <type>anyelement</type> )
<returnvalue>json</returnvalue>
</para>
<para role="func_signature">
<indexterm>
<primary>jsonb_agg</primary>
</indexterm>
<function>jsonb_agg</function> ( <type>anyelement</type> )
<returnvalue>jsonb</returnvalue>
</para>
<para>
Collects all the input values, including nulls, into a JSON array.
Values are converted to JSON as per <function>to_json</function>
or <function>to_jsonb</function>.
</para></entry>
<entry>No</entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>json_object_agg</primary>
</indexterm>
<function>json_object_agg</function> ( <parameter>key</parameter>
<type>"any"</type>, <parameter>value</parameter>
<type>"any"</type> )
<returnvalue>json</returnvalue>
</para>
<para role="func_signature">
<indexterm>
<primary>jsonb_object_agg</primary>
</indexterm>
<function>jsonb_object_agg</function> ( <parameter>key</parameter>
<type>"any"</type>, <parameter>value</parameter>
<type>"any"</type> )
<returnvalue>jsonb</returnvalue>
</para>
<para>
Collects all the key/value pairs into a JSON object. Key arguments
are coerced to text; value arguments are converted as
per <function>to_json</function> or <function>to_jsonb</function>.
Values can be null, but not keys.
</para></entry>
<entry>No</entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>max</primary>
</indexterm>
<function>max</function> ( <replaceable>see text</replaceable> )
<returnvalue><replaceable>same as input type</replaceable></returnvalue>
</para>
<para>
Computes the maximum of the non-null input
values. Available for any numeric, string, date/time, or enum type,
as well as <type>inet</type>, <type>interval</type>,
<type>money</type>, <type>oid</type>, <type>pg_lsn</type>,
<type>tid</type>,
and arrays of any of these types.
</para></entry>
<entry>Yes</entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>min</primary>
</indexterm>
<function>min</function> ( <replaceable>see text</replaceable> )
<returnvalue><replaceable>same as input type</replaceable></returnvalue>
</para>
<para>
Computes the minimum of the non-null input
values. Available for any numeric, string, date/time, or enum type,
as well as <type>inet</type>, <type>interval</type>,
<type>money</type>, <type>oid</type>, <type>pg_lsn</type>,
<type>tid</type>,
and arrays of any of these types.
</para></entry>
<entry>Yes</entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>range_agg</primary>
</indexterm>
<function>range_agg</function> ( <parameter>value</parameter>
<type>anyrange</type> )
<returnvalue>anymultirange</returnvalue>
</para>
<para>
Computes the union of the non-null input values.
</para></entry>
<entry>No</entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>range_intersect_agg</primary>
</indexterm>
<function>range_intersect_agg</function> ( <parameter>value</parameter>
<type>anyrange</type> )
<returnvalue>anymultirange</returnvalue>
</para>
<para>
Computes the intersection of the non-null input values.
</para></entry>
<entry>No</entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>string_agg</primary>
</indexterm>
<function>string_agg</function> ( <parameter>value</parameter>
<type>text</type>, <parameter>delimiter</parameter> <type>text</type> )
<returnvalue>text</returnvalue>
</para>
<para role="func_signature">
<function>string_agg</function> ( <parameter>value</parameter>
<type>bytea</type>, <parameter>delimiter</parameter> <type>bytea</type> )
<returnvalue>bytea</returnvalue>
</para>
<para>
Concatenates the non-null input values into a string. Each value
after the first is preceded by the
corresponding <parameter>delimiter</parameter> (if it's not null).
</para></entry>
<entry>No</entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>sum</primary>
</indexterm>
<function>sum</function> ( <type>smallint</type> )
<returnvalue>bigint</returnvalue>
</para>
<para role="func_signature">
<function>sum</function> ( <type>integer</type> )
<returnvalue>bigint</returnvalue>
</para>
<para role="func_signature">
<function>sum</function> ( <type>bigint</type> )
<returnvalue>numeric</returnvalue>
</para>
<para role="func_signature">
<function>sum</function> ( <type>numeric</type> )
<returnvalue>numeric</returnvalue>
</para>
<para role="func_signature">
<function>sum</function> ( <type>real</type> )
<returnvalue>real</returnvalue>
</para>
<para role="func_signature">
<function>sum</function> ( <type>double precision</type> )
<returnvalue>double precision</returnvalue>
</para>
<para role="func_signature">
<function>sum</function> ( <type>interval</type> )
<returnvalue>interval</returnvalue>
</para>
<para role="func_signature">
<function>sum</function> ( <type>money</type> )
<returnvalue>money</returnvalue>
</para>
<para>
Computes the sum of the non-null input values.
</para></entry>
<entry>Yes</entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>xmlagg</primary>
</indexterm>
<function>xmlagg</function> ( <type>xml</type> )
<returnvalue>xml</returnvalue>
</para>
<para>
Concatenates the non-null XML input values (see
<xref linkend="functions-xml-xmlagg"/>).
</para></entry>
<entry>No</entry>
</row>
</tbody>
</tgroup>
</table>
<para>
It should be noted that except for <function>count</function>,
these functions return a null value when no rows are selected. In
particular, <function>sum</function> of no rows returns null, not
zero as one might expect, and <function>array_agg</function>
returns null rather than an empty array when there are no input
rows. The <function>coalesce</function> function can be used to
substitute zero or an empty array for null when necessary.
</para>
<para>
The aggregate functions <function>array_agg</function>,
<function>json_agg</function>, <function>jsonb_agg</function>,
<function>json_object_agg</function>, <function>jsonb_object_agg</function>,
<function>string_agg</function>,
and <function>xmlagg</function>, as well as similar user-defined
aggregate functions, produce meaningfully different result values
depending on the order of the input values. This ordering is
unspecified by default, but can be controlled by writing an
<literal>ORDER BY</literal> clause within the aggregate call, as shown in
<xref linkend="syntax-aggregates"/>.
Alternatively, supplying the input values from a sorted subquery
will usually work. For example:
<screen><![CDATA[
SELECT xmlagg(x) FROM (SELECT x FROM test ORDER BY y DESC) AS tab;
]]></screen>
Beware that this approach can fail if the outer query level contains
additional processing, such as a join, because that might cause the
subquery's output to be reordered before the aggregate is computed.
</para>
<note>
<indexterm>
<primary>ANY</primary>
</indexterm>
<indexterm>
<primary>SOME</primary>
</indexterm>
<para>
The boolean aggregates <function>bool_and</function> and
<function>bool_or</function> correspond to the standard SQL aggregates
<function>every</function> and <function>any</function> or
<function>some</function>.
<productname>PostgreSQL</productname>
supports <function>every</function>, but not <function>any</function>
or <function>some</function>, because there is an ambiguity built into
the standard syntax:
<programlisting>
SELECT b1 = ANY((SELECT b2 FROM t2 ...)) FROM t1 ...;
</programlisting>
Here <function>ANY</function> can be considered either as introducing
a subquery, or as being an aggregate function, if the subquery
returns one row with a Boolean value.
Thus the standard name cannot be given to these aggregates.
</para>
</note>
<note>
<para>
Users accustomed to working with other SQL database management
systems might be disappointed by the performance of the
<function>count</function> aggregate when it is applied to the
entire table. A query like:
<programlisting>
SELECT count(*) FROM sometable;
</programlisting>
will require effort proportional to the size of the table:
<productname>PostgreSQL</productname> will need to scan either the
entire table or the entirety of an index that includes all rows in
the table.
</para>
</note>
<para>
<xref linkend="functions-aggregate-statistics-table"/> shows
aggregate functions typically used in statistical analysis.
(These are separated out merely to avoid cluttering the listing
of more-commonly-used aggregates.) Functions shown as
accepting <replaceable>numeric_type</replaceable> are available for all
the types <type>smallint</type>, <type>integer</type>,
<type>bigint</type>, <type>numeric</type>, <type>real</type>,
and <type>double precision</type>.
Where the description mentions
<parameter>N</parameter>, it means the
number of input rows for which all the input expressions are non-null.
In all cases, null is returned if the computation is meaningless,
for example when <parameter>N</parameter> is zero.
</para>
<indexterm>
<primary>statistics</primary>
</indexterm>
<indexterm>
<primary>linear regression</primary>
</indexterm>
<table id="functions-aggregate-statistics-table">
<title>Aggregate Functions for Statistics</title>
<tgroup cols="2">
<colspec colname="col1" colwidth="10*"/>
<colspec colname="col2" colwidth="1*"/>
<thead>
<row>
<entry role="func_table_entry"><para role="func_signature">
Function
</para>
<para>
Description
</para></entry>
<entry>Partial Mode</entry>
</row>
</thead>
<tbody>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>correlation</primary>
</indexterm>
<indexterm>
<primary>corr</primary>
</indexterm>
<function>corr</function> ( <parameter>Y</parameter> <type>double precision</type>, <parameter>X</parameter> <type>double precision</type> )
<returnvalue>double precision</returnvalue>
</para>
<para>
Computes the correlation coefficient.
</para></entry>
<entry>Yes</entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>covariance</primary>
<secondary>population</secondary>
</indexterm>
<indexterm>
<primary>covar_pop</primary>
</indexterm>
<function>covar_pop</function> ( <parameter>Y</parameter> <type>double precision</type>, <parameter>X</parameter> <type>double precision</type> )
<returnvalue>double precision</returnvalue>
</para>
<para>
Computes the population covariance.
</para></entry>
<entry>Yes</entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>covariance</primary>
<secondary>sample</secondary>
</indexterm>
<indexterm>
<primary>covar_samp</primary>
</indexterm>
<function>covar_samp</function> ( <parameter>Y</parameter> <type>double precision</type>, <parameter>X</parameter> <type>double precision</type> )
<returnvalue>double precision</returnvalue>
</para>
<para>
Computes the sample covariance.
</para></entry>
<entry>Yes</entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>regr_avgx</primary>
</indexterm>
<function>regr_avgx</function> ( <parameter>Y</parameter> <type>double precision</type>, <parameter>X</parameter> <type>double precision</type> )
<returnvalue>double precision</returnvalue>
</para>
<para>
Computes the average of the independent variable,
<literal>sum(<parameter>X</parameter>)/<parameter>N</parameter></literal>.
</para></entry>
<entry>Yes</entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>regr_avgy</primary>
</indexterm>
<function>regr_avgy</function> ( <parameter>Y</parameter> <type>double precision</type>, <parameter>X</parameter> <type>double precision</type> )
<returnvalue>double precision</returnvalue>
</para>
<para>
Computes the average of the dependent variable,
<literal>sum(<parameter>Y</parameter>)/<parameter>N</parameter></literal>.
</para></entry>
<entry>Yes</entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>regr_count</primary>
</indexterm>
<function>regr_count</function> ( <parameter>Y</parameter> <type>double precision</type>, <parameter>X</parameter> <type>double precision</type> )
<returnvalue>bigint</returnvalue>
</para>
<para>
Computes the number of rows in which both inputs are non-null.
</para></entry>
<entry>Yes</entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>regression intercept</primary>
</indexterm>
<indexterm>
<primary>regr_intercept</primary>
</indexterm>
<function>regr_intercept</function> ( <parameter>Y</parameter> <type>double precision</type>, <parameter>X</parameter> <type>double precision</type> )
<returnvalue>double precision</returnvalue>
</para>
<para>
Computes the y-intercept of the least-squares-fit linear equation
determined by the
(<parameter>X</parameter>, <parameter>Y</parameter>) pairs.
</para></entry>
<entry>Yes</entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>regr_r2</primary>
</indexterm>
<function>regr_r2</function> ( <parameter>Y</parameter> <type>double precision</type>, <parameter>X</parameter> <type>double precision</type> )
<returnvalue>double precision</returnvalue>
</para>
<para>
Computes the square of the correlation coefficient.
</para></entry>
<entry>Yes</entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>regression slope</primary>
</indexterm>
<indexterm>
<primary>regr_slope</primary>
</indexterm>
<function>regr_slope</function> ( <parameter>Y</parameter> <type>double precision</type>, <parameter>X</parameter> <type>double precision</type> )
<returnvalue>double precision</returnvalue>
</para>
<para>
Computes the slope of the least-squares-fit linear equation determined
by the (<parameter>X</parameter>, <parameter>Y</parameter>)
pairs.
</para></entry>
<entry>Yes</entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>regr_sxx</primary>
</indexterm>
<function>regr_sxx</function> ( <parameter>Y</parameter> <type>double precision</type>, <parameter>X</parameter> <type>double precision</type> )
<returnvalue>double precision</returnvalue>
</para>
<para>
Computes the <quote>sum of squares</quote> of the independent
variable,
<literal>sum(<parameter>X</parameter>^2) - sum(<parameter>X</parameter>)^2/<parameter>N</parameter></literal>.
</para></entry>
<entry>Yes</entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>regr_sxy</primary>
</indexterm>
<function>regr_sxy</function> ( <parameter>Y</parameter> <type>double precision</type>, <parameter>X</parameter> <type>double precision</type> )
<returnvalue>double precision</returnvalue>
</para>
<para>
Computes the <quote>sum of products</quote> of independent times
dependent variables,
<literal>sum(<parameter>X</parameter>*<parameter>Y</parameter>) - sum(<parameter>X</parameter>) * sum(<parameter>Y</parameter>)/<parameter>N</parameter></literal>.
</para></entry>
<entry>Yes</entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>regr_syy</primary>
</indexterm>
<function>regr_syy</function> ( <parameter>Y</parameter> <type>double precision</type>, <parameter>X</parameter> <type>double precision</type> )
<returnvalue>double precision</returnvalue>
</para>
<para>
Computes the <quote>sum of squares</quote> of the dependent
variable,
<literal>sum(<parameter>Y</parameter>^2) - sum(<parameter>Y</parameter>)^2/<parameter>N</parameter></literal>.
</para></entry>
<entry>Yes</entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>standard deviation</primary>
</indexterm>
<indexterm>
<primary>stddev</primary>
</indexterm>
<function>stddev</function> ( <replaceable>numeric_type</replaceable> )
<returnvalue></returnvalue> <type>double precision</type>
for <type>real</type> or <type>double precision</type>,
otherwise <type>numeric</type>
</para>
<para>
This is a historical alias for <function>stddev_samp</function>.
</para></entry>
<entry>Yes</entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>standard deviation</primary>
<secondary>population</secondary>
</indexterm>
<indexterm>
<primary>stddev_pop</primary>
</indexterm>
<function>stddev_pop</function> ( <replaceable>numeric_type</replaceable> )
<returnvalue></returnvalue> <type>double precision</type>
for <type>real</type> or <type>double precision</type>,
otherwise <type>numeric</type>
</para>
<para>
Computes the population standard deviation of the input values.
</para></entry>
<entry>Yes</entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>standard deviation</primary>
<secondary>sample</secondary>
</indexterm>
<indexterm>
<primary>stddev_samp</primary>
</indexterm>
<function>stddev_samp</function> ( <replaceable>numeric_type</replaceable> )
<returnvalue></returnvalue> <type>double precision</type>
for <type>real</type> or <type>double precision</type>,
otherwise <type>numeric</type>
</para>
<para>
Computes the sample standard deviation of the input values.
</para></entry>
<entry>Yes</entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>variance</primary>
</indexterm>
<function>variance</function> ( <replaceable>numeric_type</replaceable> )
<returnvalue></returnvalue> <type>double precision</type>
for <type>real</type> or <type>double precision</type>,
otherwise <type>numeric</type>
</para>
<para>
This is a historical alias for <function>var_samp</function>.
</para></entry>
<entry>Yes</entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>variance</primary>
<secondary>population</secondary>
</indexterm>
<indexterm>
<primary>var_pop</primary>
</indexterm>
<function>var_pop</function> ( <replaceable>numeric_type</replaceable> )
<returnvalue></returnvalue> <type>double precision</type>
for <type>real</type> or <type>double precision</type>,
otherwise <type>numeric</type>
</para>
<para>
Computes the population variance of the input values (square of the
population standard deviation).
</para></entry>
<entry>Yes</entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>variance</primary>
<secondary>sample</secondary>
</indexterm>
<indexterm>
<primary>var_samp</primary>
</indexterm>
<function>var_samp</function> ( <replaceable>numeric_type</replaceable> )
<returnvalue></returnvalue> <type>double precision</type>
for <type>real</type> or <type>double precision</type>,
otherwise <type>numeric</type>
</para>
<para>
Computes the sample variance of the input values (square of the sample
standard deviation).
</para></entry>
<entry>Yes</entry>
</row>
</tbody>
</tgroup>
</table>
<para>
<xref linkend="functions-orderedset-table"/> shows some
aggregate functions that use the <firstterm>ordered-set aggregate</firstterm>
syntax. These functions are sometimes referred to as <quote>inverse
distribution</quote> functions. Their aggregated input is introduced by
<literal>ORDER BY</literal>, and they may also take a <firstterm>direct
argument</firstterm> that is not aggregated, but is computed only once.
All these functions ignore null values in their aggregated input.
For those that take a <parameter>fraction</parameter> parameter, the
fraction value must be between 0 and 1; an error is thrown if not.
However, a null <parameter>fraction</parameter> value simply produces a
null result.
</para>
<indexterm>
<primary>ordered-set aggregate</primary>
<secondary>built-in</secondary>
</indexterm>
<indexterm>
<primary>inverse distribution</primary>
</indexterm>
<table id="functions-orderedset-table">
<title>Ordered-Set Aggregate Functions</title>
<tgroup cols="2">
<colspec colname="col1" colwidth="10*"/>
<colspec colname="col2" colwidth="1*"/>
<thead>
<row>
<entry role="func_table_entry"><para role="func_signature">
Function
</para>
<para>
Description
</para></entry>
<entry>Partial Mode</entry>
</row>
</thead>
<tbody>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>mode</primary>
<secondary>statistical</secondary>
</indexterm>
<function>mode</function> () <literal>WITHIN GROUP</literal> ( <literal>ORDER BY</literal> <type>anyelement</type> )
<returnvalue>anyelement</returnvalue>
</para>
<para>
Computes the <firstterm>mode</firstterm>, the most frequent
value of the aggregated argument (arbitrarily choosing the first one
if there are multiple equally-frequent values). The aggregated
argument must be of a sortable type.
</para></entry>
<entry>No</entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>percentile</primary>
<secondary>continuous</secondary>
</indexterm>
<function>percentile_cont</function> ( <parameter>fraction</parameter> <type>double precision</type> ) <literal>WITHIN GROUP</literal> ( <literal>ORDER BY</literal> <type>double precision</type> )
<returnvalue>double precision</returnvalue>
</para>
<para role="func_signature">
<function>percentile_cont</function> ( <parameter>fraction</parameter> <type>double precision</type> ) <literal>WITHIN GROUP</literal> ( <literal>ORDER BY</literal> <type>interval</type> )
<returnvalue>interval</returnvalue>
</para>
<para>
Computes the <firstterm>continuous percentile</firstterm>, a value
corresponding to the specified <parameter>fraction</parameter>
within the ordered set of aggregated argument values. This will
interpolate between adjacent input items if needed.
</para></entry>
<entry>No</entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<function>percentile_cont</function> ( <parameter>fractions</parameter> <type>double precision[]</type> ) <literal>WITHIN GROUP</literal> ( <literal>ORDER BY</literal> <type>double precision</type> )
<returnvalue>double precision[]</returnvalue>
</para>
<para role="func_signature">
<function>percentile_cont</function> ( <parameter>fractions</parameter> <type>double precision[]</type> ) <literal>WITHIN GROUP</literal> ( <literal>ORDER BY</literal> <type>interval</type> )
<returnvalue>interval[]</returnvalue>
</para>
<para>
Computes multiple continuous percentiles. The result is an array of
the same dimensions as the <parameter>fractions</parameter>
parameter, with each non-null element replaced by the (possibly
interpolated) value corresponding to that percentile.
</para></entry>
<entry>No</entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>percentile</primary>
<secondary>discrete</secondary>
</indexterm>
<function>percentile_disc</function> ( <parameter>fraction</parameter> <type>double precision</type> ) <literal>WITHIN GROUP</literal> ( <literal>ORDER BY</literal> <type>anyelement</type> )
<returnvalue>anyelement</returnvalue>
</para>
<para>
Computes the <firstterm>discrete percentile</firstterm>, the first
value within the ordered set of aggregated argument values whose
position in the ordering equals or exceeds the
specified <parameter>fraction</parameter>. The aggregated
argument must be of a sortable type.
</para></entry>
<entry>No</entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<function>percentile_disc</function> ( <parameter>fractions</parameter> <type>double precision[]</type> ) <literal>WITHIN GROUP</literal> ( <literal>ORDER BY</literal> <type>anyelement</type> )
<returnvalue>anyarray</returnvalue>
</para>
<para>
Computes multiple discrete percentiles. The result is an array of the
same dimensions as the <parameter>fractions</parameter> parameter,
with each non-null element replaced by the input value corresponding
to that percentile.
The aggregated argument must be of a sortable type.
</para></entry>
<entry>No</entry>
</row>
</tbody>
</tgroup>
</table>
<indexterm>
<primary>hypothetical-set aggregate</primary>
<secondary>built-in</secondary>
</indexterm>
<para>
Each of the <quote>hypothetical-set</quote> aggregates listed in
<xref linkend="functions-hypothetical-table"/> is associated with a
window function of the same name defined in
<xref linkend="functions-window"/>. In each case, the aggregate's result
is the value that the associated window function would have
returned for the <quote>hypothetical</quote> row constructed from
<replaceable>args</replaceable>, if such a row had been added to the sorted
group of rows represented by the <replaceable>sorted_args</replaceable>.
For each of these functions, the list of direct arguments
given in <replaceable>args</replaceable> must match the number and types of
the aggregated arguments given in <replaceable>sorted_args</replaceable>.
Unlike most built-in aggregates, these aggregates are not strict, that is
they do not drop input rows containing nulls. Null values sort according
to the rule specified in the <literal>ORDER BY</literal> clause.
</para>
<table id="functions-hypothetical-table">
<title>Hypothetical-Set Aggregate Functions</title>
<tgroup cols="2">
<colspec colname="col1" colwidth="10*"/>
<colspec colname="col2" colwidth="1*"/>
<thead>
<row>
<entry role="func_table_entry"><para role="func_signature">
Function
</para>
<para>
Description
</para></entry>
<entry>Partial Mode</entry>
</row>
</thead>
<tbody>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>rank</primary>
<secondary>hypothetical</secondary>
</indexterm>
<function>rank</function> ( <replaceable>args</replaceable> ) <literal>WITHIN GROUP</literal> ( <literal>ORDER BY</literal> <replaceable>sorted_args</replaceable> )
<returnvalue>bigint</returnvalue>
</para>
<para>
Computes the rank of the hypothetical row, with gaps; that is, the row
number of the first row in its peer group.
</para></entry>
<entry>No</entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>dense_rank</primary>
<secondary>hypothetical</secondary>
</indexterm>
<function>dense_rank</function> ( <replaceable>args</replaceable> ) <literal>WITHIN GROUP</literal> ( <literal>ORDER BY</literal> <replaceable>sorted_args</replaceable> )
<returnvalue>bigint</returnvalue>
</para>
<para>
Computes the rank of the hypothetical row, without gaps; this function
effectively counts peer groups.
</para></entry>
<entry>No</entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>percent_rank</primary>
<secondary>hypothetical</secondary>
</indexterm>
<function>percent_rank</function> ( <replaceable>args</replaceable> ) <literal>WITHIN GROUP</literal> ( <literal>ORDER BY</literal> <replaceable>sorted_args</replaceable> )
<returnvalue>double precision</returnvalue>
</para>
<para>
Computes the relative rank of the hypothetical row, that is
(<function>rank</function> - 1) / (total rows - 1).
The value thus ranges from 0 to 1 inclusive.
</para></entry>
<entry>No</entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>cume_dist</primary>
<secondary>hypothetical</secondary>
</indexterm>
<function>cume_dist</function> ( <replaceable>args</replaceable> ) <literal>WITHIN GROUP</literal> ( <literal>ORDER BY</literal> <replaceable>sorted_args</replaceable> )
<returnvalue>double precision</returnvalue>
</para>
<para>
Computes the cumulative distribution, that is (number of rows
preceding or peers with hypothetical row) / (total rows). The value
thus ranges from 1/<parameter>N</parameter> to 1.
</para></entry>
<entry>No</entry>
</row>
</tbody>
</tgroup>
</table>
<table id="functions-grouping-table">
<title>Grouping Operations</title>
<tgroup cols="1">
<thead>
<row>
<entry role="func_table_entry"><para role="func_signature">
Function
</para>
<para>
Description
</para></entry>
</row>
</thead>
<tbody>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>GROUPING</primary>
</indexterm>
<function>GROUPING</function> ( <replaceable>group_by_expression(s)</replaceable> )
<returnvalue>integer</returnvalue>
</para>
<para>
Returns a bit mask indicating which <literal>GROUP BY</literal>
expressions are not included in the current grouping set.
Bits are assigned with the rightmost argument corresponding to the
least-significant bit; each bit is 0 if the corresponding expression
is included in the grouping criteria of the grouping set generating
the current result row, and 1 if it is not included.
</para></entry>
</row>
</tbody>
</tgroup>
</table>
<para>
The grouping operations shown in
<xref linkend="functions-grouping-table"/> are used in conjunction with
grouping sets (see <xref linkend="queries-grouping-sets"/>) to distinguish
result rows. The arguments to the <literal>GROUPING</literal> function
are not actually evaluated, but they must exactly match expressions given
in the <literal>GROUP BY</literal> clause of the associated query level.
For example:
<screen>
<prompt>=></prompt> <userinput>SELECT * FROM items_sold;</userinput>
make | model | sales
-------+-------+-------
Foo | GT | 10
Foo | Tour | 20
Bar | City | 15
Bar | Sport | 5
(4 rows)
<prompt>=></prompt> <userinput>SELECT make, model, GROUPING(make,model), sum(sales) FROM items_sold GROUP BY ROLLUP(make,model);</userinput>
make | model | grouping | sum
-------+-------+----------+-----
Foo | GT | 0 | 10
Foo | Tour | 0 | 20
Bar | City | 0 | 15
Bar | Sport | 0 | 5
Foo | | 1 | 30
Bar | | 1 | 20
| | 3 | 50
(7 rows)
</screen>
Here, the <literal>grouping</literal> value <literal>0</literal> in the
first four rows shows that those have been grouped normally, over both the
grouping columns. The value <literal>1</literal> indicates
that <literal>model</literal> was not grouped by in the next-to-last two
rows, and the value <literal>3</literal> indicates that
neither <literal>make</literal> nor <literal>model</literal> was grouped
by in the last row (which therefore is an aggregate over all the input
rows).
</para>
</sect1>
<sect1 id="functions-window">
<title>Window Functions</title>
<indexterm zone="functions-window">
<primary>window function</primary>
<secondary>built-in</secondary>
</indexterm>
<para>
<firstterm>Window functions</firstterm> provide the ability to perform
calculations across sets of rows that are related to the current query
row. See <xref linkend="tutorial-window"/> for an introduction to this
feature, and <xref linkend="syntax-window-functions"/> for syntax
details.
</para>
<para>
The built-in window functions are listed in
<xref linkend="functions-window-table"/>. Note that these functions
<emphasis>must</emphasis> be invoked using window function syntax, i.e., an
<literal>OVER</literal> clause is required.
</para>
<para>
In addition to these functions, any built-in or user-defined
ordinary aggregate (i.e., not ordered-set or hypothetical-set aggregates)
can be used as a window function; see
<xref linkend="functions-aggregate"/> for a list of the built-in aggregates.
Aggregate functions act as window functions only when an <literal>OVER</literal>
clause follows the call; otherwise they act as plain aggregates
and return a single row for the entire set.
</para>
<table id="functions-window-table">
<title>General-Purpose Window Functions</title>
<tgroup cols="1">
<thead>
<row>
<entry role="func_table_entry"><para role="func_signature">
Function
</para>
<para>
Description
</para></entry>
</row>
</thead>
<tbody>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>row_number</primary>
</indexterm>
<function>row_number</function> ()
<returnvalue>bigint</returnvalue>
</para>
<para>
Returns the number of the current row within its partition, counting
from 1.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>rank</primary>
</indexterm>
<function>rank</function> ()
<returnvalue>bigint</returnvalue>
</para>
<para>
Returns the rank of the current row, with gaps; that is,
the <function>row_number</function> of the first row in its peer
group.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>dense_rank</primary>
</indexterm>
<function>dense_rank</function> ()
<returnvalue>bigint</returnvalue>
</para>
<para>
Returns the rank of the current row, without gaps; this function
effectively counts peer groups.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>percent_rank</primary>
</indexterm>
<function>percent_rank</function> ()
<returnvalue>double precision</returnvalue>
</para>
<para>
Returns the relative rank of the current row, that is
(<function>rank</function> - 1) / (total partition rows - 1).
The value thus ranges from 0 to 1 inclusive.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>cume_dist</primary>
</indexterm>
<function>cume_dist</function> ()
<returnvalue>double precision</returnvalue>
</para>
<para>
Returns the cumulative distribution, that is (number of partition rows
preceding or peers with current row) / (total partition rows).
The value thus ranges from 1/<parameter>N</parameter> to 1.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>ntile</primary>
</indexterm>
<function>ntile</function> ( <parameter>num_buckets</parameter> <type>integer</type> )
<returnvalue>integer</returnvalue>
</para>
<para>
Returns an integer ranging from 1 to the argument value, dividing the
partition as equally as possible.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>lag</primary>
</indexterm>
<function>lag</function> ( <parameter>value</parameter> <type>anycompatible</type>
<optional>, <parameter>offset</parameter> <type>integer</type>
<optional>, <parameter>default</parameter> <type>anycompatible</type> </optional></optional> )
<returnvalue>anycompatible</returnvalue>
</para>
<para>
Returns <parameter>value</parameter> evaluated at
the row that is <parameter>offset</parameter>
rows before the current row within the partition; if there is no such
row, instead returns <parameter>default</parameter>
(which must be of a type compatible with
<parameter>value</parameter>).
Both <parameter>offset</parameter> and
<parameter>default</parameter> are evaluated
with respect to the current row. If omitted,
<parameter>offset</parameter> defaults to 1 and
<parameter>default</parameter> to <literal>NULL</literal>.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>lead</primary>
</indexterm>
<function>lead</function> ( <parameter>value</parameter> <type>anycompatible</type>
<optional>, <parameter>offset</parameter> <type>integer</type>
<optional>, <parameter>default</parameter> <type>anycompatible</type> </optional></optional> )
<returnvalue>anycompatible</returnvalue>
</para>
<para>
Returns <parameter>value</parameter> evaluated at
the row that is <parameter>offset</parameter>
rows after the current row within the partition; if there is no such
row, instead returns <parameter>default</parameter>
(which must be of a type compatible with
<parameter>value</parameter>).
Both <parameter>offset</parameter> and
<parameter>default</parameter> are evaluated
with respect to the current row. If omitted,
<parameter>offset</parameter> defaults to 1 and
<parameter>default</parameter> to <literal>NULL</literal>.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>first_value</primary>
</indexterm>
<function>first_value</function> ( <parameter>value</parameter> <type>anyelement</type> )
<returnvalue>anyelement</returnvalue>
</para>
<para>
Returns <parameter>value</parameter> evaluated
at the row that is the first row of the window frame.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>last_value</primary>
</indexterm>
<function>last_value</function> ( <parameter>value</parameter> <type>anyelement</type> )
<returnvalue>anyelement</returnvalue>
</para>
<para>
Returns <parameter>value</parameter> evaluated
at the row that is the last row of the window frame.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>nth_value</primary>
</indexterm>
<function>nth_value</function> ( <parameter>value</parameter> <type>anyelement</type>, <parameter>n</parameter> <type>integer</type> )
<returnvalue>anyelement</returnvalue>
</para>
<para>
Returns <parameter>value</parameter> evaluated
at the row that is the <parameter>n</parameter>'th
row of the window frame (counting from 1);
returns <literal>NULL</literal> if there is no such row.
</para></entry>
</row>
</tbody>
</tgroup>
</table>
<para>
All of the functions listed in
<xref linkend="functions-window-table"/> depend on the sort ordering
specified by the <literal>ORDER BY</literal> clause of the associated window
definition. Rows that are not distinct when considering only the
<literal>ORDER BY</literal> columns are said to be <firstterm>peers</firstterm>.
The four ranking functions (including <function>cume_dist</function>) are
defined so that they give the same answer for all rows of a peer group.
</para>
<para>
Note that <function>first_value</function>, <function>last_value</function>, and
<function>nth_value</function> consider only the rows within the <quote>window
frame</quote>, which by default contains the rows from the start of the
partition through the last peer of the current row. This is
likely to give unhelpful results for <function>last_value</function> and
sometimes also <function>nth_value</function>. You can redefine the frame by
adding a suitable frame specification (<literal>RANGE</literal>,
<literal>ROWS</literal> or <literal>GROUPS</literal>) to
the <literal>OVER</literal> clause.
See <xref linkend="syntax-window-functions"/> for more information
about frame specifications.
</para>
<para>
When an aggregate function is used as a window function, it aggregates
over the rows within the current row's window frame.
An aggregate used with <literal>ORDER BY</literal> and the default window frame
definition produces a <quote>running sum</quote> type of behavior, which may or
may not be what's wanted. To obtain
aggregation over the whole partition, omit <literal>ORDER BY</literal> or use
<literal>ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING</literal>.
Other frame specifications can be used to obtain other effects.
</para>
<note>
<para>
The SQL standard defines a <literal>RESPECT NULLS</literal> or
<literal>IGNORE NULLS</literal> option for <function>lead</function>, <function>lag</function>,
<function>first_value</function>, <function>last_value</function>, and
<function>nth_value</function>. This is not implemented in
<productname>PostgreSQL</productname>: the behavior is always the
same as the standard's default, namely <literal>RESPECT NULLS</literal>.
Likewise, the standard's <literal>FROM FIRST</literal> or <literal>FROM LAST</literal>
option for <function>nth_value</function> is not implemented: only the
default <literal>FROM FIRST</literal> behavior is supported. (You can achieve
the result of <literal>FROM LAST</literal> by reversing the <literal>ORDER BY</literal>
ordering.)
</para>
</note>
</sect1>
<sect1 id="functions-subquery">
<title>Subquery Expressions</title>
<indexterm>
<primary>EXISTS</primary>
</indexterm>
<indexterm>
<primary>IN</primary>
</indexterm>
<indexterm>
<primary>NOT IN</primary>
</indexterm>
<indexterm>
<primary>ANY</primary>
</indexterm>
<indexterm>
<primary>ALL</primary>
</indexterm>
<indexterm>
<primary>SOME</primary>
</indexterm>
<indexterm>
<primary>subquery</primary>
</indexterm>
<para>
This section describes the <acronym>SQL</acronym>-compliant subquery
expressions available in <productname>PostgreSQL</productname>.
All of the expression forms documented in this section return
Boolean (true/false) results.
</para>
<sect2 id="functions-subquery-exists">
<title><literal>EXISTS</literal></title>
<synopsis>
EXISTS (<replaceable>subquery</replaceable>)
</synopsis>
<para>
The argument of <token>EXISTS</token> is an arbitrary <command>SELECT</command> statement,
or <firstterm>subquery</firstterm>. The
subquery is evaluated to determine whether it returns any rows.
If it returns at least one row, the result of <token>EXISTS</token> is
<quote>true</quote>; if the subquery returns no rows, the result of <token>EXISTS</token>
is <quote>false</quote>.
</para>
<para>
The subquery can refer to variables from the surrounding query,
which will act as constants during any one evaluation of the subquery.
</para>
<para>
The subquery will generally only be executed long enough to determine
whether at least one row is returned, not all the way to completion.
It is unwise to write a subquery that has side effects (such as
calling sequence functions); whether the side effects occur
might be unpredictable.
</para>
<para>
Since the result depends only on whether any rows are returned,
and not on the contents of those rows, the output list of the
subquery is normally unimportant. A common coding convention is
to write all <literal>EXISTS</literal> tests in the form
<literal>EXISTS(SELECT 1 WHERE ...)</literal>. There are exceptions to
this rule however, such as subqueries that use <token>INTERSECT</token>.
</para>
<para>
This simple example is like an inner join on <literal>col2</literal>, but
it produces at most one output row for each <literal>tab1</literal> row,
even if there are several matching <literal>tab2</literal> rows:
<screen>
SELECT col1
FROM tab1
WHERE EXISTS (SELECT 1 FROM tab2 WHERE col2 = tab1.col2);
</screen>
</para>
</sect2>
<sect2 id="functions-subquery-in">
<title><literal>IN</literal></title>
<synopsis>
<replaceable>expression</replaceable> IN (<replaceable>subquery</replaceable>)
</synopsis>
<para>
The right-hand side is a parenthesized
subquery, which must return exactly one column. The left-hand expression
is evaluated and compared to each row of the subquery result.
The result of <token>IN</token> is <quote>true</quote> if any equal subquery row is found.
The result is <quote>false</quote> if no equal row is found (including the
case where the subquery returns no rows).
</para>
<para>
Note that if the left-hand expression yields null, or if there are
no equal right-hand values and at least one right-hand row yields
null, the result of the <token>IN</token> construct will be null, not false.
This is in accordance with SQL's normal rules for Boolean combinations
of null values.
</para>
<para>
As with <token>EXISTS</token>, it's unwise to assume that the subquery will
be evaluated completely.
</para>
<synopsis>
<replaceable>row_constructor</replaceable> IN (<replaceable>subquery</replaceable>)
</synopsis>
<para>
The left-hand side of this form of <token>IN</token> is a row constructor,
as described in <xref linkend="sql-syntax-row-constructors"/>.
The right-hand side is a parenthesized
subquery, which must return exactly as many columns as there are
expressions in the left-hand row. The left-hand expressions are
evaluated and compared row-wise to each row of the subquery result.
The result of <token>IN</token> is <quote>true</quote> if any equal subquery row is found.
The result is <quote>false</quote> if no equal row is found (including the
case where the subquery returns no rows).
</para>
<para>
As usual, null values in the rows are combined per
the normal rules of SQL Boolean expressions. Two rows are considered
equal if all their corresponding members are non-null and equal; the rows
are unequal if any corresponding members are non-null and unequal;
otherwise the result of that row comparison is unknown (null).
If all the per-row results are either unequal or null, with at least one
null, then the result of <token>IN</token> is null.
</para>
</sect2>
<sect2 id="functions-subquery-notin">
<title><literal>NOT IN</literal></title>
<synopsis>
<replaceable>expression</replaceable> NOT IN (<replaceable>subquery</replaceable>)
</synopsis>
<para>
The right-hand side is a parenthesized
subquery, which must return exactly one column. The left-hand expression
is evaluated and compared to each row of the subquery result.
The result of <token>NOT IN</token> is <quote>true</quote> if only unequal subquery rows
are found (including the case where the subquery returns no rows).
The result is <quote>false</quote> if any equal row is found.
</para>
<para>
Note that if the left-hand expression yields null, or if there are
no equal right-hand values and at least one right-hand row yields
null, the result of the <token>NOT IN</token> construct will be null, not true.
This is in accordance with SQL's normal rules for Boolean combinations
of null values.
</para>
<para>
As with <token>EXISTS</token>, it's unwise to assume that the subquery will
be evaluated completely.
</para>
<synopsis>
<replaceable>row_constructor</replaceable> NOT IN (<replaceable>subquery</replaceable>)
</synopsis>
<para>
The left-hand side of this form of <token>NOT IN</token> is a row constructor,
as described in <xref linkend="sql-syntax-row-constructors"/>.
The right-hand side is a parenthesized
subquery, which must return exactly as many columns as there are
expressions in the left-hand row. The left-hand expressions are
evaluated and compared row-wise to each row of the subquery result.
The result of <token>NOT IN</token> is <quote>true</quote> if only unequal subquery rows
are found (including the case where the subquery returns no rows).
The result is <quote>false</quote> if any equal row is found.
</para>
<para>
As usual, null values in the rows are combined per
the normal rules of SQL Boolean expressions. Two rows are considered
equal if all their corresponding members are non-null and equal; the rows
are unequal if any corresponding members are non-null and unequal;
otherwise the result of that row comparison is unknown (null).
If all the per-row results are either unequal or null, with at least one
null, then the result of <token>NOT IN</token> is null.
</para>
</sect2>
<sect2 id="functions-subquery-any-some">
<title><literal>ANY</literal>/<literal>SOME</literal></title>
<synopsis>
<replaceable>expression</replaceable> <replaceable>operator</replaceable> ANY (<replaceable>subquery</replaceable>)
<replaceable>expression</replaceable> <replaceable>operator</replaceable> SOME (<replaceable>subquery</replaceable>)
</synopsis>
<para>
The right-hand side is a parenthesized
subquery, which must return exactly one column. The left-hand expression
is evaluated and compared to each row of the subquery result using the
given <replaceable>operator</replaceable>, which must yield a Boolean
result.
The result of <token>ANY</token> is <quote>true</quote> if any true result is obtained.
The result is <quote>false</quote> if no true result is found (including the
case where the subquery returns no rows).
</para>
<para>
<token>SOME</token> is a synonym for <token>ANY</token>.
<token>IN</token> is equivalent to <literal>= ANY</literal>.
</para>
<para>
Note that if there are no successes and at least one right-hand row yields
null for the operator's result, the result of the <token>ANY</token> construct
will be null, not false.
This is in accordance with SQL's normal rules for Boolean combinations
of null values.
</para>
<para>
As with <token>EXISTS</token>, it's unwise to assume that the subquery will
be evaluated completely.
</para>
<synopsis>
<replaceable>row_constructor</replaceable> <replaceable>operator</replaceable> ANY (<replaceable>subquery</replaceable>)
<replaceable>row_constructor</replaceable> <replaceable>operator</replaceable> SOME (<replaceable>subquery</replaceable>)
</synopsis>
<para>
The left-hand side of this form of <token>ANY</token> is a row constructor,
as described in <xref linkend="sql-syntax-row-constructors"/>.
The right-hand side is a parenthesized
subquery, which must return exactly as many columns as there are
expressions in the left-hand row. The left-hand expressions are
evaluated and compared row-wise to each row of the subquery result,
using the given <replaceable>operator</replaceable>.
The result of <token>ANY</token> is <quote>true</quote> if the comparison
returns true for any subquery row.
The result is <quote>false</quote> if the comparison returns false for every
subquery row (including the case where the subquery returns no
rows).
The result is NULL if no comparison with a subquery row returns true,
and at least one comparison returns NULL.
</para>
<para>
See <xref linkend="row-wise-comparison"/> for details about the meaning
of a row constructor comparison.
</para>
</sect2>
<sect2 id="functions-subquery-all">
<title><literal>ALL</literal></title>
<synopsis>
<replaceable>expression</replaceable> <replaceable>operator</replaceable> ALL (<replaceable>subquery</replaceable>)
</synopsis>
<para>
The right-hand side is a parenthesized
subquery, which must return exactly one column. The left-hand expression
is evaluated and compared to each row of the subquery result using the
given <replaceable>operator</replaceable>, which must yield a Boolean
result.
The result of <token>ALL</token> is <quote>true</quote> if all rows yield true
(including the case where the subquery returns no rows).
The result is <quote>false</quote> if any false result is found.
The result is NULL if no comparison with a subquery row returns false,
and at least one comparison returns NULL.
</para>
<para>
<token>NOT IN</token> is equivalent to <literal><> ALL</literal>.
</para>
<para>
As with <token>EXISTS</token>, it's unwise to assume that the subquery will
be evaluated completely.
</para>
<synopsis>
<replaceable>row_constructor</replaceable> <replaceable>operator</replaceable> ALL (<replaceable>subquery</replaceable>)
</synopsis>
<para>
The left-hand side of this form of <token>ALL</token> is a row constructor,
as described in <xref linkend="sql-syntax-row-constructors"/>.
The right-hand side is a parenthesized
subquery, which must return exactly as many columns as there are
expressions in the left-hand row. The left-hand expressions are
evaluated and compared row-wise to each row of the subquery result,
using the given <replaceable>operator</replaceable>.
The result of <token>ALL</token> is <quote>true</quote> if the comparison
returns true for all subquery rows (including the
case where the subquery returns no rows).
The result is <quote>false</quote> if the comparison returns false for any
subquery row.
The result is NULL if no comparison with a subquery row returns false,
and at least one comparison returns NULL.
</para>
<para>
See <xref linkend="row-wise-comparison"/> for details about the meaning
of a row constructor comparison.
</para>
</sect2>
<sect2>
<title>Single-Row Comparison</title>
<indexterm zone="functions-subquery">
<primary>comparison</primary>
<secondary>subquery result row</secondary>
</indexterm>
<synopsis>
<replaceable>row_constructor</replaceable> <replaceable>operator</replaceable> (<replaceable>subquery</replaceable>)
</synopsis>
<para>
The left-hand side is a row constructor,
as described in <xref linkend="sql-syntax-row-constructors"/>.
The right-hand side is a parenthesized subquery, which must return exactly
as many columns as there are expressions in the left-hand row. Furthermore,
the subquery cannot return more than one row. (If it returns zero rows,
the result is taken to be null.) The left-hand side is evaluated and
compared row-wise to the single subquery result row.
</para>
<para>
See <xref linkend="row-wise-comparison"/> for details about the meaning
of a row constructor comparison.
</para>
</sect2>
</sect1>
<sect1 id="functions-comparisons">
<title>Row and Array Comparisons</title>
<indexterm>
<primary>IN</primary>
</indexterm>
<indexterm>
<primary>NOT IN</primary>
</indexterm>
<indexterm>
<primary>ANY</primary>
</indexterm>
<indexterm>
<primary>ALL</primary>
</indexterm>
<indexterm>
<primary>SOME</primary>
</indexterm>
<indexterm>
<primary>composite type</primary>
<secondary>comparison</secondary>
</indexterm>
<indexterm>
<primary>row-wise comparison</primary>
</indexterm>
<indexterm>
<primary>comparison</primary>
<secondary>composite type</secondary>
</indexterm>
<indexterm>
<primary>comparison</primary>
<secondary>row constructor</secondary>
</indexterm>
<indexterm>
<primary>IS DISTINCT FROM</primary>
</indexterm>
<indexterm>
<primary>IS NOT DISTINCT FROM</primary>
</indexterm>
<para>
This section describes several specialized constructs for making
multiple comparisons between groups of values. These forms are
syntactically related to the subquery forms of the previous section,
but do not involve subqueries.
The forms involving array subexpressions are
<productname>PostgreSQL</productname> extensions; the rest are
<acronym>SQL</acronym>-compliant.
All of the expression forms documented in this section return
Boolean (true/false) results.
</para>
<sect2 id="functions-comparisons-in-scalar">
<title><literal>IN</literal></title>
<synopsis>
<replaceable>expression</replaceable> IN (<replaceable>value</replaceable> <optional>, ...</optional>)
</synopsis>
<para>
The right-hand side is a parenthesized list
of scalar expressions. The result is <quote>true</quote> if the left-hand expression's
result is equal to any of the right-hand expressions. This is a shorthand
notation for
<synopsis>
<replaceable>expression</replaceable> = <replaceable>value1</replaceable>
OR
<replaceable>expression</replaceable> = <replaceable>value2</replaceable>
OR
...
</synopsis>
</para>
<para>
Note that if the left-hand expression yields null, or if there are
no equal right-hand values and at least one right-hand expression yields
null, the result of the <token>IN</token> construct will be null, not false.
This is in accordance with SQL's normal rules for Boolean combinations
of null values.
</para>
</sect2>
<sect2>
<title><literal>NOT IN</literal></title>
<synopsis>
<replaceable>expression</replaceable> NOT IN (<replaceable>value</replaceable> <optional>, ...</optional>)
</synopsis>
<para>
The right-hand side is a parenthesized list
of scalar expressions. The result is <quote>true</quote> if the left-hand expression's
result is unequal to all of the right-hand expressions. This is a shorthand
notation for
<synopsis>
<replaceable>expression</replaceable> <> <replaceable>value1</replaceable>
AND
<replaceable>expression</replaceable> <> <replaceable>value2</replaceable>
AND
...
</synopsis>
</para>
<para>
Note that if the left-hand expression yields null, or if there are
no equal right-hand values and at least one right-hand expression yields
null, the result of the <token>NOT IN</token> construct will be null, not true
as one might naively expect.
This is in accordance with SQL's normal rules for Boolean combinations
of null values.
</para>
<tip>
<para>
<literal>x NOT IN y</literal> is equivalent to <literal>NOT (x IN y)</literal> in all
cases. However, null values are much more likely to trip up the novice when
working with <token>NOT IN</token> than when working with <token>IN</token>.
It is best to express your condition positively if possible.
</para>
</tip>
</sect2>
<sect2>
<title><literal>ANY</literal>/<literal>SOME</literal> (array)</title>
<synopsis>
<replaceable>expression</replaceable> <replaceable>operator</replaceable> ANY (<replaceable>array expression</replaceable>)
<replaceable>expression</replaceable> <replaceable>operator</replaceable> SOME (<replaceable>array expression</replaceable>)
</synopsis>
<para>
The right-hand side is a parenthesized expression, which must yield an
array value.
The left-hand expression
is evaluated and compared to each element of the array using the
given <replaceable>operator</replaceable>, which must yield a Boolean
result.
The result of <token>ANY</token> is <quote>true</quote> if any true result is obtained.
The result is <quote>false</quote> if no true result is found (including the
case where the array has zero elements).
</para>
<para>
If the array expression yields a null array, the result of
<token>ANY</token> will be null. If the left-hand expression yields null,
the result of <token>ANY</token> is ordinarily null (though a non-strict
comparison operator could possibly yield a different result).
Also, if the right-hand array contains any null elements and no true
comparison result is obtained, the result of <token>ANY</token>
will be null, not false (again, assuming a strict comparison operator).
This is in accordance with SQL's normal rules for Boolean combinations
of null values.
</para>
<para>
<token>SOME</token> is a synonym for <token>ANY</token>.
</para>
</sect2>
<sect2>
<title><literal>ALL</literal> (array)</title>
<synopsis>
<replaceable>expression</replaceable> <replaceable>operator</replaceable> ALL (<replaceable>array expression</replaceable>)
</synopsis>
<para>
The right-hand side is a parenthesized expression, which must yield an
array value.
The left-hand expression
is evaluated and compared to each element of the array using the
given <replaceable>operator</replaceable>, which must yield a Boolean
result.
The result of <token>ALL</token> is <quote>true</quote> if all comparisons yield true
(including the case where the array has zero elements).
The result is <quote>false</quote> if any false result is found.
</para>
<para>
If the array expression yields a null array, the result of
<token>ALL</token> will be null. If the left-hand expression yields null,
the result of <token>ALL</token> is ordinarily null (though a non-strict
comparison operator could possibly yield a different result).
Also, if the right-hand array contains any null elements and no false
comparison result is obtained, the result of <token>ALL</token>
will be null, not true (again, assuming a strict comparison operator).
This is in accordance with SQL's normal rules for Boolean combinations
of null values.
</para>
</sect2>
<sect2 id="row-wise-comparison">
<title>Row Constructor Comparison</title>
<synopsis>
<replaceable>row_constructor</replaceable> <replaceable>operator</replaceable> <replaceable>row_constructor</replaceable>
</synopsis>
<para>
Each side is a row constructor,
as described in <xref linkend="sql-syntax-row-constructors"/>.
The two row values must have the same number of fields.
Each side is evaluated and they are compared row-wise. Row constructor
comparisons are allowed when the <replaceable>operator</replaceable> is
<literal>=</literal>,
<literal><></literal>,
<literal><</literal>,
<literal><=</literal>,
<literal>></literal> or
<literal>>=</literal>.
Every row element must be of a type which has a default B-tree operator
class or the attempted comparison may generate an error.
</para>
<note>
<para>
Errors related to the number or types of elements might not occur if
the comparison is resolved using earlier columns.
</para>
</note>
<para>
The <literal>=</literal> and <literal><></literal> cases work slightly differently
from the others. Two rows are considered
equal if all their corresponding members are non-null and equal; the rows
are unequal if any corresponding members are non-null and unequal;
otherwise the result of the row comparison is unknown (null).
</para>
<para>
For the <literal><</literal>, <literal><=</literal>, <literal>></literal> and
<literal>>=</literal> cases, the row elements are compared left-to-right,
stopping as soon as an unequal or null pair of elements is found.
If either of this pair of elements is null, the result of the
row comparison is unknown (null); otherwise comparison of this pair
of elements determines the result. For example,
<literal>ROW(1,2,NULL) < ROW(1,3,0)</literal>
yields true, not null, because the third pair of elements are not
considered.
</para>
<note>
<para>
Prior to <productname>PostgreSQL</productname> 8.2, the
<literal><</literal>, <literal><=</literal>, <literal>></literal> and <literal>>=</literal>
cases were not handled per SQL specification. A comparison like
<literal>ROW(a,b) < ROW(c,d)</literal>
was implemented as
<literal>a < c AND b < d</literal>
whereas the correct behavior is equivalent to
<literal>a < c OR (a = c AND b < d)</literal>.
</para>
</note>
<synopsis>
<replaceable>row_constructor</replaceable> IS DISTINCT FROM <replaceable>row_constructor</replaceable>
</synopsis>
<para>
This construct is similar to a <literal><></literal> row comparison,
but it does not yield null for null inputs. Instead, any null value is
considered unequal to (distinct from) any non-null value, and any two
nulls are considered equal (not distinct). Thus the result will
either be true or false, never null.
</para>
<synopsis>
<replaceable>row_constructor</replaceable> IS NOT DISTINCT FROM <replaceable>row_constructor</replaceable>
</synopsis>
<para>
This construct is similar to a <literal>=</literal> row comparison,
but it does not yield null for null inputs. Instead, any null value is
considered unequal to (distinct from) any non-null value, and any two
nulls are considered equal (not distinct). Thus the result will always
be either true or false, never null.
</para>
</sect2>
<sect2 id="composite-type-comparison">
<title>Composite Type Comparison</title>
<synopsis>
<replaceable>record</replaceable> <replaceable>operator</replaceable> <replaceable>record</replaceable>
</synopsis>
<para>
The SQL specification requires row-wise comparison to return NULL if the
result depends on comparing two NULL values or a NULL and a non-NULL.
<productname>PostgreSQL</productname> does this only when comparing the
results of two row constructors (as in
<xref linkend="row-wise-comparison"/>) or comparing a row constructor
to the output of a subquery (as in <xref linkend="functions-subquery"/>).
In other contexts where two composite-type values are compared, two
NULL field values are considered equal, and a NULL is considered larger
than a non-NULL. This is necessary in order to have consistent sorting
and indexing behavior for composite types.
</para>
<para>
Each side is evaluated and they are compared row-wise. Composite type
comparisons are allowed when the <replaceable>operator</replaceable> is
<literal>=</literal>,
<literal><></literal>,
<literal><</literal>,
<literal><=</literal>,
<literal>></literal> or
<literal>>=</literal>,
or has semantics similar to one of these. (To be specific, an operator
can be a row comparison operator if it is a member of a B-tree operator
class, or is the negator of the <literal>=</literal> member of a B-tree operator
class.) The default behavior of the above operators is the same as for
<literal>IS [ NOT ] DISTINCT FROM</literal> for row constructors (see
<xref linkend="row-wise-comparison"/>).
</para>
<para>
To support matching of rows which include elements without a default
B-tree operator class, the following operators are defined for composite
type comparison:
<literal>*=</literal>,
<literal>*<></literal>,
<literal>*<</literal>,
<literal>*<=</literal>,
<literal>*></literal>, and
<literal>*>=</literal>.
These operators compare the internal binary representation of the two
rows. Two rows might have a different binary representation even
though comparisons of the two rows with the equality operator is true.
The ordering of rows under these comparison operators is deterministic
but not otherwise meaningful. These operators are used internally
for materialized views and might be useful for other specialized
purposes such as replication and B-Tree deduplication (see <xref
linkend="btree-deduplication"/>). They are not intended to be
generally useful for writing queries, though.
</para>
</sect2>
</sect1>
<sect1 id="functions-srf">
<title>Set Returning Functions</title>
<indexterm zone="functions-srf">
<primary>set returning functions</primary>
<secondary>functions</secondary>
</indexterm>
<para>
This section describes functions that possibly return more than one row.
The most widely used functions in this class are series generating
functions, as detailed in <xref linkend="functions-srf-series"/> and
<xref linkend="functions-srf-subscripts"/>. Other, more specialized
set-returning functions are described elsewhere in this manual.
See <xref linkend="queries-tablefunctions"/> for ways to combine multiple
set-returning functions.
</para>
<table id="functions-srf-series">
<title>Series Generating Functions</title>
<tgroup cols="1">
<thead>
<row>
<entry role="func_table_entry"><para role="func_signature">
Function
</para>
<para>
Description
</para></entry>
</row>
</thead>
<tbody>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>generate_series</primary>
</indexterm>
<function>generate_series</function> ( <parameter>start</parameter> <type>integer</type>, <parameter>stop</parameter> <type>integer</type> <optional>, <parameter>step</parameter> <type>integer</type> </optional> )
<returnvalue>setof integer</returnvalue>
</para>
<para role="func_signature">
<function>generate_series</function> ( <parameter>start</parameter> <type>bigint</type>, <parameter>stop</parameter> <type>bigint</type> <optional>, <parameter>step</parameter> <type>bigint</type> </optional> )
<returnvalue>setof bigint</returnvalue>
</para>
<para role="func_signature">
<function>generate_series</function> ( <parameter>start</parameter> <type>numeric</type>, <parameter>stop</parameter> <type>numeric</type> <optional>, <parameter>step</parameter> <type>numeric</type> </optional> )
<returnvalue>setof numeric</returnvalue>
</para>
<para>
Generates a series of values from <parameter>start</parameter>
to <parameter>stop</parameter>, with a step size
of <parameter>step</parameter>. <parameter>step</parameter>
defaults to 1.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<function>generate_series</function> ( <parameter>start</parameter> <type>timestamp</type>, <parameter>stop</parameter> <type>timestamp</type>, <parameter>step</parameter> <type>interval</type> )
<returnvalue>setof timestamp</returnvalue>
</para>
<para role="func_signature">
<function>generate_series</function> ( <parameter>start</parameter> <type>timestamp with time zone</type>, <parameter>stop</parameter> <type>timestamp with time zone</type>, <parameter>step</parameter> <type>interval</type> )
<returnvalue>setof timestamp with time zone</returnvalue>
</para>
<para>
Generates a series of values from <parameter>start</parameter>
to <parameter>stop</parameter>, with a step size
of <parameter>step</parameter>.
</para></entry>
</row>
</tbody>
</tgroup>
</table>
<para>
When <parameter>step</parameter> is positive, zero rows are returned if
<parameter>start</parameter> is greater than <parameter>stop</parameter>.
Conversely, when <parameter>step</parameter> is negative, zero rows are
returned if <parameter>start</parameter> is less than <parameter>stop</parameter>.
Zero rows are also returned if any input is <literal>NULL</literal>.
It is an error
for <parameter>step</parameter> to be zero. Some examples follow:
<programlisting>
SELECT * FROM generate_series(2,4);
generate_series
-----------------
2
3
4
(3 rows)
SELECT * FROM generate_series(5,1,-2);
generate_series
-----------------
5
3
1
(3 rows)
SELECT * FROM generate_series(4,3);
generate_series
-----------------
(0 rows)
SELECT generate_series(1.1, 4, 1.3);
generate_series
-----------------
1.1
2.4
3.7
(3 rows)
-- this example relies on the date-plus-integer operator:
SELECT current_date + s.a AS dates FROM generate_series(0,14,7) AS s(a);
dates
------------
2004-02-05
2004-02-12
2004-02-19
(3 rows)
SELECT * FROM generate_series('2008-03-01 00:00'::timestamp,
'2008-03-04 12:00', '10 hours');
generate_series
---------------------
2008-03-01 00:00:00
2008-03-01 10:00:00
2008-03-01 20:00:00
2008-03-02 06:00:00
2008-03-02 16:00:00
2008-03-03 02:00:00
2008-03-03 12:00:00
2008-03-03 22:00:00
2008-03-04 08:00:00
(9 rows)
</programlisting>
</para>
<table id="functions-srf-subscripts">
<title>Subscript Generating Functions</title>
<tgroup cols="1">
<thead>
<row>
<entry role="func_table_entry"><para role="func_signature">
Function
</para>
<para>
Description
</para></entry>
</row>
</thead>
<tbody>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>generate_subscripts</primary>
</indexterm>
<function>generate_subscripts</function> ( <parameter>array</parameter> <type>anyarray</type>, <parameter>dim</parameter> <type>integer</type> )
<returnvalue>setof integer</returnvalue>
</para>
<para>
Generates a series comprising the valid subscripts of
the <parameter>dim</parameter>'th dimension of the given array.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<function>generate_subscripts</function> ( <parameter>array</parameter> <type>anyarray</type>, <parameter>dim</parameter> <type>integer</type>, <parameter>reverse</parameter> <type>boolean</type> )
<returnvalue>setof integer</returnvalue>
</para>
<para>
Generates a series comprising the valid subscripts of
the <parameter>dim</parameter>'th dimension of the given array.
When <parameter>reverse</parameter> is true, returns the series in
reverse order.
</para></entry>
</row>
</tbody>
</tgroup>
</table>
<para>
<function>generate_subscripts</function> is a convenience function that generates
the set of valid subscripts for the specified dimension of the given
array.
Zero rows are returned for arrays that do not have the requested dimension,
or if any input is <literal>NULL</literal>.
Some examples follow:
<programlisting>
-- basic usage:
SELECT generate_subscripts('{NULL,1,NULL,2}'::int[], 1) AS s;
s
---
1
2
3
4
(4 rows)
-- presenting an array, the subscript and the subscripted
-- value requires a subquery:
SELECT * FROM arrays;
a
--------------------
{-1,-2}
{100,200,300}
(2 rows)
SELECT a AS array, s AS subscript, a[s] AS value
FROM (SELECT generate_subscripts(a, 1) AS s, a FROM arrays) foo;
array | subscript | value
---------------+-----------+-------
{-1,-2} | 1 | -1
{-1,-2} | 2 | -2
{100,200,300} | 1 | 100
{100,200,300} | 2 | 200
{100,200,300} | 3 | 300
(5 rows)
-- unnest a 2D array:
CREATE OR REPLACE FUNCTION unnest2(anyarray)
RETURNS SETOF anyelement AS $$
select $1[i][j]
from generate_subscripts($1,1) g1(i),
generate_subscripts($1,2) g2(j);
$$ LANGUAGE sql IMMUTABLE;
CREATE FUNCTION
SELECT * FROM unnest2(ARRAY[[1,2],[3,4]]);
unnest2
---------
1
2
3
4
(4 rows)
</programlisting>
</para>
<indexterm>
<primary>ordinality</primary>
</indexterm>
<para>
When a function in the <literal>FROM</literal> clause is suffixed
by <literal>WITH ORDINALITY</literal>, a <type>bigint</type> column is
appended to the function's output column(s), which starts from 1 and
increments by 1 for each row of the function's output.
This is most useful in the case of set returning
functions such as <function>unnest()</function>.
<programlisting>
-- set returning function WITH ORDINALITY:
SELECT * FROM pg_ls_dir('.') WITH ORDINALITY AS t(ls,n);
ls | n
-----------------+----
pg_serial | 1
pg_twophase | 2
postmaster.opts | 3
pg_notify | 4
postgresql.conf | 5
pg_tblspc | 6
logfile | 7
base | 8
postmaster.pid | 9
pg_ident.conf | 10
global | 11
pg_xact | 12
pg_snapshots | 13
pg_multixact | 14
PG_VERSION | 15
pg_wal | 16
pg_hba.conf | 17
pg_stat_tmp | 18
pg_subtrans | 19
(19 rows)
</programlisting>
</para>
</sect1>
<sect1 id="functions-info">
<title>System Information Functions and Operators</title>
<para>
<xref linkend="functions-info-session-table"/> shows several
functions that extract session and system information.
</para>
<para>
In addition to the functions listed in this section, there are a number of
functions related to the statistics system that also provide system
information. See <xref linkend="monitoring-stats-views"/> for more
information.
</para>
<table id="functions-info-session-table">
<title>Session Information Functions</title>
<tgroup cols="1">
<thead>
<row>
<entry role="func_table_entry"><para role="func_signature">
Function
</para>
<para>
Description
</para></entry>
</row>
</thead>
<tbody>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>current_catalog</primary>
</indexterm>
<function>current_catalog</function>
<returnvalue>name</returnvalue>
</para>
<para role="func_signature">
<indexterm>
<primary>current_database</primary>
</indexterm>
<function>current_database</function> ()
<returnvalue>name</returnvalue>
</para>
<para>
Returns the name of the current database. (Databases are
called <quote>catalogs</quote> in the SQL standard,
so <function>current_catalog</function> is the standard's
spelling.)
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>current_query</primary>
</indexterm>
<function>current_query</function> ()
<returnvalue>text</returnvalue>
</para>
<para>
Returns the text of the currently executing query, as submitted
by the client (which might contain more than one statement).
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>current_role</primary>
</indexterm>
<function>current_role</function>
<returnvalue>name</returnvalue>
</para>
<para>
This is equivalent to <function>current_user</function>.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>current_schema</primary>
</indexterm>
<indexterm>
<primary>schema</primary>
<secondary>current</secondary>
</indexterm>
<function>current_schema</function>
<returnvalue>name</returnvalue>
</para>
<para role="func_signature">
<function>current_schema</function> ()
<returnvalue>name</returnvalue>
</para>
<para>
Returns the name of the schema that is first in the search path (or a
null value if the search path is empty). This is the schema that will
be used for any tables or other named objects that are created without
specifying a target schema.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>current_schemas</primary>
</indexterm>
<indexterm>
<primary>search path</primary>
<secondary>current</secondary>
</indexterm>
<function>current_schemas</function> ( <parameter>include_implicit</parameter> <type>boolean</type> )
<returnvalue>name[]</returnvalue>
</para>
<para>
Returns an array of the names of all schemas presently in the
effective search path, in their priority order. (Items in the current
<xref linkend="guc-search-path"/> setting that do not correspond to
existing, searchable schemas are omitted.) If the Boolean argument
is <literal>true</literal>, then implicitly-searched system schemas
such as <literal>pg_catalog</literal> are included in the result.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>current_user</primary>
</indexterm>
<indexterm>
<primary>user</primary>
<secondary>current</secondary>
</indexterm>
<function>current_user</function>
<returnvalue>name</returnvalue>
</para>
<para>
Returns the user name of the current execution context.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>inet_client_addr</primary>
</indexterm>
<function>inet_client_addr</function> ()
<returnvalue>inet</returnvalue>
</para>
<para>
Returns the IP address of the current client,
or <literal>NULL</literal> if the current connection is via a
Unix-domain socket.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>inet_client_port</primary>
</indexterm>
<function>inet_client_port</function> ()
<returnvalue>integer</returnvalue>
</para>
<para>
Returns the IP port number of the current client,
or <literal>NULL</literal> if the current connection is via a
Unix-domain socket.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>inet_server_addr</primary>
</indexterm>
<function>inet_server_addr</function> ()
<returnvalue>inet</returnvalue>
</para>
<para>
Returns the IP address on which the server accepted the current
connection,
or <literal>NULL</literal> if the current connection is via a
Unix-domain socket.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>inet_server_port</primary>
</indexterm>
<function>inet_server_port</function> ()
<returnvalue>integer</returnvalue>
</para>
<para>
Returns the IP port number on which the server accepted the current
connection,
or <literal>NULL</literal> if the current connection is via a
Unix-domain socket.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_backend_pid</primary>
</indexterm>
<function>pg_backend_pid</function> ()
<returnvalue>integer</returnvalue>
</para>
<para>
Returns the process ID of the server process attached to the current
session.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_blocking_pids</primary>
</indexterm>
<function>pg_blocking_pids</function> ( <type>integer</type> )
<returnvalue>integer[]</returnvalue>
</para>
<para>
Returns an array of the process ID(s) of the sessions that are
blocking the server process with the specified process ID from
acquiring a lock, or an empty array if there is no such server process
or it is not blocked.
</para>
<para>
One server process blocks another if it either holds a lock that
conflicts with the blocked process's lock request (hard block), or is
waiting for a lock that would conflict with the blocked process's lock
request and is ahead of it in the wait queue (soft block). When using
parallel queries the result always lists client-visible process IDs
(that is, <function>pg_backend_pid</function> results) even if the
actual lock is held or awaited by a child worker process. As a result
of that, there may be duplicated PIDs in the result. Also note that
when a prepared transaction holds a conflicting lock, it will be
represented by a zero process ID.
</para>
<para>
Frequent calls to this function could have some impact on database
performance, because it needs exclusive access to the lock manager's
shared state for a short time.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_conf_load_time</primary>
</indexterm>
<function>pg_conf_load_time</function> ()
<returnvalue>timestamp with time zone</returnvalue>
</para>
<para>
Returns the time when the server configuration files were last loaded.
If the current session was alive at the time, this will be the time
when the session itself re-read the configuration files (so the
reading will vary a little in different sessions). Otherwise it is
the time when the postmaster process re-read the configuration files.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_current_logfile</primary>
</indexterm>
<indexterm>
<primary>Logging</primary>
<secondary>pg_current_logfile function</secondary>
</indexterm>
<indexterm>
<primary>current_logfiles</primary>
<secondary>and the pg_current_logfile function</secondary>
</indexterm>
<indexterm>
<primary>Logging</primary>
<secondary>current_logfiles file and the pg_current_logfile
function</secondary>
</indexterm>
<function>pg_current_logfile</function> ( <optional> <type>text</type> </optional> )
<returnvalue>text</returnvalue>
</para>
<para>
Returns the path name of the log file currently in use by the logging
collector. The path includes the <xref linkend="guc-log-directory"/>
directory and the individual log file name. The result
is <literal>NULL</literal> if the logging collector is disabled.
When multiple log files exist, each in a different
format, <function>pg_current_logfile</function> without an argument
returns the path of the file having the first format found in the
ordered list: <literal>stderr</literal>,
<literal>csvlog</literal>. <literal>NULL</literal> is returned
if no log file has any of these formats.
To request information about a specific log file format, supply
either <literal>csvlog</literal> or <literal>stderr</literal> as the
value of the optional parameter. The result is <literal>NULL</literal>
if the log format requested is not configured in
<xref linkend="guc-log-destination"/>.
The result reflects the contents of
the <filename>current_logfiles</filename> file.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_my_temp_schema</primary>
</indexterm>
<function>pg_my_temp_schema</function> ()
<returnvalue>oid</returnvalue>
</para>
<para>
Returns the OID of the current session's temporary schema, or zero if
it has none (because it has not created any temporary tables).
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_is_other_temp_schema</primary>
</indexterm>
<function>pg_is_other_temp_schema</function> ( <type>oid</type> )
<returnvalue>boolean</returnvalue>
</para>
<para>
Returns true if the given OID is the OID of another session's
temporary schema. (This can be useful, for example, to exclude other
sessions' temporary tables from a catalog display.)
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_jit_available</primary>
</indexterm>
<function>pg_jit_available</function> ()
<returnvalue>boolean</returnvalue>
</para>
<para>
Returns true if a <acronym>JIT</acronym> compiler extension is
available (see <xref linkend="jit"/>) and the
<xref linkend="guc-jit"/> configuration parameter is set to
<literal>on</literal>.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_listening_channels</primary>
</indexterm>
<function>pg_listening_channels</function> ()
<returnvalue>setof text</returnvalue>
</para>
<para>
Returns the set of names of asynchronous notification channels that
the current session is listening to.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_notification_queue_usage</primary>
</indexterm>
<function>pg_notification_queue_usage</function> ()
<returnvalue>double precision</returnvalue>
</para>
<para>
Returns the fraction (0–1) of the asynchronous notification
queue's maximum size that is currently occupied by notifications that
are waiting to be processed.
See <xref linkend="sql-listen"/> and <xref linkend="sql-notify"/>
for more information.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_postmaster_start_time</primary>
</indexterm>
<function>pg_postmaster_start_time</function> ()
<returnvalue>timestamp with time zone</returnvalue>
</para>
<para>
Returns the time when the server started.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_safe_snapshot_blocking_pids</primary>
</indexterm>
<function>pg_safe_snapshot_blocking_pids</function> ( <type>integer</type> )
<returnvalue>integer[]</returnvalue>
</para>
<para>
Returns an array of the process ID(s) of the sessions that are blocking
the server process with the specified process ID from acquiring a safe
snapshot, or an empty array if there is no such server process or it
is not blocked.
</para>
<para>
A session running a <literal>SERIALIZABLE</literal> transaction blocks
a <literal>SERIALIZABLE READ ONLY DEFERRABLE</literal> transaction
from acquiring a snapshot until the latter determines that it is safe
to avoid taking any predicate locks. See
<xref linkend="xact-serializable"/> for more information about
serializable and deferrable transactions.
</para>
<para>
Frequent calls to this function could have some impact on database
performance, because it needs access to the predicate lock manager's
shared state for a short time.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_trigger_depth</primary>
</indexterm>
<function>pg_trigger_depth</function> ()
<returnvalue>integer</returnvalue>
</para>
<para>
Returns the current nesting level
of <productname>PostgreSQL</productname> triggers (0 if not called,
directly or indirectly, from inside a trigger).
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>session_user</primary>
</indexterm>
<function>session_user</function>
<returnvalue>name</returnvalue>
</para>
<para>
Returns the session user's name.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>user</primary>
</indexterm>
<function>user</function>
<returnvalue>name</returnvalue>
</para>
<para>
This is equivalent to <function>current_user</function>.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>version</primary>
</indexterm>
<function>version</function> ()
<returnvalue>text</returnvalue>
</para>
<para>
Returns a string describing the <productname>PostgreSQL</productname>
server's version. You can also get this information from
<xref linkend="guc-server-version"/>, or for a machine-readable
version use <xref linkend="guc-server-version-num"/>. Software
developers should use <varname>server_version_num</varname> (available
since 8.2) or <xref linkend="libpq-PQserverVersion"/> instead of
parsing the text version.
</para></entry>
</row>
</tbody>
</tgroup>
</table>
<note>
<para>
<function>current_catalog</function>,
<function>current_role</function>,
<function>current_schema</function>,
<function>current_user</function>,
<function>session_user</function>,
and <function>user</function> have special syntactic status
in <acronym>SQL</acronym>: they must be called without trailing
parentheses. In PostgreSQL, parentheses can optionally be used with
<function>current_schema</function>, but not with the others.
</para>
</note>
<para>
The <function>session_user</function> is normally the user who initiated
the current database connection; but superusers can change this setting
with <xref linkend="sql-set-session-authorization"/>.
The <function>current_user</function> is the user identifier
that is applicable for permission checking. Normally it is equal
to the session user, but it can be changed with
<xref linkend="sql-set-role"/>.
It also changes during the execution of
functions with the attribute <literal>SECURITY DEFINER</literal>.
In Unix parlance, the session user is the <quote>real user</quote> and
the current user is the <quote>effective user</quote>.
<function>current_role</function> and <function>user</function> are
synonyms for <function>current_user</function>. (The SQL standard draws
a distinction between <function>current_role</function>
and <function>current_user</function>, but <productname>PostgreSQL</productname>
does not, since it unifies users and roles into a single kind of entity.)
</para>
<indexterm>
<primary>privilege</primary>
<secondary>querying</secondary>
</indexterm>
<para>
<xref linkend="functions-info-access-table"/> lists functions that
allow querying object access privileges programmatically.
(See <xref linkend="ddl-priv"/> for more information about
privileges.)
In these functions, the user whose privileges are being inquired about
can be specified by name or by OID
(<structname>pg_authid</structname>.<structfield>oid</structfield>), or if
the name is given as <literal>public</literal> then the privileges of the
PUBLIC pseudo-role are checked. Also, the <parameter>user</parameter>
argument can be omitted entirely, in which case
the <function>current_user</function> is assumed.
The object that is being inquired about can be specified either by name or
by OID, too. When specifying by name, a schema name can be included if
relevant.
The access privilege of interest is specified by a text string, which must
evaluate to one of the appropriate privilege keywords for the object's type
(e.g., <literal>SELECT</literal>). Optionally, <literal>WITH GRANT
OPTION</literal> can be added to a privilege type to test whether the
privilege is held with grant option. Also, multiple privilege types can be
listed separated by commas, in which case the result will be true if any of
the listed privileges is held. (Case of the privilege string is not
significant, and extra whitespace is allowed between but not within
privilege names.)
Some examples:
<programlisting>
SELECT has_table_privilege('myschema.mytable', 'select');
SELECT has_table_privilege('joe', 'mytable', 'INSERT, SELECT WITH GRANT OPTION');
</programlisting>
</para>
<table id="functions-info-access-table">
<title>Access Privilege Inquiry Functions</title>
<tgroup cols="1">
<thead>
<row>
<entry role="func_table_entry"><para role="func_signature">
Function
</para>
<para>
Description
</para></entry>
</row>
</thead>
<tbody>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>has_any_column_privilege</primary>
</indexterm>
<function>has_any_column_privilege</function> (
<optional> <parameter>user</parameter> <type>name</type> or <type>oid</type>, </optional>
<parameter>table</parameter> <type>text</type> or <type>oid</type>,
<parameter>privilege</parameter> <type>text</type> )
<returnvalue>boolean</returnvalue>
</para>
<para>
Does user have privilege for any column of table?
This succeeds either if the privilege is held for the whole table, or
if there is a column-level grant of the privilege for at least one
column.
Allowable privilege types are
<literal>SELECT</literal>, <literal>INSERT</literal>,
<literal>UPDATE</literal>, and <literal>REFERENCES</literal>.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>has_column_privilege</primary>
</indexterm>
<function>has_column_privilege</function> (
<optional> <parameter>user</parameter> <type>name</type> or <type>oid</type>, </optional>
<parameter>table</parameter> <type>text</type> or <type>oid</type>,
<parameter>column</parameter> <type>text</type> or <type>smallint</type>,
<parameter>privilege</parameter> <type>text</type> )
<returnvalue>boolean</returnvalue>
</para>
<para>
Does user have privilege for the specified table column?
This succeeds either if the privilege is held for the whole table, or
if there is a column-level grant of the privilege for the column.
The column can be specified by name or by attribute number
(<structname>pg_attribute</structname>.<structfield>attnum</structfield>).
Allowable privilege types are
<literal>SELECT</literal>, <literal>INSERT</literal>,
<literal>UPDATE</literal>, and <literal>REFERENCES</literal>.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>has_database_privilege</primary>
</indexterm>
<function>has_database_privilege</function> (
<optional> <parameter>user</parameter> <type>name</type> or <type>oid</type>, </optional>
<parameter>database</parameter> <type>text</type> or <type>oid</type>,
<parameter>privilege</parameter> <type>text</type> )
<returnvalue>boolean</returnvalue>
</para>
<para>
Does user have privilege for database?
Allowable privilege types are
<literal>CREATE</literal>,
<literal>CONNECT</literal>,
<literal>TEMPORARY</literal>, and
<literal>TEMP</literal> (which is equivalent to
<literal>TEMPORARY</literal>).
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>has_foreign_data_wrapper_privilege</primary>
</indexterm>
<function>has_foreign_data_wrapper_privilege</function> (
<optional> <parameter>user</parameter> <type>name</type> or <type>oid</type>, </optional>
<parameter>fdw</parameter> <type>text</type> or <type>oid</type>,
<parameter>privilege</parameter> <type>text</type> )
<returnvalue>boolean</returnvalue>
</para>
<para>
Does user have privilege for foreign-data wrapper?
The only allowable privilege type is <literal>USAGE</literal>.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>has_function_privilege</primary>
</indexterm>
<function>has_function_privilege</function> (
<optional> <parameter>user</parameter> <type>name</type> or <type>oid</type>, </optional>
<parameter>function</parameter> <type>text</type> or <type>oid</type>,
<parameter>privilege</parameter> <type>text</type> )
<returnvalue>boolean</returnvalue>
</para>
<para>
Does user have privilege for function?
The only allowable privilege type is <literal>EXECUTE</literal>.
</para>
<para>
When specifying a function by name rather than by OID, the allowed
input is the same as for the <type>regprocedure</type> data type (see
<xref linkend="datatype-oid"/>).
An example is:
<programlisting>
SELECT has_function_privilege('joeuser', 'myfunc(int, text)', 'execute');
</programlisting>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>has_language_privilege</primary>
</indexterm>
<function>has_language_privilege</function> (
<optional> <parameter>user</parameter> <type>name</type> or <type>oid</type>, </optional>
<parameter>language</parameter> <type>text</type> or <type>oid</type>,
<parameter>privilege</parameter> <type>text</type> )
<returnvalue>boolean</returnvalue>
</para>
<para>
Does user have privilege for language?
The only allowable privilege type is <literal>USAGE</literal>.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>has_schema_privilege</primary>
</indexterm>
<function>has_schema_privilege</function> (
<optional> <parameter>user</parameter> <type>name</type> or <type>oid</type>, </optional>
<parameter>schema</parameter> <type>text</type> or <type>oid</type>,
<parameter>privilege</parameter> <type>text</type> )
<returnvalue>boolean</returnvalue>
</para>
<para>
Does user have privilege for schema?
Allowable privilege types are
<literal>CREATE</literal> and
<literal>USAGE</literal>.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>has_sequence_privilege</primary>
</indexterm>
<function>has_sequence_privilege</function> (
<optional> <parameter>user</parameter> <type>name</type> or <type>oid</type>, </optional>
<parameter>sequence</parameter> <type>text</type> or <type>oid</type>,
<parameter>privilege</parameter> <type>text</type> )
<returnvalue>boolean</returnvalue>
</para>
<para>
Does user have privilege for sequence?
Allowable privilege types are
<literal>USAGE</literal>,
<literal>SELECT</literal>, and
<literal>UPDATE</literal>.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>has_server_privilege</primary>
</indexterm>
<function>has_server_privilege</function> (
<optional> <parameter>user</parameter> <type>name</type> or <type>oid</type>, </optional>
<parameter>server</parameter> <type>text</type> or <type>oid</type>,
<parameter>privilege</parameter> <type>text</type> )
<returnvalue>boolean</returnvalue>
</para>
<para>
Does user have privilege for foreign server?
The only allowable privilege type is <literal>USAGE</literal>.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>has_table_privilege</primary>
</indexterm>
<function>has_table_privilege</function> (
<optional> <parameter>user</parameter> <type>name</type> or <type>oid</type>, </optional>
<parameter>table</parameter> <type>text</type> or <type>oid</type>,
<parameter>privilege</parameter> <type>text</type> )
<returnvalue>boolean</returnvalue>
</para>
<para>
Does user have privilege for table?
Allowable privilege types
are <literal>SELECT</literal>, <literal>INSERT</literal>,
<literal>UPDATE</literal>, <literal>DELETE</literal>,
<literal>TRUNCATE</literal>, <literal>REFERENCES</literal>,
and <literal>TRIGGER</literal>.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>has_tablespace_privilege</primary>
</indexterm>
<function>has_tablespace_privilege</function> (
<optional> <parameter>user</parameter> <type>name</type> or <type>oid</type>, </optional>
<parameter>tablespace</parameter> <type>text</type> or <type>oid</type>,
<parameter>privilege</parameter> <type>text</type> )
<returnvalue>boolean</returnvalue>
</para>
<para>
Does user have privilege for tablespace?
The only allowable privilege type is <literal>CREATE</literal>.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>has_type_privilege</primary>
</indexterm>
<function>has_type_privilege</function> (
<optional> <parameter>user</parameter> <type>name</type> or <type>oid</type>, </optional>
<parameter>type</parameter> <type>text</type> or <type>oid</type>,
<parameter>privilege</parameter> <type>text</type> )
<returnvalue>boolean</returnvalue>
</para>
<para>
Does user have privilege for data type?
The only allowable privilege type is <literal>USAGE</literal>.
When specifying a type by name rather than by OID, the allowed input
is the same as for the <type>regtype</type> data type (see
<xref linkend="datatype-oid"/>).
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_has_role</primary>
</indexterm>
<function>pg_has_role</function> (
<optional> <parameter>user</parameter> <type>name</type> or <type>oid</type>, </optional>
<parameter>role</parameter> <type>text</type> or <type>oid</type>,
<parameter>privilege</parameter> <type>text</type> )
<returnvalue>boolean</returnvalue>
</para>
<para>
Does user have privilege for role?
Allowable privilege types are
<literal>MEMBER</literal> and <literal>USAGE</literal>.
<literal>MEMBER</literal> denotes direct or indirect membership in
the role (that is, the right to do <command>SET ROLE</command>), while
<literal>USAGE</literal> denotes whether the privileges of the role
are immediately available without doing <command>SET ROLE</command>.
This function does not allow the special case of
setting <parameter>user</parameter> to <literal>public</literal>,
because the PUBLIC pseudo-role can never be a member of real roles.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>row_security_active</primary>
</indexterm>
<function>row_security_active</function> (
<parameter>table</parameter> <type>text</type> or <type>oid</type> )
<returnvalue>boolean</returnvalue>
</para>
<para>
Is row-level security active for the specified table in the context of
the current user and current environment?
</para></entry>
</row>
</tbody>
</tgroup>
</table>
<para>
<xref linkend="functions-aclitem-op-table"/> shows the operators
available for the <type>aclitem</type> type, which is the catalog
representation of access privileges. See <xref linkend="ddl-priv"/>
for information about how to read access privilege values.
</para>
<table id="functions-aclitem-op-table">
<title><type>aclitem</type> Operators</title>
<tgroup cols="1">
<thead>
<row>
<entry role="func_table_entry"><para role="func_signature">
Operator
</para>
<para>
Description
</para>
<para>
Example(s)
</para></entry>
</row>
</thead>
<tbody>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>aclitemeq</primary>
</indexterm>
<type>aclitem</type> <literal>=</literal> <type>aclitem</type>
<returnvalue>boolean</returnvalue>
</para>
<para>
Are <type>aclitem</type>s equal? (Notice that
type <type>aclitem</type> lacks the usual set of comparison
operators; it has only equality. In turn, <type>aclitem</type>
arrays can only be compared for equality.)
</para>
<para>
<literal>'calvin=r*w/hobbes'::aclitem = 'calvin=r*w*/hobbes'::aclitem</literal>
<returnvalue>f</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>aclcontains</primary>
</indexterm>
<type>aclitem[]</type> <literal>@></literal> <type>aclitem</type>
<returnvalue>boolean</returnvalue>
</para>
<para>
Does array contain the specified privileges? (This is true if there
is an array entry that matches the <type>aclitem</type>'s grantee and
grantor, and has at least the specified set of privileges.)
</para>
<para>
<literal>'{calvin=r*w/hobbes,hobbes=r*w*/postgres}'::aclitem[] @> 'calvin=r*/hobbes'::aclitem</literal>
<returnvalue>t</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<type>aclitem[]</type> <literal>~</literal> <type>aclitem</type>
<returnvalue>boolean</returnvalue>
</para>
<para>
This is a deprecated alias for <literal>@></literal>.
</para>
<para>
<literal>'{calvin=r*w/hobbes,hobbes=r*w*/postgres}'::aclitem[] ~ 'calvin=r*/hobbes'::aclitem</literal>
<returnvalue>t</returnvalue>
</para></entry>
</row>
</tbody>
</tgroup>
</table>
<para>
<xref linkend="functions-aclitem-fn-table"/> shows some additional
functions to manage the <type>aclitem</type> type.
</para>
<table id="functions-aclitem-fn-table">
<title><type>aclitem</type> Functions</title>
<tgroup cols="1">
<thead>
<row>
<entry role="func_table_entry"><para role="func_signature">
Function
</para>
<para>
Description
</para></entry>
</row>
</thead>
<tbody>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>acldefault</primary>
</indexterm>
<function>acldefault</function> (
<parameter>type</parameter> <type>"char"</type>,
<parameter>ownerId</parameter> <type>oid</type> )
<returnvalue>aclitem[]</returnvalue>
</para>
<para>
Constructs an <type>aclitem</type> array holding the default access
privileges for an object of type <parameter>type</parameter> belonging
to the role with OID <parameter>ownerId</parameter>. This represents
the access privileges that will be assumed when an object's ACL entry
is null. (The default access privileges are described in
<xref linkend="ddl-priv"/>.)
The <parameter>type</parameter> parameter must be one of
'c' for <literal>COLUMN</literal>,
'r' for <literal>TABLE</literal> and table-like objects,
's' for <literal>SEQUENCE</literal>,
'd' for <literal>DATABASE</literal>,
'f' for <literal>FUNCTION</literal> or <literal>PROCEDURE</literal>,
'l' for <literal>LANGUAGE</literal>,
'L' for <literal>LARGE OBJECT</literal>,
'n' for <literal>SCHEMA</literal>,
't' for <literal>TABLESPACE</literal>,
'F' for <literal>FOREIGN DATA WRAPPER</literal>,
'S' for <literal>FOREIGN SERVER</literal>,
or
'T' for <literal>TYPE</literal> or <literal>DOMAIN</literal>.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>aclexplode</primary>
</indexterm>
<function>aclexplode</function> ( <type>aclitem[]</type> )
<returnvalue>setof record</returnvalue>
( <parameter>grantor</parameter> <type>oid</type>,
<parameter>grantee</parameter> <type>oid</type>,
<parameter>privilege_type</parameter> <type>text</type>,
<parameter>is_grantable</parameter> <type>boolean</type> )
</para>
<para>
Returns the <type>aclitem</type> array as a set of rows.
If the grantee is the pseudo-role PUBLIC, it is represented by zero in
the <parameter>grantee</parameter> column. Each granted privilege is
represented as <literal>SELECT</literal>, <literal>INSERT</literal>,
etc. Note that each privilege is broken out as a separate row, so
only one keyword appears in the <parameter>privilege_type</parameter>
column.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>makeaclitem</primary>
</indexterm>
<function>makeaclitem</function> (
<parameter>grantee</parameter> <type>oid</type>,
<parameter>grantor</parameter> <type>oid</type>,
<parameter>privileges</parameter> <type>text</type>,
<parameter>is_grantable</parameter> <type>boolean</type> )
<returnvalue>aclitem</returnvalue>
</para>
<para>
Constructs an <type>aclitem</type> with the given properties.
</para></entry>
</row>
</tbody>
</tgroup>
</table>
<para>
<xref linkend="functions-info-schema-table"/> shows functions that
determine whether a certain object is <firstterm>visible</firstterm> in the
current schema search path.
For example, a table is said to be visible if its
containing schema is in the search path and no table of the same
name appears earlier in the search path. This is equivalent to the
statement that the table can be referenced by name without explicit
schema qualification. Thus, to list the names of all visible tables:
<programlisting>
SELECT relname FROM pg_class WHERE pg_table_is_visible(oid);
</programlisting>
For functions and operators, an object in the search path is said to be
visible if there is no object of the same name <emphasis>and argument data
type(s)</emphasis> earlier in the path. For operator classes and families,
both the name and the associated index access method are considered.
</para>
<indexterm>
<primary>search path</primary>
<secondary>object visibility</secondary>
</indexterm>
<table id="functions-info-schema-table">
<title>Schema Visibility Inquiry Functions</title>
<tgroup cols="1">
<thead>
<row>
<entry role="func_table_entry"><para role="func_signature">
Function
</para>
<para>
Description
</para></entry>
</row>
</thead>
<tbody>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_collation_is_visible</primary>
</indexterm>
<function>pg_collation_is_visible</function> ( <parameter>collation</parameter> <type>oid</type> )
<returnvalue>boolean</returnvalue>
</para>
<para>
Is collation visible in search path?
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_conversion_is_visible</primary>
</indexterm>
<function>pg_conversion_is_visible</function> ( <parameter>conversion</parameter> <type>oid</type> )
<returnvalue>boolean</returnvalue>
</para>
<para>
Is conversion visible in search path?
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_function_is_visible</primary>
</indexterm>
<function>pg_function_is_visible</function> ( <parameter>function</parameter> <type>oid</type> )
<returnvalue>boolean</returnvalue>
</para>
<para>
Is function visible in search path?
(This also works for procedures and aggregates.)
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_opclass_is_visible</primary>
</indexterm>
<function>pg_opclass_is_visible</function> ( <parameter>opclass</parameter> <type>oid</type> )
<returnvalue>boolean</returnvalue>
</para>
<para>
Is operator class visible in search path?
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_operator_is_visible</primary>
</indexterm>
<function>pg_operator_is_visible</function> ( <parameter>operator</parameter> <type>oid</type> )
<returnvalue>boolean</returnvalue>
</para>
<para>
Is operator visible in search path?
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_opfamily_is_visible</primary>
</indexterm>
<function>pg_opfamily_is_visible</function> ( <parameter>opclass</parameter> <type>oid</type> )
<returnvalue>boolean</returnvalue>
</para>
<para>
Is operator family visible in search path?
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_statistics_obj_is_visible</primary>
</indexterm>
<function>pg_statistics_obj_is_visible</function> ( <parameter>stat</parameter> <type>oid</type> )
<returnvalue>boolean</returnvalue>
</para>
<para>
Is statistics object visible in search path?
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_table_is_visible</primary>
</indexterm>
<function>pg_table_is_visible</function> ( <parameter>table</parameter> <type>oid</type> )
<returnvalue>boolean</returnvalue>
</para>
<para>
Is table visible in search path?
(This works for all types of relations, including views, materialized
views, indexes, sequences and foreign tables.)
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_ts_config_is_visible</primary>
</indexterm>
<function>pg_ts_config_is_visible</function> ( <parameter>config</parameter> <type>oid</type> )
<returnvalue>boolean</returnvalue>
</para>
<para>
Is text search configuration visible in search path?
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_ts_dict_is_visible</primary>
</indexterm>
<function>pg_ts_dict_is_visible</function> ( <parameter>dict</parameter> <type>oid</type> )
<returnvalue>boolean</returnvalue>
</para>
<para>
Is text search dictionary visible in search path?
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_ts_parser_is_visible</primary>
</indexterm>
<function>pg_ts_parser_is_visible</function> ( <parameter>parser</parameter> <type>oid</type> )
<returnvalue>boolean</returnvalue>
</para>
<para>
Is text search parser visible in search path?
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_ts_template_is_visible</primary>
</indexterm>
<function>pg_ts_template_is_visible</function> ( <parameter>template</parameter> <type>oid</type> )
<returnvalue>boolean</returnvalue>
</para>
<para>
Is text search template visible in search path?
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_type_is_visible</primary>
</indexterm>
<function>pg_type_is_visible</function> ( <parameter>type</parameter> <type>oid</type> )
<returnvalue>boolean</returnvalue>
</para>
<para>
Is type (or domain) visible in search path?
</para></entry>
</row>
</tbody>
</tgroup>
</table>
<para>
All these functions require object OIDs to identify the object to be
checked. If you want to test an object by name, it is convenient to use
the OID alias types (<type>regclass</type>, <type>regtype</type>,
<type>regprocedure</type>, <type>regoperator</type>, <type>regconfig</type>,
or <type>regdictionary</type>),
for example:
<programlisting>
SELECT pg_type_is_visible('myschema.widget'::regtype);
</programlisting>
Note that it would not make much sense to test a non-schema-qualified
type name in this way — if the name can be recognized at all, it must be visible.
</para>
<para>
<xref linkend="functions-info-catalog-table"/> lists functions that
extract information from the system catalogs.
</para>
<table id="functions-info-catalog-table">
<title>System Catalog Information Functions</title>
<tgroup cols="1">
<thead>
<row>
<entry role="func_table_entry"><para role="func_signature">
Function
</para>
<para>
Description
</para></entry>
</row>
</thead>
<tbody>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>format_type</primary>
</indexterm>
<function>format_type</function> ( <parameter>type</parameter> <type>oid</type>, <parameter>typemod</parameter> <type>integer</type> )
<returnvalue>text</returnvalue>
</para>
<para>
Returns the SQL name for a data type that is identified by its type
OID and possibly a type modifier. Pass NULL for the type modifier if
no specific modifier is known.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_get_catalog_foreign_keys</primary>
</indexterm>
<function>pg_get_catalog_foreign_keys</function> ()
<returnvalue>setof record</returnvalue>
( <parameter>fktable</parameter> <type>regclass</type>,
<parameter>fkcols</parameter> <type>text[]</type>,
<parameter>pktable</parameter> <type>regclass</type>,
<parameter>pkcols</parameter> <type>text[]</type>,
<parameter>is_array</parameter> <type>boolean</type>,
<parameter>is_opt</parameter> <type>boolean</type> )
</para>
<para>
Returns a set of records describing the foreign key relationships
that exist within the <productname>PostgreSQL</productname> system
catalogs.
The <parameter>fktable</parameter> column contains the name of the
referencing catalog, and the <parameter>fkcols</parameter> column
contains the name(s) of the referencing column(s). Similarly,
the <parameter>pktable</parameter> column contains the name of the
referenced catalog, and the <parameter>pkcols</parameter> column
contains the name(s) of the referenced column(s).
If <parameter>is_array</parameter> is true, the last referencing
column is an array, each of whose elements should match some entry
in the referenced catalog.
If <parameter>is_opt</parameter> is true, the referencing column(s)
are allowed to contain zeroes instead of a valid reference.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_get_constraintdef</primary>
</indexterm>
<function>pg_get_constraintdef</function> ( <parameter>constraint</parameter> <type>oid</type> <optional>, <parameter>pretty</parameter> <type>boolean</type> </optional> )
<returnvalue>text</returnvalue>
</para>
<para>
Reconstructs the creating command for a constraint.
(This is a decompiled reconstruction, not the original text
of the command.)
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_get_expr</primary>
</indexterm>
<function>pg_get_expr</function> ( <parameter>expr</parameter> <type>pg_node_tree</type>, <parameter>relation</parameter> <type>oid</type> <optional>, <parameter>pretty</parameter> <type>boolean</type> </optional> )
<returnvalue>text</returnvalue>
</para>
<para>
Decompiles the internal form of an expression stored in the system
catalogs, such as the default value for a column. If the expression
might contain Vars, specify the OID of the relation they refer to as
the second parameter; if no Vars are expected, passing zero is
sufficient.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_get_functiondef</primary>
</indexterm>
<function>pg_get_functiondef</function> ( <parameter>func</parameter> <type>oid</type> )
<returnvalue>text</returnvalue>
</para>
<para>
Reconstructs the creating command for a function or procedure.
(This is a decompiled reconstruction, not the original text
of the command.)
The result is a complete <command>CREATE OR REPLACE FUNCTION</command>
or <command>CREATE OR REPLACE PROCEDURE</command> statement.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_get_function_arguments</primary>
</indexterm>
<function>pg_get_function_arguments</function> ( <parameter>func</parameter> <type>oid</type> )
<returnvalue>text</returnvalue>
</para>
<para>
Reconstructs the argument list of a function or procedure, in the form
it would need to appear in within <command>CREATE FUNCTION</command>
(including default values).
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_get_function_identity_arguments</primary>
</indexterm>
<function>pg_get_function_identity_arguments</function> ( <parameter>func</parameter> <type>oid</type> )
<returnvalue>text</returnvalue>
</para>
<para>
Reconstructs the argument list necessary to identify a function or
procedure, in the form it would need to appear in within commands such
as <command>ALTER FUNCTION</command>. This form omits default values.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_get_function_result</primary>
</indexterm>
<function>pg_get_function_result</function> ( <parameter>func</parameter> <type>oid</type> )
<returnvalue>text</returnvalue>
</para>
<para>
Reconstructs the <literal>RETURNS</literal> clause of a function, in
the form it would need to appear in within <command>CREATE
FUNCTION</command>. Returns <literal>NULL</literal> for a procedure.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_get_indexdef</primary>
</indexterm>
<function>pg_get_indexdef</function> ( <parameter>index</parameter> <type>oid</type> <optional>, <parameter>column</parameter> <type>integer</type>, <parameter>pretty</parameter> <type>boolean</type> </optional> )
<returnvalue>text</returnvalue>
</para>
<para>
Reconstructs the creating command for an index.
(This is a decompiled reconstruction, not the original text
of the command.) If <parameter>column</parameter> is supplied and is
not zero, only the definition of that column is reconstructed.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_get_keywords</primary>
</indexterm>
<function>pg_get_keywords</function> ()
<returnvalue>setof record</returnvalue>
( <parameter>word</parameter> <type>text</type>,
<parameter>catcode</parameter> <type>"char"</type>,
<parameter>barelabel</parameter> <type>boolean</type>,
<parameter>catdesc</parameter> <type>text</type>,
<parameter>baredesc</parameter> <type>text</type> )
</para>
<para>
Returns a set of records describing the SQL keywords recognized by the
server. The <parameter>word</parameter> column contains the
keyword. The <parameter>catcode</parameter> column contains a
category code: <literal>U</literal> for an unreserved
keyword, <literal>C</literal> for a keyword that can be a column
name, <literal>T</literal> for a keyword that can be a type or
function name, or <literal>R</literal> for a fully reserved keyword.
The <parameter>barelabel</parameter> column
contains <literal>true</literal> if the keyword can be used as
a <quote>bare</quote> column label in <command>SELECT</command> lists,
or <literal>false</literal> if it can only be used
after <literal>AS</literal>.
The <parameter>catdesc</parameter> column contains a
possibly-localized string describing the keyword's category.
The <parameter>baredesc</parameter> column contains a
possibly-localized string describing the keyword's column label status.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_get_ruledef</primary>
</indexterm>
<function>pg_get_ruledef</function> ( <parameter>rule</parameter> <type>oid</type> <optional>, <parameter>pretty</parameter> <type>boolean</type> </optional> )
<returnvalue>text</returnvalue>
</para>
<para>
Reconstructs the creating command for a rule.
(This is a decompiled reconstruction, not the original text
of the command.)
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_get_serial_sequence</primary>
</indexterm>
<function>pg_get_serial_sequence</function> ( <parameter>table</parameter> <type>text</type>, <parameter>column</parameter> <type>text</type> )
<returnvalue>text</returnvalue>
</para>
<para>
Returns the name of the sequence associated with a column,
or NULL if no sequence is associated with the column.
If the column is an identity column, the associated sequence is the
sequence internally created for that column.
For columns created using one of the serial types
(<type>serial</type>, <type>smallserial</type>, <type>bigserial</type>),
it is the sequence created for that serial column definition.
In the latter case, the association can be modified or removed
with <command>ALTER SEQUENCE OWNED BY</command>.
(This function probably should have been
called <function>pg_get_owned_sequence</function>; its current name
reflects the fact that it has historically been used with serial-type
columns.) The first parameter is a table name with optional
schema, and the second parameter is a column name. Because the first
parameter potentially contains both schema and table names, it is
parsed per usual SQL rules, meaning it is lower-cased by default.
The second parameter, being just a column name, is treated literally
and so has its case preserved. The result is suitably formatted
for passing to the sequence functions (see
<xref linkend="functions-sequence"/>).
</para>
<para>
A typical use is in reading the current value of the sequence for an
identity or serial column, for example:
<programlisting>
SELECT currval(pg_get_serial_sequence('sometable', 'id'));
</programlisting>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_get_statisticsobjdef</primary>
</indexterm>
<function>pg_get_statisticsobjdef</function> ( <parameter>statobj</parameter> <type>oid</type> )
<returnvalue>text</returnvalue>
</para>
<para>
Reconstructs the creating command for an extended statistics object.
(This is a decompiled reconstruction, not the original text
of the command.)
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_get_triggerdef</primary>
</indexterm>
<function>pg_get_triggerdef</function> ( <parameter>trigger</parameter> <type>oid</type> <optional>, <parameter>pretty</parameter> <type>boolean</type> </optional> )
<returnvalue>text</returnvalue>
</para>
<para>
Reconstructs the creating command for a trigger.
(This is a decompiled reconstruction, not the original text
of the command.)
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_get_userbyid</primary>
</indexterm>
<function>pg_get_userbyid</function> ( <parameter>role</parameter> <type>oid</type> )
<returnvalue>name</returnvalue>
</para>
<para>
Returns a role's name given its OID.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_get_viewdef</primary>
</indexterm>
<function>pg_get_viewdef</function> ( <parameter>view</parameter> <type>oid</type> <optional>, <parameter>pretty</parameter> <type>boolean</type> </optional> )
<returnvalue>text</returnvalue>
</para>
<para>
Reconstructs the underlying <command>SELECT</command> command for a
view or materialized view. (This is a decompiled reconstruction, not
the original text of the command.)
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<function>pg_get_viewdef</function> ( <parameter>view</parameter> <type>oid</type>, <parameter>wrap_column</parameter> <type>integer</type> )
<returnvalue>text</returnvalue>
</para>
<para>
Reconstructs the underlying <command>SELECT</command> command for a
view or materialized view. (This is a decompiled reconstruction, not
the original text of the command.) In this form of the function,
pretty-printing is always enabled, and long lines are wrapped to try
to keep them shorter than the specified number of columns.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<function>pg_get_viewdef</function> ( <parameter>view</parameter> <type>text</type> <optional>, <parameter>pretty</parameter> <type>boolean</type> </optional> )
<returnvalue>text</returnvalue>
</para>
<para>
Reconstructs the underlying <command>SELECT</command> command for a
view or materialized view, working from a textual name for the view
rather than its OID. (This is deprecated; use the OID variant
instead.)
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_index_column_has_property</primary>
</indexterm>
<function>pg_index_column_has_property</function> ( <parameter>index</parameter> <type>regclass</type>, <parameter>column</parameter> <type>integer</type>, <parameter>property</parameter> <type>text</type> )
<returnvalue>boolean</returnvalue>
</para>
<para>
Tests whether an index column has the named property.
Common index column properties are listed in
<xref linkend="functions-info-index-column-props"/>.
(Note that extension access methods can define additional property
names for their indexes.)
<literal>NULL</literal> is returned if the property name is not known
or does not apply to the particular object, or if the OID or column
number does not identify a valid object.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_index_has_property</primary>
</indexterm>
<function>pg_index_has_property</function> ( <parameter>index</parameter> <type>regclass</type>, <parameter>property</parameter> <type>text</type> )
<returnvalue>boolean</returnvalue>
</para>
<para>
Tests whether an index has the named property.
Common index properties are listed in
<xref linkend="functions-info-index-props"/>.
(Note that extension access methods can define additional property
names for their indexes.)
<literal>NULL</literal> is returned if the property name is not known
or does not apply to the particular object, or if the OID does not
identify a valid object.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_indexam_has_property</primary>
</indexterm>
<function>pg_indexam_has_property</function> ( <parameter>am</parameter> <type>oid</type>, <parameter>property</parameter> <type>text</type> )
<returnvalue>boolean</returnvalue>
</para>
<para>
Tests whether an index access method has the named property.
Access method properties are listed in
<xref linkend="functions-info-indexam-props"/>.
<literal>NULL</literal> is returned if the property name is not known
or does not apply to the particular object, or if the OID does not
identify a valid object.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_options_to_table</primary>
</indexterm>
<function>pg_options_to_table</function> ( <parameter>options_array</parameter> <type>text[]</type> )
<returnvalue>setof record</returnvalue>
( <parameter>option_name</parameter> <type>text</type>,
<parameter>option_value</parameter> <type>text</type> )
</para>
<para>
Returns the set of storage options represented by a value from
<structname>pg_class</structname>.<structfield>reloptions</structfield> or
<structname>pg_attribute</structname>.<structfield>attoptions</structfield>.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_tablespace_databases</primary>
</indexterm>
<function>pg_tablespace_databases</function> ( <parameter>tablespace</parameter> <type>oid</type> )
<returnvalue>setof oid</returnvalue>
</para>
<para>
Returns the set of OIDs of databases that have objects stored in the
specified tablespace. If this function returns any rows, the
tablespace is not empty and cannot be dropped. To identify the specific
objects populating the tablespace, you will need to connect to the
database(s) identified by <function>pg_tablespace_databases</function>
and query their <structname>pg_class</structname> catalogs.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_tablespace_location</primary>
</indexterm>
<function>pg_tablespace_location</function> ( <parameter>tablespace</parameter> <type>oid</type> )
<returnvalue>text</returnvalue>
</para>
<para>
Returns the file system path that this tablespace is located in.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_typeof</primary>
</indexterm>
<function>pg_typeof</function> ( <type>"any"</type> )
<returnvalue>regtype</returnvalue>
</para>
<para>
Returns the OID of the data type of the value that is passed to it.
This can be helpful for troubleshooting or dynamically constructing
SQL queries. The function is declared as
returning <type>regtype</type>, which is an OID alias type (see
<xref linkend="datatype-oid"/>); this means that it is the same as an
OID for comparison purposes but displays as a type name.
</para>
<para>
For example:
<programlisting>
SELECT pg_typeof(33);
pg_typeof
-----------
integer
SELECT typlen FROM pg_type WHERE oid = pg_typeof(33);
typlen
--------
4
</programlisting>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>COLLATION FOR</primary>
</indexterm>
<function>COLLATION FOR</function> ( <type>"any"</type> )
<returnvalue>text</returnvalue>
</para>
<para>
Returns the name of the collation of the value that is passed to it.
The value is quoted and schema-qualified if necessary. If no
collation was derived for the argument expression,
then <literal>NULL</literal> is returned. If the argument is not of a
collatable data type, then an error is raised.
</para>
<para>
For example:
<programlisting>
SELECT collation for (description) FROM pg_description LIMIT 1;
pg_collation_for
------------------
"default"
SELECT collation for ('foo' COLLATE "de_DE");
pg_collation_for
------------------
"de_DE"
</programlisting>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>to_regclass</primary>
</indexterm>
<function>to_regclass</function> ( <type>text</type> )
<returnvalue>regclass</returnvalue>
</para>
<para>
Translates a textual relation name to its OID. A similar result is
obtained by casting the string to type <type>regclass</type> (see
<xref linkend="datatype-oid"/>); however, this function will return
<literal>NULL</literal> rather than throwing an error if the name is
not found. Also unlike the cast, this does not accept
a numeric OID as input.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>to_regcollation</primary>
</indexterm>
<function>to_regcollation</function> ( <type>text</type> )
<returnvalue>regcollation</returnvalue>
</para>
<para>
Translates a textual collation name to its OID. A similar result is
obtained by casting the string to type <type>regcollation</type> (see
<xref linkend="datatype-oid"/>); however, this function will return
<literal>NULL</literal> rather than throwing an error if the name is
not found. Also unlike the cast, this does not accept
a numeric OID as input.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>to_regnamespace</primary>
</indexterm>
<function>to_regnamespace</function> ( <type>text</type> )
<returnvalue>regnamespace</returnvalue>
</para>
<para>
Translates a textual schema name to its OID. A similar result is
obtained by casting the string to type <type>regnamespace</type> (see
<xref linkend="datatype-oid"/>); however, this function will return
<literal>NULL</literal> rather than throwing an error if the name is
not found. Also unlike the cast, this does not accept
a numeric OID as input.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>to_regoper</primary>
</indexterm>
<function>to_regoper</function> ( <type>text</type> )
<returnvalue>regoper</returnvalue>
</para>
<para>
Translates a textual operator name to its OID. A similar result is
obtained by casting the string to type <type>regoper</type> (see
<xref linkend="datatype-oid"/>); however, this function will return
<literal>NULL</literal> rather than throwing an error if the name is
not found or is ambiguous. Also unlike the cast, this does not accept
a numeric OID as input.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>to_regoperator</primary>
</indexterm>
<function>to_regoperator</function> ( <type>text</type> )
<returnvalue>regoperator</returnvalue>
</para>
<para>
Translates a textual operator name (with parameter types) to its OID. A similar result is
obtained by casting the string to type <type>regoperator</type> (see
<xref linkend="datatype-oid"/>); however, this function will return
<literal>NULL</literal> rather than throwing an error if the name is
not found. Also unlike the cast, this does not accept
a numeric OID as input.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>to_regproc</primary>
</indexterm>
<function>to_regproc</function> ( <type>text</type> )
<returnvalue>regproc</returnvalue>
</para>
<para>
Translates a textual function or procedure name to its OID. A similar result is
obtained by casting the string to type <type>regproc</type> (see
<xref linkend="datatype-oid"/>); however, this function will return
<literal>NULL</literal> rather than throwing an error if the name is
not found or is ambiguous. Also unlike the cast, this does not accept
a numeric OID as input.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>to_regprocedure</primary>
</indexterm>
<function>to_regprocedure</function> ( <type>text</type> )
<returnvalue>regprocedure</returnvalue>
</para>
<para>
Translates a textual function or procedure name (with argument types) to its OID. A similar result is
obtained by casting the string to type <type>regprocedure</type> (see
<xref linkend="datatype-oid"/>); however, this function will return
<literal>NULL</literal> rather than throwing an error if the name is
not found. Also unlike the cast, this does not accept
a numeric OID as input.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>to_regrole</primary>
</indexterm>
<function>to_regrole</function> ( <type>text</type> )
<returnvalue>regrole</returnvalue>
</para>
<para>
Translates a textual role name to its OID. A similar result is
obtained by casting the string to type <type>regrole</type> (see
<xref linkend="datatype-oid"/>); however, this function will return
<literal>NULL</literal> rather than throwing an error if the name is
not found. Also unlike the cast, this does not accept
a numeric OID as input.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>to_regtype</primary>
</indexterm>
<function>to_regtype</function> ( <type>text</type> )
<returnvalue>regtype</returnvalue>
</para>
<para>
Translates a textual type name to its OID. A similar result is
obtained by casting the string to type <type>regtype</type> (see
<xref linkend="datatype-oid"/>); however, this function will return
<literal>NULL</literal> rather than throwing an error if the name is
not found. Also unlike the cast, this does not accept
a numeric OID as input.
</para></entry>
</row>
</tbody>
</tgroup>
</table>
<para>
Most of the functions that reconstruct (decompile) database objects
have an optional <parameter>pretty</parameter> flag, which
if <literal>true</literal> causes the result to
be <quote>pretty-printed</quote>. Pretty-printing suppresses unnecessary
parentheses and adds whitespace for legibility.
The pretty-printed format is more readable, but the default format
is more likely to be interpreted the same way by future versions of
<productname>PostgreSQL</productname>; so avoid using pretty-printed output
for dump purposes. Passing <literal>false</literal> for
the <parameter>pretty</parameter> parameter yields the same result as
omitting the parameter.
</para>
<table id="functions-info-index-column-props">
<title>Index Column Properties</title>
<tgroup cols="2">
<thead>
<row><entry>Name</entry><entry>Description</entry></row>
</thead>
<tbody>
<row>
<entry><literal>asc</literal></entry>
<entry>Does the column sort in ascending order on a forward scan?
</entry>
</row>
<row>
<entry><literal>desc</literal></entry>
<entry>Does the column sort in descending order on a forward scan?
</entry>
</row>
<row>
<entry><literal>nulls_first</literal></entry>
<entry>Does the column sort with nulls first on a forward scan?
</entry>
</row>
<row>
<entry><literal>nulls_last</literal></entry>
<entry>Does the column sort with nulls last on a forward scan?
</entry>
</row>
<row>
<entry><literal>orderable</literal></entry>
<entry>Does the column possess any defined sort ordering?
</entry>
</row>
<row>
<entry><literal>distance_orderable</literal></entry>
<entry>Can the column be scanned in order by a <quote>distance</quote>
operator, for example <literal>ORDER BY col <-> constant</literal> ?
</entry>
</row>
<row>
<entry><literal>returnable</literal></entry>
<entry>Can the column value be returned by an index-only scan?
</entry>
</row>
<row>
<entry><literal>search_array</literal></entry>
<entry>Does the column natively support <literal>col = ANY(array)</literal>
searches?
</entry>
</row>
<row>
<entry><literal>search_nulls</literal></entry>
<entry>Does the column support <literal>IS NULL</literal> and
<literal>IS NOT NULL</literal> searches?
</entry>
</row>
</tbody>
</tgroup>
</table>
<table id="functions-info-index-props">
<title>Index Properties</title>
<tgroup cols="2">
<thead>
<row><entry>Name</entry><entry>Description</entry></row>
</thead>
<tbody>
<row>
<entry><literal>clusterable</literal></entry>
<entry>Can the index be used in a <literal>CLUSTER</literal> command?
</entry>
</row>
<row>
<entry><literal>index_scan</literal></entry>
<entry>Does the index support plain (non-bitmap) scans?
</entry>
</row>
<row>
<entry><literal>bitmap_scan</literal></entry>
<entry>Does the index support bitmap scans?
</entry>
</row>
<row>
<entry><literal>backward_scan</literal></entry>
<entry>Can the scan direction be changed in mid-scan (to
support <literal>FETCH BACKWARD</literal> on a cursor without
needing materialization)?
</entry>
</row>
</tbody>
</tgroup>
</table>
<table id="functions-info-indexam-props">
<title>Index Access Method Properties</title>
<tgroup cols="2">
<thead>
<row><entry>Name</entry><entry>Description</entry></row>
</thead>
<tbody>
<row>
<entry><literal>can_order</literal></entry>
<entry>Does the access method support <literal>ASC</literal>,
<literal>DESC</literal> and related keywords in
<literal>CREATE INDEX</literal>?
</entry>
</row>
<row>
<entry><literal>can_unique</literal></entry>
<entry>Does the access method support unique indexes?
</entry>
</row>
<row>
<entry><literal>can_multi_col</literal></entry>
<entry>Does the access method support indexes with multiple columns?
</entry>
</row>
<row>
<entry><literal>can_exclude</literal></entry>
<entry>Does the access method support exclusion constraints?
</entry>
</row>
<row>
<entry><literal>can_include</literal></entry>
<entry>Does the access method support the <literal>INCLUDE</literal>
clause of <literal>CREATE INDEX</literal>?
</entry>
</row>
</tbody>
</tgroup>
</table>
<para>
<xref linkend="functions-info-object-table"/> lists functions related to
database object identification and addressing.
</para>
<table id="functions-info-object-table">
<title>Object Information and Addressing Functions</title>
<tgroup cols="1">
<thead>
<row>
<entry role="func_table_entry"><para role="func_signature">
Function
</para>
<para>
Description
</para></entry>
</row>
</thead>
<tbody>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_describe_object</primary>
</indexterm>
<function>pg_describe_object</function> ( <parameter>classid</parameter> <type>oid</type>, <parameter>objid</parameter> <type>oid</type>, <parameter>objsubid</parameter> <type>integer</type> )
<returnvalue>text</returnvalue>
</para>
<para>
Returns a textual description of a database object identified by
catalog OID, object OID, and sub-object ID (such as a column number
within a table; the sub-object ID is zero when referring to a whole
object). This description is intended to be human-readable, and might
be translated, depending on server configuration. This is especially
useful to determine the identity of an object referenced in the
<structname>pg_depend</structname> catalog. This function returns
<literal>NULL</literal> values for undefined objects.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_identify_object</primary>
</indexterm>
<function>pg_identify_object</function> ( <parameter>classid</parameter> <type>oid</type>, <parameter>objid</parameter> <type>oid</type>, <parameter>objsubid</parameter> <type>integer</type> )
<returnvalue>record</returnvalue>
( <parameter>type</parameter> <type>text</type>,
<parameter>schema</parameter> <type>text</type>,
<parameter>name</parameter> <type>text</type>,
<parameter>identity</parameter> <type>text</type> )
</para>
<para>
Returns a row containing enough information to uniquely identify the
database object specified by catalog OID, object OID and sub-object
ID.
This information is intended to be machine-readable, and is never
translated.
<parameter>type</parameter> identifies the type of database object;
<parameter>schema</parameter> is the schema name that the object
belongs in, or <literal>NULL</literal> for object types that do not
belong to schemas;
<parameter>name</parameter> is the name of the object, quoted if
necessary, if the name (along with schema name, if pertinent) is
sufficient to uniquely identify the object,
otherwise <literal>NULL</literal>;
<parameter>identity</parameter> is the complete object identity, with
the precise format depending on object type, and each name within the
format being schema-qualified and quoted as necessary. Undefined
objects are identified with <literal>NULL</literal> values.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_identify_object_as_address</primary>
</indexterm>
<function>pg_identify_object_as_address</function> ( <parameter>classid</parameter> <type>oid</type>, <parameter>objid</parameter> <type>oid</type>, <parameter>objsubid</parameter> <type>integer</type> )
<returnvalue>record</returnvalue>
( <parameter>type</parameter> <type>text</type>,
<parameter>object_names</parameter> <type>text[]</type>,
<parameter>object_args</parameter> <type>text[]</type> )
</para>
<para>
Returns a row containing enough information to uniquely identify the
database object specified by catalog OID, object OID and sub-object
ID.
The returned information is independent of the current server, that
is, it could be used to identify an identically named object in
another server.
<parameter>type</parameter> identifies the type of database object;
<parameter>object_names</parameter> and
<parameter>object_args</parameter>
are text arrays that together form a reference to the object.
These three values can be passed
to <function>pg_get_object_address</function> to obtain the internal
address of the object.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_get_object_address</primary>
</indexterm>
<function>pg_get_object_address</function> ( <parameter>type</parameter> <type>text</type>, <parameter>object_names</parameter> <type>text[]</type>, <parameter>object_args</parameter> <type>text[]</type> )
<returnvalue>record</returnvalue>
( <parameter>classid</parameter> <type>oid</type>,
<parameter>objid</parameter> <type>oid</type>,
<parameter>objsubid</parameter> <type>integer</type> )
</para>
<para>
Returns a row containing enough information to uniquely identify the
database object specified by a type code and object name and argument
arrays.
The returned values are the ones that would be used in system catalogs
such as <structname>pg_depend</structname>; they can be passed to
other system functions such as <function>pg_describe_object</function>
or <function>pg_identify_object</function>.
<parameter>classid</parameter> is the OID of the system catalog
containing the object;
<parameter>objid</parameter> is the OID of the object itself, and
<parameter>objsubid</parameter> is the sub-object ID, or zero if none.
This function is the inverse
of <function>pg_identify_object_as_address</function>.
Undefined objects are identified with <literal>NULL</literal> values.
</para></entry>
</row>
</tbody>
</tgroup>
</table>
<indexterm>
<primary>comment</primary>
<secondary sortas="database objects">about database objects</secondary>
</indexterm>
<para>
The functions shown in <xref linkend="functions-info-comment-table"/>
extract comments previously stored with the <xref linkend="sql-comment"/>
command. A null value is returned if no
comment could be found for the specified parameters.
</para>
<table id="functions-info-comment-table">
<title>Comment Information Functions</title>
<tgroup cols="1">
<thead>
<row>
<entry role="func_table_entry"><para role="func_signature">
Function
</para>
<para>
Description
</para></entry>
</row>
</thead>
<tbody>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>col_description</primary>
</indexterm>
<function>col_description</function> ( <parameter>table</parameter> <type>oid</type>, <parameter>column</parameter> <type>integer</type> )
<returnvalue>text</returnvalue>
</para>
<para>
Returns the comment for a table column, which is specified by the OID
of its table and its column number.
(<function>obj_description</function> cannot be used for table
columns, since columns do not have OIDs of their own.)
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>obj_description</primary>
</indexterm>
<function>obj_description</function> ( <parameter>object</parameter> <type>oid</type>, <parameter>catalog</parameter> <type>name</type> )
<returnvalue>text</returnvalue>
</para>
<para>
Returns the comment for a database object specified by its OID and the
name of the containing system catalog. For
example, <literal>obj_description(123456, 'pg_class')</literal> would
retrieve the comment for the table with OID 123456.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<function>obj_description</function> ( <parameter>object</parameter> <type>oid</type> )
<returnvalue>text</returnvalue>
</para>
<para>
Returns the comment for a database object specified by its OID alone.
This is <emphasis>deprecated</emphasis> since there is no guarantee
that OIDs are unique across different system catalogs; therefore, the
wrong comment might be returned.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>shobj_description</primary>
</indexterm>
<function>shobj_description</function> ( <parameter>object</parameter> <type>oid</type>, <parameter>catalog</parameter> <type>name</type> )
<returnvalue>text</returnvalue>
</para>
<para>
Returns the comment for a shared database object specified by its OID
and the name of the containing system catalog. This is just
like <function>obj_description</function> except that it is used for
retrieving comments on shared objects (that is, databases, roles, and
tablespaces). Some system catalogs are global to all databases within
each cluster, and the descriptions for objects in them are stored
globally as well.
</para></entry>
</row>
</tbody>
</tgroup>
</table>
<para>
The functions shown in <xref linkend="functions-pg-snapshot"/>
provide server transaction information in an exportable form. The main
use of these functions is to determine which transactions were committed
between two snapshots.
</para>
<table id="functions-pg-snapshot">
<title>Transaction ID and Snapshot Information Functions</title>
<tgroup cols="1">
<thead>
<row>
<entry role="func_table_entry"><para role="func_signature">
Function
</para>
<para>
Description
</para></entry>
</row>
</thead>
<tbody>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_current_xact_id</primary>
</indexterm>
<function>pg_current_xact_id</function> ()
<returnvalue>xid8</returnvalue>
</para>
<para>
Returns the current transaction's ID. It will assign a new one if the
current transaction does not have one already (because it has not
performed any database updates).
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_current_xact_id_if_assigned</primary>
</indexterm>
<function>pg_current_xact_id_if_assigned</function> ()
<returnvalue>xid8</returnvalue>
</para>
<para>
Returns the current transaction's ID, or <literal>NULL</literal> if no
ID is assigned yet. (It's best to use this variant if the transaction
might otherwise be read-only, to avoid unnecessary consumption of an
XID.)
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_xact_status</primary>
</indexterm>
<function>pg_xact_status</function> ( <type>xid8</type> )
<returnvalue>text</returnvalue>
</para>
<para>
Reports the commit status of a recent transaction.
The result is one of <literal>in progress</literal>,
<literal>committed</literal>, or <literal>aborted</literal>,
provided that the transaction is recent enough that the system retains
the commit status of that transaction.
If it is old enough that no references to the transaction survive in
the system and the commit status information has been discarded, the
result is <literal>NULL</literal>.
Applications might use this function, for example, to determine
whether their transaction committed or aborted after the application
and database server become disconnected while
a <literal>COMMIT</literal> is in progress.
Note that prepared transactions are reported as <literal>in
progress</literal>; applications must check <link
linkend="view-pg-prepared-xacts"><structname>pg_prepared_xacts</structname></link>
if they need to determine whether a transaction ID belongs to a
prepared transaction.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_current_snapshot</primary>
</indexterm>
<function>pg_current_snapshot</function> ()
<returnvalue>pg_snapshot</returnvalue>
</para>
<para>
Returns a current <firstterm>snapshot</firstterm>, a data structure
showing which transaction IDs are now in-progress.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_snapshot_xip</primary>
</indexterm>
<function>pg_snapshot_xip</function> ( <type>pg_snapshot</type> )
<returnvalue>setof xid8</returnvalue>
</para>
<para>
Returns the set of in-progress transaction IDs contained in a snapshot.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_snapshot_xmax</primary>
</indexterm>
<function>pg_snapshot_xmax</function> ( <type>pg_snapshot</type> )
<returnvalue>xid8</returnvalue>
</para>
<para>
Returns the <structfield>xmax</structfield> of a snapshot.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_snapshot_xmin</primary>
</indexterm>
<function>pg_snapshot_xmin</function> ( <type>pg_snapshot</type> )
<returnvalue>xid8</returnvalue>
</para>
<para>
Returns the <structfield>xmin</structfield> of a snapshot.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_visible_in_snapshot</primary>
</indexterm>
<function>pg_visible_in_snapshot</function> ( <type>xid8</type>, <type>pg_snapshot</type> )
<returnvalue>boolean</returnvalue>
</para>
<para>
Is the given transaction ID <firstterm>visible</firstterm> according
to this snapshot (that is, was it completed before the snapshot was
taken)? Note that this function will not give the correct answer for
a subtransaction ID.
</para></entry>
</row>
</tbody>
</tgroup>
</table>
<para>
The internal transaction ID type <type>xid</type> is 32 bits wide and
wraps around every 4 billion transactions. However,
the functions shown in <xref linkend="functions-pg-snapshot"/> use a
64-bit type <type>xid8</type> that does not wrap around during the life
of an installation, and can be converted to <type>xid</type> by casting if
required. The data type <type>pg_snapshot</type> stores information about
transaction ID visibility at a particular moment in time. Its components
are described in <xref linkend="functions-pg-snapshot-parts"/>.
<type>pg_snapshot</type>'s textual representation is
<literal><replaceable>xmin</replaceable>:<replaceable>xmax</replaceable>:<replaceable>xip_list</replaceable></literal>.
For example <literal>10:20:10,14,15</literal> means
<literal>xmin=10, xmax=20, xip_list=10, 14, 15</literal>.
</para>
<table id="functions-pg-snapshot-parts">
<title>Snapshot Components</title>
<tgroup cols="2">
<thead>
<row>
<entry>Name</entry>
<entry>Description</entry>
</row>
</thead>
<tbody>
<row>
<entry><structfield>xmin</structfield></entry>
<entry>
Lowest transaction ID that was still active. All transaction IDs
less than <structfield>xmin</structfield> are either committed and visible,
or rolled back and dead.
</entry>
</row>
<row>
<entry><structfield>xmax</structfield></entry>
<entry>
One past the highest completed transaction ID. All transaction IDs
greater than or equal to <structfield>xmax</structfield> had not yet
completed as of the time of the snapshot, and thus are invisible.
</entry>
</row>
<row>
<entry><structfield>xip_list</structfield></entry>
<entry>
Transactions in progress at the time of the snapshot. A transaction
ID that is <literal>xmin <= <replaceable>X</replaceable> <
xmax</literal> and not in this list was already completed at the time
of the snapshot, and thus is either visible or dead according to its
commit status. This list does not include the transaction IDs of
subtransactions.
</entry>
</row>
</tbody>
</tgroup>
</table>
<para>
In releases of <productname>PostgreSQL</productname> before 13 there was
no <type>xid8</type> type, so variants of these functions were provided
that used <type>bigint</type> to represent a 64-bit XID, with a
correspondingly distinct snapshot data type <type>txid_snapshot</type>.
These older functions have <literal>txid</literal> in their names. They
are still supported for backward compatibility, but may be removed from a
future release. See <xref linkend="functions-txid-snapshot"/>.
</para>
<table id="functions-txid-snapshot">
<title>Deprecated Transaction ID and Snapshot Information Functions</title>
<tgroup cols="1">
<thead>
<row>
<entry role="func_table_entry"><para role="func_signature">
Function
</para>
<para>
Description
</para></entry>
</row>
</thead>
<tbody>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>txid_current</primary>
</indexterm>
<function>txid_current</function> ()
<returnvalue>bigint</returnvalue>
</para>
<para>
See <function>pg_current_xact_id()</function>.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>txid_current_if_assigned</primary>
</indexterm>
<function>txid_current_if_assigned</function> ()
<returnvalue>bigint</returnvalue>
</para>
<para>
See <function>pg_current_xact_id_if_assigned()</function>.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>txid_current_snapshot</primary>
</indexterm>
<function>txid_current_snapshot</function> ()
<returnvalue>txid_snapshot</returnvalue>
</para>
<para>
See <function>pg_current_snapshot()</function>.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>txid_snapshot_xip</primary>
</indexterm>
<function>txid_snapshot_xip</function> ( <type>txid_snapshot</type> )
<returnvalue>setof bigint</returnvalue>
</para>
<para>
See <function>pg_snapshot_xip()</function>.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>txid_snapshot_xmax</primary>
</indexterm>
<function>txid_snapshot_xmax</function> ( <type>txid_snapshot</type> )
<returnvalue>bigint</returnvalue>
</para>
<para>
See <function>pg_snapshot_xmax()</function>.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>txid_snapshot_xmin</primary>
</indexterm>
<function>txid_snapshot_xmin</function> ( <type>txid_snapshot</type> )
<returnvalue>bigint</returnvalue>
</para>
<para>
See <function>pg_snapshot_xmin()</function>.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>txid_visible_in_snapshot</primary>
</indexterm>
<function>txid_visible_in_snapshot</function> ( <type>bigint</type>, <type>txid_snapshot</type> )
<returnvalue>boolean</returnvalue>
</para>
<para>
See <function>pg_visible_in_snapshot()</function>.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>txid_status</primary>
</indexterm>
<function>txid_status</function> ( <type>bigint</type> )
<returnvalue>text</returnvalue>
</para>
<para>
See <function>pg_xact_status()</function>.
</para></entry>
</row>
</tbody>
</tgroup>
</table>
<para>
The functions shown in <xref linkend="functions-commit-timestamp"/>
provide information about when past transactions were committed.
They only provide useful data when the
<xref linkend="guc-track-commit-timestamp"/> configuration option is
enabled, and only for transactions that were committed after it was
enabled.
</para>
<table id="functions-commit-timestamp">
<title>Committed Transaction Information Functions</title>
<tgroup cols="1">
<thead>
<row>
<entry role="func_table_entry"><para role="func_signature">
Function
</para>
<para>
Description
</para></entry>
</row>
</thead>
<tbody>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_xact_commit_timestamp</primary>
</indexterm>
<function>pg_xact_commit_timestamp</function> ( <type>xid</type> )
<returnvalue>timestamp with time zone</returnvalue>
</para>
<para>
Returns the commit timestamp of a transaction.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_xact_commit_timestamp_origin</primary>
</indexterm>
<function>pg_xact_commit_timestamp_origin</function> ( <type>xid</type> )
<returnvalue>record</returnvalue>
( <parameter>timestamp</parameter> <type>timestamp with time zone</type>,
<parameter>roident</parameter> <type>oid</type>)
</para>
<para>
Returns the commit timestamp and replication origin of a transaction.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_last_committed_xact</primary>
</indexterm>
<function>pg_last_committed_xact</function> ()
<returnvalue>record</returnvalue>
( <parameter>xid</parameter> <type>xid</type>,
<parameter>timestamp</parameter> <type>timestamp with time zone</type>,
<parameter>roident</parameter> <type>oid</type> )
</para>
<para>
Returns the transaction ID, commit timestamp and replication origin
of the latest committed transaction.
</para></entry>
</row>
</tbody>
</tgroup>
</table>
<para>
The functions shown in <xref linkend="functions-controldata"/>
print information initialized during <command>initdb</command>, such
as the catalog version. They also show information about write-ahead
logging and checkpoint processing. This information is cluster-wide,
not specific to any one database. These functions provide most of the same
information, from the same source, as the
<xref linkend="app-pgcontroldata"/> application.
</para>
<table id="functions-controldata">
<title>Control Data Functions</title>
<tgroup cols="1">
<thead>
<row>
<entry role="func_table_entry"><para role="func_signature">
Function
</para>
<para>
Description
</para></entry>
</row>
</thead>
<tbody>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_control_checkpoint</primary>
</indexterm>
<function>pg_control_checkpoint</function> ()
<returnvalue>record</returnvalue>
</para>
<para>
Returns information about current checkpoint state, as shown in
<xref linkend="functions-pg-control-checkpoint"/>.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_control_system</primary>
</indexterm>
<function>pg_control_system</function> ()
<returnvalue>record</returnvalue>
</para>
<para>
Returns information about current control file state, as shown in
<xref linkend="functions-pg-control-system"/>.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_control_init</primary>
</indexterm>
<function>pg_control_init</function> ()
<returnvalue>record</returnvalue>
</para>
<para>
Returns information about cluster initialization state, as shown in
<xref linkend="functions-pg-control-init"/>.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_control_recovery</primary>
</indexterm>
<function>pg_control_recovery</function> ()
<returnvalue>record</returnvalue>
</para>
<para>
Returns information about recovery state, as shown in
<xref linkend="functions-pg-control-recovery"/>.
</para></entry>
</row>
</tbody>
</tgroup>
</table>
<table id="functions-pg-control-checkpoint">
<title><function>pg_control_checkpoint</function> Output Columns</title>
<tgroup cols="2">
<thead>
<row>
<entry>Column Name</entry>
<entry>Data Type</entry>
</row>
</thead>
<tbody>
<row>
<entry><structfield>checkpoint_lsn</structfield></entry>
<entry><type>pg_lsn</type></entry>
</row>
<row>
<entry><structfield>redo_lsn</structfield></entry>
<entry><type>pg_lsn</type></entry>
</row>
<row>
<entry><structfield>redo_wal_file</structfield></entry>
<entry><type>text</type></entry>
</row>
<row>
<entry><structfield>timeline_id</structfield></entry>
<entry><type>integer</type></entry>
</row>
<row>
<entry><structfield>prev_timeline_id</structfield></entry>
<entry><type>integer</type></entry>
</row>
<row>
<entry><structfield>full_page_writes</structfield></entry>
<entry><type>boolean</type></entry>
</row>
<row>
<entry><structfield>next_xid</structfield></entry>
<entry><type>text</type></entry>
</row>
<row>
<entry><structfield>next_oid</structfield></entry>
<entry><type>oid</type></entry>
</row>
<row>
<entry><structfield>next_multixact_id</structfield></entry>
<entry><type>xid</type></entry>
</row>
<row>
<entry><structfield>next_multi_offset</structfield></entry>
<entry><type>xid</type></entry>
</row>
<row>
<entry><structfield>oldest_xid</structfield></entry>
<entry><type>xid</type></entry>
</row>
<row>
<entry><structfield>oldest_xid_dbid</structfield></entry>
<entry><type>oid</type></entry>
</row>
<row>
<entry><structfield>oldest_active_xid</structfield></entry>
<entry><type>xid</type></entry>
</row>
<row>
<entry><structfield>oldest_multi_xid</structfield></entry>
<entry><type>xid</type></entry>
</row>
<row>
<entry><structfield>oldest_multi_dbid</structfield></entry>
<entry><type>oid</type></entry>
</row>
<row>
<entry><structfield>oldest_commit_ts_xid</structfield></entry>
<entry><type>xid</type></entry>
</row>
<row>
<entry><structfield>newest_commit_ts_xid</structfield></entry>
<entry><type>xid</type></entry>
</row>
<row>
<entry><structfield>checkpoint_time</structfield></entry>
<entry><type>timestamp with time zone</type></entry>
</row>
</tbody>
</tgroup>
</table>
<table id="functions-pg-control-system">
<title><function>pg_control_system</function> Output Columns</title>
<tgroup cols="2">
<thead>
<row>
<entry>Column Name</entry>
<entry>Data Type</entry>
</row>
</thead>
<tbody>
<row>
<entry><structfield>pg_control_version</structfield></entry>
<entry><type>integer</type></entry>
</row>
<row>
<entry><structfield>catalog_version_no</structfield></entry>
<entry><type>integer</type></entry>
</row>
<row>
<entry><structfield>system_identifier</structfield></entry>
<entry><type>bigint</type></entry>
</row>
<row>
<entry><structfield>pg_control_last_modified</structfield></entry>
<entry><type>timestamp with time zone</type></entry>
</row>
</tbody>
</tgroup>
</table>
<table id="functions-pg-control-init">
<title><function>pg_control_init</function> Output Columns</title>
<tgroup cols="2">
<thead>
<row>
<entry>Column Name</entry>
<entry>Data Type</entry>
</row>
</thead>
<tbody>
<row>
<entry><structfield>max_data_alignment</structfield></entry>
<entry><type>integer</type></entry>
</row>
<row>
<entry><structfield>database_block_size</structfield></entry>
<entry><type>integer</type></entry>
</row>
<row>
<entry><structfield>blocks_per_segment</structfield></entry>
<entry><type>integer</type></entry>
</row>
<row>
<entry><structfield>wal_block_size</structfield></entry>
<entry><type>integer</type></entry>
</row>
<row>
<entry><structfield>bytes_per_wal_segment</structfield></entry>
<entry><type>integer</type></entry>
</row>
<row>
<entry><structfield>max_identifier_length</structfield></entry>
<entry><type>integer</type></entry>
</row>
<row>
<entry><structfield>max_index_columns</structfield></entry>
<entry><type>integer</type></entry>
</row>
<row>
<entry><structfield>max_toast_chunk_size</structfield></entry>
<entry><type>integer</type></entry>
</row>
<row>
<entry><structfield>large_object_chunk_size</structfield></entry>
<entry><type>integer</type></entry>
</row>
<row>
<entry><structfield>float8_pass_by_value</structfield></entry>
<entry><type>boolean</type></entry>
</row>
<row>
<entry><structfield>data_page_checksum_version</structfield></entry>
<entry><type>integer</type></entry>
</row>
</tbody>
</tgroup>
</table>
<table id="functions-pg-control-recovery">
<title><function>pg_control_recovery</function> Output Columns</title>
<tgroup cols="2">
<thead>
<row>
<entry>Column Name</entry>
<entry>Data Type</entry>
</row>
</thead>
<tbody>
<row>
<entry><structfield>min_recovery_end_lsn</structfield></entry>
<entry><type>pg_lsn</type></entry>
</row>
<row>
<entry><structfield>min_recovery_end_timeline</structfield></entry>
<entry><type>integer</type></entry>
</row>
<row>
<entry><structfield>backup_start_lsn</structfield></entry>
<entry><type>pg_lsn</type></entry>
</row>
<row>
<entry><structfield>backup_end_lsn</structfield></entry>
<entry><type>pg_lsn</type></entry>
</row>
<row>
<entry><structfield>end_of_backup_record_required</structfield></entry>
<entry><type>boolean</type></entry>
</row>
</tbody>
</tgroup>
</table>
</sect1>
<sect1 id="functions-admin">
<title>System Administration Functions</title>
<para>
The functions described in this section are used to control and
monitor a <productname>PostgreSQL</productname> installation.
</para>
<sect2 id="functions-admin-set">
<title>Configuration Settings Functions</title>
<indexterm>
<primary>SET</primary>
</indexterm>
<indexterm>
<primary>SHOW</primary>
</indexterm>
<indexterm>
<primary>configuration</primary>
<secondary sortas="server">of the server</secondary>
<tertiary>functions</tertiary>
</indexterm>
<para>
<xref linkend="functions-admin-set-table"/> shows the functions
available to query and alter run-time configuration parameters.
</para>
<table id="functions-admin-set-table">
<title>Configuration Settings Functions</title>
<tgroup cols="1">
<thead>
<row>
<entry role="func_table_entry"><para role="func_signature">
Function
</para>
<para>
Description
</para>
<para>
Example(s)
</para></entry>
</row>
</thead>
<tbody>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>current_setting</primary>
</indexterm>
<function>current_setting</function> ( <parameter>setting_name</parameter> <type>text</type> <optional>, <parameter>missing_ok</parameter> <type>boolean</type> </optional> )
<returnvalue>text</returnvalue>
</para>
<para>
Returns the current value of the
setting <parameter>setting_name</parameter>. If there is no such
setting, <function>current_setting</function> throws an error
unless <parameter>missing_ok</parameter> is supplied and
is <literal>true</literal> (in which case NULL is returned).
This function corresponds to
the <acronym>SQL</acronym> command <xref linkend="sql-show"/>.
</para>
<para>
<literal>current_setting('datestyle')</literal>
<returnvalue>ISO, MDY</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>set_config</primary>
</indexterm>
<function>set_config</function> (
<parameter>setting_name</parameter> <type>text</type>,
<parameter>new_value</parameter> <type>text</type>,
<parameter>is_local</parameter> <type>boolean</type> )
<returnvalue>text</returnvalue>
</para>
<para>
Sets the parameter <parameter>setting_name</parameter>
to <parameter>new_value</parameter>, and returns that value.
If <parameter>is_local</parameter> is <literal>true</literal>, the new
value will only apply during the current transaction. If you want the
new value to apply for the rest of the current session,
use <literal>false</literal> instead. This function corresponds to
the SQL command <xref linkend="sql-set"/>.
</para>
<para>
<literal>set_config('log_statement_stats', 'off', false)</literal>
<returnvalue>off</returnvalue>
</para></entry>
</row>
</tbody>
</tgroup>
</table>
</sect2>
<sect2 id="functions-admin-signal">
<title>Server Signaling Functions</title>
<indexterm>
<primary>signal</primary>
<secondary sortas="backend">backend processes</secondary>
</indexterm>
<para>
The functions shown in <xref
linkend="functions-admin-signal-table"/> send control signals to
other server processes. Use of these functions is restricted to
superusers by default but access may be granted to others using
<command>GRANT</command>, with noted exceptions.
</para>
<para>
Each of these functions returns <literal>true</literal> if
the signal was successfully sent and <literal>false</literal>
if sending the signal failed.
</para>
<table id="functions-admin-signal-table">
<title>Server Signaling Functions</title>
<tgroup cols="1">
<thead>
<row>
<entry role="func_table_entry"><para role="func_signature">
Function
</para>
<para>
Description
</para></entry>
</row>
</thead>
<tbody>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_cancel_backend</primary>
</indexterm>
<function>pg_cancel_backend</function> ( <parameter>pid</parameter> <type>integer</type> )
<returnvalue>boolean</returnvalue>
</para>
<para>
Cancels the current query of the session whose backend process has the
specified process ID. This is also allowed if the
calling role is a member of the role whose backend is being canceled or
the calling role has been granted <literal>pg_signal_backend</literal>,
however only superusers can cancel superuser backends.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_log_backend_memory_contexts</primary>
</indexterm>
<function>pg_log_backend_memory_contexts</function> ( <parameter>pid</parameter> <type>integer</type> )
<returnvalue>boolean</returnvalue>
</para>
<para>
Requests to log the memory contexts of the backend with the
specified process ID. These memory contexts will be logged at
<literal>LOG</literal> message level. They will appear in
the server log based on the log configuration set
(See <xref linkend="runtime-config-logging"/> for more information),
but will not be sent to the client regardless of
<xref linkend="guc-client-min-messages"/>.
Only superusers can request to log the memory contexts.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_reload_conf</primary>
</indexterm>
<function>pg_reload_conf</function> ()
<returnvalue>boolean</returnvalue>
</para>
<para>
Causes all processes of the <productname>PostgreSQL</productname>
server to reload their configuration files. (This is initiated by
sending a <systemitem>SIGHUP</systemitem> signal to the postmaster
process, which in turn sends <systemitem>SIGHUP</systemitem> to each
of its children.) You can use the
<link linkend="view-pg-file-settings"><structname>pg_file_settings</structname></link> and
<link linkend="view-pg-hba-file-rules"><structname>pg_hba_file_rules</structname></link> views
to check the configuration files for possible errors, before reloading.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_rotate_logfile</primary>
</indexterm>
<function>pg_rotate_logfile</function> ()
<returnvalue>boolean</returnvalue>
</para>
<para>
Signals the log-file manager to switch to a new output file
immediately. This works only when the built-in log collector is
running, since otherwise there is no log-file manager subprocess.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_terminate_backend</primary>
</indexterm>
<function>pg_terminate_backend</function> ( <parameter>pid</parameter> <type>integer</type>, <parameter>timeout</parameter> <type>bigint</type> <literal>DEFAULT</literal> <literal>0</literal> )
<returnvalue>boolean</returnvalue>
</para>
<para>
Terminates the session whose backend process has the
specified process ID. This is also allowed if the calling role
is a member of the role whose backend is being terminated or the
calling role has been granted <literal>pg_signal_backend</literal>,
however only superusers can terminate superuser backends.
</para>
<para>
If <parameter>timeout</parameter> is not specified or zero, this
function returns <literal>true</literal> whether the process actually
terminates or not, indicating only that the sending of the signal was
successful. If the <parameter>timeout</parameter> is specified (in
milliseconds) and greater than zero, the function waits until the
process is actually terminated or until the given time has passed. If
the process is terminated, the function
returns <literal>true</literal>. On timeout, a warning is emitted and
<literal>false</literal> is returned.
</para></entry>
</row>
</tbody>
</tgroup>
</table>
<para>
<function>pg_cancel_backend</function> and <function>pg_terminate_backend</function>
send signals (<systemitem>SIGINT</systemitem> or <systemitem>SIGTERM</systemitem>
respectively) to backend processes identified by process ID.
The process ID of an active backend can be found from
the <structfield>pid</structfield> column of the
<structname>pg_stat_activity</structname> view, or by listing the
<command>postgres</command> processes on the server (using
<application>ps</application> on Unix or the <application>Task
Manager</application> on <productname>Windows</productname>).
The role of an active backend can be found from the
<structfield>usename</structfield> column of the
<structname>pg_stat_activity</structname> view.
</para>
<para>
<function>pg_log_backend_memory_contexts</function> can be used
to log the memory contexts of a backend process. For example:
<programlisting>
postgres=# SELECT pg_log_backend_memory_contexts(pg_backend_pid());
pg_log_backend_memory_contexts
--------------------------------
t
(1 row)
</programlisting>
One message for each memory context will be logged. For example:
<screen>
LOG: logging memory contexts of PID 10377
STATEMENT: SELECT pg_log_backend_memory_contexts(pg_backend_pid());
LOG: level: 0; TopMemoryContext: 80800 total in 6 blocks; 14432 free (5 chunks); 66368 used
LOG: level: 1; pgstat TabStatusArray lookup hash table: 8192 total in 1 blocks; 1408 free (0 chunks); 6784 used
LOG: level: 1; TopTransactionContext: 8192 total in 1 blocks; 7720 free (1 chunks); 472 used
LOG: level: 1; RowDescriptionContext: 8192 total in 1 blocks; 6880 free (0 chunks); 1312 used
LOG: level: 1; MessageContext: 16384 total in 2 blocks; 5152 free (0 chunks); 11232 used
LOG: level: 1; Operator class cache: 8192 total in 1 blocks; 512 free (0 chunks); 7680 used
LOG: level: 1; smgr relation table: 16384 total in 2 blocks; 4544 free (3 chunks); 11840 used
LOG: level: 1; TransactionAbortContext: 32768 total in 1 blocks; 32504 free (0 chunks); 264 used
...
LOG: level: 1; ErrorContext: 8192 total in 1 blocks; 7928 free (3 chunks); 264 used
LOG: Grand total: 1651920 bytes in 201 blocks; 622360 free (88 chunks); 1029560 used
</screen>
If there are more than 100 child contexts under the same parent, the first
100 child contexts are logged, along with a summary of the remaining contexts.
Note that frequent calls to this function could incur significant overhead,
because it may generate a large number of log messages.
</para>
</sect2>
<sect2 id="functions-admin-backup">
<title>Backup Control Functions</title>
<indexterm>
<primary>backup</primary>
</indexterm>
<para>
The functions shown in <xref
linkend="functions-admin-backup-table"/> assist in making on-line backups.
These functions cannot be executed during recovery (except
non-exclusive <function>pg_start_backup</function>,
non-exclusive <function>pg_stop_backup</function>,
<function>pg_is_in_backup</function>, <function>pg_backup_start_time</function>
and <function>pg_wal_lsn_diff</function>).
</para>
<para>
For details about proper usage of these functions, see
<xref linkend="continuous-archiving"/>.
</para>
<table id="functions-admin-backup-table">
<title>Backup Control Functions</title>
<tgroup cols="1">
<thead>
<row>
<entry role="func_table_entry"><para role="func_signature">
Function
</para>
<para>
Description
</para></entry>
</row>
</thead>
<tbody>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_create_restore_point</primary>
</indexterm>
<function>pg_create_restore_point</function> ( <parameter>name</parameter> <type>text</type> )
<returnvalue>pg_lsn</returnvalue>
</para>
<para>
Creates a named marker record in the write-ahead log that can later be
used as a recovery target, and returns the corresponding write-ahead
log location. The given name can then be used with
<xref linkend="guc-recovery-target-name"/> to specify the point up to
which recovery will proceed. Avoid creating multiple restore points
with the same name, since recovery will stop at the first one whose
name matches the recovery target.
</para>
<para>
This function is restricted to superusers by default, but other users
can be granted EXECUTE to run the function.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_current_wal_flush_lsn</primary>
</indexterm>
<function>pg_current_wal_flush_lsn</function> ()
<returnvalue>pg_lsn</returnvalue>
</para>
<para>
Returns the current write-ahead log flush location (see notes below).
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_current_wal_insert_lsn</primary>
</indexterm>
<function>pg_current_wal_insert_lsn</function> ()
<returnvalue>pg_lsn</returnvalue>
</para>
<para>
Returns the current write-ahead log insert location (see notes below).
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_current_wal_lsn</primary>
</indexterm>
<function>pg_current_wal_lsn</function> ()
<returnvalue>pg_lsn</returnvalue>
</para>
<para>
Returns the current write-ahead log write location (see notes below).
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_start_backup</primary>
</indexterm>
<function>pg_start_backup</function> (
<parameter>label</parameter> <type>text</type>
<optional>, <parameter>fast</parameter> <type>boolean</type>
<optional>, <parameter>exclusive</parameter> <type>boolean</type>
</optional></optional> )
<returnvalue>pg_lsn</returnvalue>
</para>
<para>
Prepares the server to begin an on-line backup. The only required
parameter is an arbitrary user-defined label for the backup.
(Typically this would be the name under which the backup dump file
will be stored.)
If the optional second parameter is given as <literal>true</literal>,
it specifies executing <function>pg_start_backup</function> as quickly
as possible. This forces an immediate checkpoint which will cause a
spike in I/O operations, slowing any concurrently executing queries.
The optional third parameter specifies whether to perform an exclusive
or non-exclusive backup (default is exclusive).
</para>
<para>
When used in exclusive mode, this function writes a backup label file
(<filename>backup_label</filename>) and, if there are any links in
the <filename>pg_tblspc/</filename> directory, a tablespace map file
(<filename>tablespace_map</filename>) into the database cluster's data
directory, then performs a checkpoint, and then returns the backup's
starting write-ahead log location. (The user can ignore this
result value, but it is provided in case it is useful.) When used in
non-exclusive mode, the contents of these files are instead returned
by the <function>pg_stop_backup</function> function, and should be
copied to the backup area by the user.
</para>
<para>
This function is restricted to superusers by default, but other users
can be granted EXECUTE to run the function.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_stop_backup</primary>
</indexterm>
<function>pg_stop_backup</function> (
<parameter>exclusive</parameter> <type>boolean</type>
<optional>, <parameter>wait_for_archive</parameter> <type>boolean</type>
</optional> )
<returnvalue>setof record</returnvalue>
( <parameter>lsn</parameter> <type>pg_lsn</type>,
<parameter>labelfile</parameter> <type>text</type>,
<parameter>spcmapfile</parameter> <type>text</type> )
</para>
<para>
Finishes performing an exclusive or non-exclusive on-line backup.
The <parameter>exclusive</parameter> parameter must match the
previous <function>pg_start_backup</function> call.
In an exclusive backup, <function>pg_stop_backup</function> removes
the backup label file and, if it exists, the tablespace map file
created by <function>pg_start_backup</function>. In a non-exclusive
backup, the desired contents of these files are returned as part of
the result of the function, and should be written to files in the
backup area (not in the data directory).
</para>
<para>
There is an optional second parameter of type <type>boolean</type>.
If false, the function will return immediately after the backup is
completed, without waiting for WAL to be archived. This behavior is
only useful with backup software that independently monitors WAL
archiving. Otherwise, WAL required to make the backup consistent might
be missing and make the backup useless. By default or when this
parameter is true, <function>pg_stop_backup</function> will wait for
WAL to be archived when archiving is enabled. (On a standby, this
means that it will wait only when <varname>archive_mode</varname> =
<literal>always</literal>. If write activity on the primary is low,
it may be useful to run <function>pg_switch_wal</function> on the
primary in order to trigger an immediate segment switch.)
</para>
<para>
When executed on a primary, this function also creates a backup
history file in the write-ahead log archive area. The history file
includes the label given to <function>pg_start_backup</function>, the
starting and ending write-ahead log locations for the backup, and the
starting and ending times of the backup. After recording the ending
location, the current write-ahead log insertion point is automatically
advanced to the next write-ahead log file, so that the ending
write-ahead log file can be archived immediately to complete the
backup.
</para>
<para>
The result of the function is a single record.
The <parameter>lsn</parameter> column holds the backup's ending
write-ahead log location (which again can be ignored). The second and
third columns are <literal>NULL</literal> when ending an exclusive
backup; after a non-exclusive backup they hold the desired contents of
the label and tablespace map files.
</para>
<para>
This function is restricted to superusers by default, but other users
can be granted EXECUTE to run the function.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<function>pg_stop_backup</function> ()
<returnvalue>pg_lsn</returnvalue>
</para>
<para>
Finishes performing an exclusive on-line backup. This simplified
version is equivalent to <literal>pg_stop_backup(true,
true)</literal>, except that it only returns the <type>pg_lsn</type>
result.
</para>
<para>
This function is restricted to superusers by default, but other users
can be granted EXECUTE to run the function.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_is_in_backup</primary>
</indexterm>
<function>pg_is_in_backup</function> ()
<returnvalue>boolean</returnvalue>
</para>
<para>
Returns true if an on-line exclusive backup is in progress.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_backup_start_time</primary>
</indexterm>
<function>pg_backup_start_time</function> ()
<returnvalue>timestamp with time zone</returnvalue>
</para>
<para>
Returns the start time of the current on-line exclusive backup if one
is in progress, otherwise <literal>NULL</literal>.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_switch_wal</primary>
</indexterm>
<function>pg_switch_wal</function> ()
<returnvalue>pg_lsn</returnvalue>
</para>
<para>
Forces the server to switch to a new write-ahead log file, which
allows the current file to be archived (assuming you are using
continuous archiving). The result is the ending write-ahead log
location plus 1 within the just-completed write-ahead log file. If
there has been no write-ahead log activity since the last write-ahead
log switch, <function>pg_switch_wal</function> does nothing and
returns the start location of the write-ahead log file currently in
use.
</para>
<para>
This function is restricted to superusers by default, but other users
can be granted EXECUTE to run the function.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_walfile_name</primary>
</indexterm>
<function>pg_walfile_name</function> ( <parameter>lsn</parameter> <type>pg_lsn</type> )
<returnvalue>text</returnvalue>
</para>
<para>
Converts a write-ahead log location to the name of the WAL file
holding that location.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_walfile_name_offset</primary>
</indexterm>
<function>pg_walfile_name_offset</function> ( <parameter>lsn</parameter> <type>pg_lsn</type> )
<returnvalue>record</returnvalue>
( <parameter>file_name</parameter> <type>text</type>,
<parameter>file_offset</parameter> <type>integer</type> )
</para>
<para>
Converts a write-ahead log location to a WAL file name and byte offset
within that file.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_wal_lsn_diff</primary>
</indexterm>
<function>pg_wal_lsn_diff</function> ( <parameter>lsn1</parameter> <type>pg_lsn</type>, <parameter>lsn2</parameter> <type>pg_lsn</type> )
<returnvalue>numeric</returnvalue>
</para>
<para>
Calculates the difference in bytes (<parameter>lsn1</parameter> - <parameter>lsn2</parameter>) between two write-ahead log
locations. This can be used
with <structname>pg_stat_replication</structname> or some of the
functions shown in <xref linkend="functions-admin-backup-table"/> to
get the replication lag.
</para></entry>
</row>
</tbody>
</tgroup>
</table>
<para>
<function>pg_current_wal_lsn</function> displays the current write-ahead
log write location in the same format used by the above functions.
Similarly, <function>pg_current_wal_insert_lsn</function> displays the
current write-ahead log insertion location
and <function>pg_current_wal_flush_lsn</function> displays the current
write-ahead log flush location. The insertion location is
the <quote>logical</quote> end of the write-ahead log at any instant,
while the write location is the end of what has actually been written out
from the server's internal buffers, and the flush location is the last
location known to be written to durable storage. The write location is the
end of what can be examined from outside the server, and is usually what
you want if you are interested in archiving partially-complete write-ahead
log files. The insertion and flush locations are made available primarily
for server debugging purposes. These are all read-only operations and do
not require superuser permissions.
</para>
<para>
You can use <function>pg_walfile_name_offset</function> to extract the
corresponding write-ahead log file name and byte offset from
a <type>pg_lsn</type> value. For example:
<programlisting>
postgres=# SELECT * FROM pg_walfile_name_offset(pg_stop_backup());
file_name | file_offset
--------------------------+-------------
00000001000000000000000D | 4039624
(1 row)
</programlisting>
Similarly, <function>pg_walfile_name</function> extracts just the write-ahead log file name.
When the given write-ahead log location is exactly at a write-ahead log file boundary, both
these functions return the name of the preceding write-ahead log file.
This is usually the desired behavior for managing write-ahead log archiving
behavior, since the preceding file is the last one that currently
needs to be archived.
</para>
</sect2>
<sect2 id="functions-recovery-control">
<title>Recovery Control Functions</title>
<para>
The functions shown in <xref
linkend="functions-recovery-info-table"/> provide information
about the current status of a standby server.
These functions may be executed both during recovery and in normal running.
</para>
<table id="functions-recovery-info-table">
<title>Recovery Information Functions</title>
<tgroup cols="1">
<thead>
<row>
<entry role="func_table_entry"><para role="func_signature">
Function
</para>
<para>
Description
</para></entry>
</row>
</thead>
<tbody>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_is_in_recovery</primary>
</indexterm>
<function>pg_is_in_recovery</function> ()
<returnvalue>boolean</returnvalue>
</para>
<para>
Returns true if recovery is still in progress.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_last_wal_receive_lsn</primary>
</indexterm>
<function>pg_last_wal_receive_lsn</function> ()
<returnvalue>pg_lsn</returnvalue>
</para>
<para>
Returns the last write-ahead log location that has been received and
synced to disk by streaming replication. While streaming replication
is in progress this will increase monotonically. If recovery has
completed then this will remain static at the location of the last WAL
record received and synced to disk during recovery. If streaming
replication is disabled, or if it has not yet started, the function
returns <literal>NULL</literal>.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_last_wal_replay_lsn</primary>
</indexterm>
<function>pg_last_wal_replay_lsn</function> ()
<returnvalue>pg_lsn</returnvalue>
</para>
<para>
Returns the last write-ahead log location that has been replayed
during recovery. If recovery is still in progress this will increase
monotonically. If recovery has completed then this will remain
static at the location of the last WAL record applied during recovery.
When the server has been started normally without recovery, the
function returns <literal>NULL</literal>.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_last_xact_replay_timestamp</primary>
</indexterm>
<function>pg_last_xact_replay_timestamp</function> ()
<returnvalue>timestamp with time zone</returnvalue>
</para>
<para>
Returns the time stamp of the last transaction replayed during
recovery. This is the time at which the commit or abort WAL record
for that transaction was generated on the primary. If no transactions
have been replayed during recovery, the function
returns <literal>NULL</literal>. Otherwise, if recovery is still in
progress this will increase monotonically. If recovery has completed
then this will remain static at the time of the last transaction
applied during recovery. When the server has been started normally
without recovery, the function returns <literal>NULL</literal>.
</para></entry>
</row>
</tbody>
</tgroup>
</table>
<para>
The functions shown in <xref
linkend="functions-recovery-control-table"/> control the progress of recovery.
These functions may be executed only during recovery.
</para>
<table id="functions-recovery-control-table">
<title>Recovery Control Functions</title>
<tgroup cols="1">
<thead>
<row>
<entry role="func_table_entry"><para role="func_signature">
Function
</para>
<para>
Description
</para></entry>
</row>
</thead>
<tbody>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_is_wal_replay_paused</primary>
</indexterm>
<function>pg_is_wal_replay_paused</function> ()
<returnvalue>boolean</returnvalue>
</para>
<para>
Returns true if recovery pause is requested.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_get_wal_replay_pause_state</primary>
</indexterm>
<function>pg_get_wal_replay_pause_state</function> ()
<returnvalue>text</returnvalue>
</para>
<para>
Returns recovery pause state. The return values are <literal>
not paused</literal> if pause is not requested, <literal>
pause requested</literal> if pause is requested but recovery is
not yet paused, and <literal>paused</literal> if the recovery is
actually paused.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_promote</primary>
</indexterm>
<function>pg_promote</function> ( <parameter>wait</parameter> <type>boolean</type> <literal>DEFAULT</literal> <literal>true</literal>, <parameter>wait_seconds</parameter> <type>integer</type> <literal>DEFAULT</literal> <literal>60</literal> )
<returnvalue>boolean</returnvalue>
</para>
<para>
Promotes a standby server to primary status.
With <parameter>wait</parameter> set to <literal>true</literal> (the
default), the function waits until promotion is completed
or <parameter>wait_seconds</parameter> seconds have passed, and
returns <literal>true</literal> if promotion is successful
and <literal>false</literal> otherwise.
If <parameter>wait</parameter> is set to <literal>false</literal>, the
function returns <literal>true</literal> immediately after sending a
<literal>SIGUSR1</literal> signal to the postmaster to trigger
promotion.
</para>
<para>
This function is restricted to superusers by default, but other users
can be granted EXECUTE to run the function.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_wal_replay_pause</primary>
</indexterm>
<function>pg_wal_replay_pause</function> ()
<returnvalue>void</returnvalue>
</para>
<para>
Request to pause recovery. A request doesn't mean that recovery stops
right away. If you want a guarantee that recovery is actually paused,
you need to check for the recovery pause state returned by
<function>pg_get_wal_replay_pause_state()</function>. Note that
<function>pg_is_wal_replay_paused()</function> returns whether a request
is made. While recovery is paused, no further database changes are applied.
If hot standby is active, all new queries will see the same consistent
snapshot of the database, and no further query conflicts will be generated
until recovery is resumed.
</para>
<para>
This function is restricted to superusers by default, but other users
can be granted EXECUTE to run the function.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_wal_replay_resume</primary>
</indexterm>
<function>pg_wal_replay_resume</function> ()
<returnvalue>void</returnvalue>
</para>
<para>
Restarts recovery if it was paused.
</para>
<para>
This function is restricted to superusers by default, but other users
can be granted EXECUTE to run the function.
</para></entry>
</row>
</tbody>
</tgroup>
</table>
<para>
<function>pg_wal_replay_pause</function> and
<function>pg_wal_replay_resume</function> cannot be executed while
a promotion is ongoing. If a promotion is triggered while recovery
is paused, the paused state ends and promotion continues.
</para>
<para>
If streaming replication is disabled, the paused state may continue
indefinitely without a problem. If streaming replication is in
progress then WAL records will continue to be received, which will
eventually fill available disk space, depending upon the duration of
the pause, the rate of WAL generation and available disk space.
</para>
</sect2>
<sect2 id="functions-snapshot-synchronization">
<title>Snapshot Synchronization Functions</title>
<para>
<productname>PostgreSQL</productname> allows database sessions to synchronize their
snapshots. A <firstterm>snapshot</firstterm> determines which data is visible to the
transaction that is using the snapshot. Synchronized snapshots are
necessary when two or more sessions need to see identical content in the
database. If two sessions just start their transactions independently,
there is always a possibility that some third transaction commits
between the executions of the two <command>START TRANSACTION</command> commands,
so that one session sees the effects of that transaction and the other
does not.
</para>
<para>
To solve this problem, <productname>PostgreSQL</productname> allows a transaction to
<firstterm>export</firstterm> the snapshot it is using. As long as the exporting
transaction remains open, other transactions can <firstterm>import</firstterm> its
snapshot, and thereby be guaranteed that they see exactly the same view
of the database that the first transaction sees. But note that any
database changes made by any one of these transactions remain invisible
to the other transactions, as is usual for changes made by uncommitted
transactions. So the transactions are synchronized with respect to
pre-existing data, but act normally for changes they make themselves.
</para>
<para>
Snapshots are exported with the <function>pg_export_snapshot</function> function,
shown in <xref linkend="functions-snapshot-synchronization-table"/>, and
imported with the <xref linkend="sql-set-transaction"/> command.
</para>
<table id="functions-snapshot-synchronization-table">
<title>Snapshot Synchronization Functions</title>
<tgroup cols="1">
<thead>
<row>
<entry role="func_table_entry"><para role="func_signature">
Function
</para>
<para>
Description
</para></entry>
</row>
</thead>
<tbody>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_export_snapshot</primary>
</indexterm>
<function>pg_export_snapshot</function> ()
<returnvalue>text</returnvalue>
</para>
<para>
Saves the transaction's current snapshot and returns
a <type>text</type> string identifying the snapshot. This string must
be passed (outside the database) to clients that want to import the
snapshot. The snapshot is available for import only until the end of
the transaction that exported it.
</para>
<para>
A transaction can export more than one snapshot, if needed. Note that
doing so is only useful in <literal>READ COMMITTED</literal>
transactions, since in <literal>REPEATABLE READ</literal> and higher
isolation levels, transactions use the same snapshot throughout their
lifetime. Once a transaction has exported any snapshots, it cannot be
prepared with <xref linkend="sql-prepare-transaction"/>.
</para></entry>
</row>
</tbody>
</tgroup>
</table>
</sect2>
<sect2 id="functions-replication">
<title>Replication Management Functions</title>
<para>
The functions shown
in <xref linkend="functions-replication-table"/> are for
controlling and interacting with replication features.
See <xref linkend="streaming-replication"/>,
<xref linkend="streaming-replication-slots"/>, and
<xref linkend="replication-origins"/>
for information about the underlying features.
Use of functions for replication origin is only allowed to the
superuser by default, but may be allowed to other users by using the
<literal>GRANT</literal> command.
Use of functions for replication slots is restricted to superusers
and users having <literal>REPLICATION</literal> privilege.
</para>
<para>
Many of these functions have equivalent commands in the replication
protocol; see <xref linkend="protocol-replication"/>.
</para>
<para>
The functions described in
<xref linkend="functions-admin-backup"/>,
<xref linkend="functions-recovery-control"/>, and
<xref linkend="functions-snapshot-synchronization"/>
are also relevant for replication.
</para>
<table id="functions-replication-table">
<title>Replication Management Functions</title>
<tgroup cols="1">
<thead>
<row>
<entry role="func_table_entry"><para role="func_signature">
Function
</para>
<para>
Description
</para></entry>
</row>
</thead>
<tbody>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_create_physical_replication_slot</primary>
</indexterm>
<function>pg_create_physical_replication_slot</function> ( <parameter>slot_name</parameter> <type>name</type> <optional>, <parameter>immediately_reserve</parameter> <type>boolean</type>, <parameter>temporary</parameter> <type>boolean</type> </optional> )
<returnvalue>record</returnvalue>
( <parameter>slot_name</parameter> <type>name</type>,
<parameter>lsn</parameter> <type>pg_lsn</type> )
</para>
<para>
Creates a new physical replication slot named
<parameter>slot_name</parameter>. The optional second parameter,
when <literal>true</literal>, specifies that the <acronym>LSN</acronym> for this
replication slot be reserved immediately; otherwise
the <acronym>LSN</acronym> is reserved on first connection from a streaming
replication client. Streaming changes from a physical slot is only
possible with the streaming-replication protocol —
see <xref linkend="protocol-replication"/>. The optional third
parameter, <parameter>temporary</parameter>, when set to true, specifies that
the slot should not be permanently stored to disk and is only meant
for use by the current session. Temporary slots are also
released upon any error. This function corresponds
to the replication protocol command <literal>CREATE_REPLICATION_SLOT
... PHYSICAL</literal>.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_drop_replication_slot</primary>
</indexterm>
<function>pg_drop_replication_slot</function> ( <parameter>slot_name</parameter> <type>name</type> )
<returnvalue>void</returnvalue>
</para>
<para>
Drops the physical or logical replication slot
named <parameter>slot_name</parameter>. Same as replication protocol
command <literal>DROP_REPLICATION_SLOT</literal>. For logical slots, this must
be called while connected to the same database the slot was created on.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_create_logical_replication_slot</primary>
</indexterm>
<function>pg_create_logical_replication_slot</function> ( <parameter>slot_name</parameter> <type>name</type>, <parameter>plugin</parameter> <type>name</type> <optional>, <parameter>temporary</parameter> <type>boolean</type>, <parameter>two_phase</parameter> <type>boolean</type> </optional> )
<returnvalue>record</returnvalue>
( <parameter>slot_name</parameter> <type>name</type>,
<parameter>lsn</parameter> <type>pg_lsn</type> )
</para>
<para>
Creates a new logical (decoding) replication slot named
<parameter>slot_name</parameter> using the output plugin
<parameter>plugin</parameter>. The optional third
parameter, <parameter>temporary</parameter>, when set to true, specifies that
the slot should not be permanently stored to disk and is only meant
for use by the current session. Temporary slots are also
released upon any error. The optional fourth parameter,
<parameter>two_phase</parameter>, when set to true, specifies
that the decoding of prepared transactions is enabled for this
slot. A call to this function has the same effect as the replication
protocol command <literal>CREATE_REPLICATION_SLOT ... LOGICAL</literal>.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_copy_physical_replication_slot</primary>
</indexterm>
<function>pg_copy_physical_replication_slot</function> ( <parameter>src_slot_name</parameter> <type>name</type>, <parameter>dst_slot_name</parameter> <type>name</type> <optional>, <parameter>temporary</parameter> <type>boolean</type> </optional> )
<returnvalue>record</returnvalue>
( <parameter>slot_name</parameter> <type>name</type>,
<parameter>lsn</parameter> <type>pg_lsn</type> )
</para>
<para>
Copies an existing physical replication slot named <parameter>src_slot_name</parameter>
to a physical replication slot named <parameter>dst_slot_name</parameter>.
The copied physical slot starts to reserve WAL from the same <acronym>LSN</acronym> as the
source slot.
<parameter>temporary</parameter> is optional. If <parameter>temporary</parameter>
is omitted, the same value as the source slot is used.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_copy_logical_replication_slot</primary>
</indexterm>
<function>pg_copy_logical_replication_slot</function> ( <parameter>src_slot_name</parameter> <type>name</type>, <parameter>dst_slot_name</parameter> <type>name</type> <optional>, <parameter>temporary</parameter> <type>boolean</type> <optional>, <parameter>plugin</parameter> <type>name</type> </optional></optional> )
<returnvalue>record</returnvalue>
( <parameter>slot_name</parameter> <type>name</type>,
<parameter>lsn</parameter> <type>pg_lsn</type> )
</para>
<para>
Copies an existing logical replication slot
named <parameter>src_slot_name</parameter> to a logical replication
slot named <parameter>dst_slot_name</parameter>, optionally changing
the output plugin and persistence. The copied logical slot starts
from the same <acronym>LSN</acronym> as the source logical slot. Both
<parameter>temporary</parameter> and <parameter>plugin</parameter> are
optional; if they are omitted, the values of the source slot are used.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_logical_slot_get_changes</primary>
</indexterm>
<function>pg_logical_slot_get_changes</function> ( <parameter>slot_name</parameter> <type>name</type>, <parameter>upto_lsn</parameter> <type>pg_lsn</type>, <parameter>upto_nchanges</parameter> <type>integer</type>, <literal>VARIADIC</literal> <parameter>options</parameter> <type>text[]</type> )
<returnvalue>setof record</returnvalue>
( <parameter>lsn</parameter> <type>pg_lsn</type>,
<parameter>xid</parameter> <type>xid</type>,
<parameter>data</parameter> <type>text</type> )
</para>
<para>
Returns changes in the slot <parameter>slot_name</parameter>, starting
from the point from which changes have been consumed last. If
<parameter>upto_lsn</parameter>
and <parameter>upto_nchanges</parameter> are NULL,
logical decoding will continue until end of WAL. If
<parameter>upto_lsn</parameter> is non-NULL, decoding will include only
those transactions which commit prior to the specified LSN. If
<parameter>upto_nchanges</parameter> is non-NULL, decoding will
stop when the number of rows produced by decoding exceeds
the specified value. Note, however, that the actual number of
rows returned may be larger, since this limit is only checked after
adding the rows produced when decoding each new transaction commit.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_logical_slot_peek_changes</primary>
</indexterm>
<function>pg_logical_slot_peek_changes</function> ( <parameter>slot_name</parameter> <type>name</type>, <parameter>upto_lsn</parameter> <type>pg_lsn</type>, <parameter>upto_nchanges</parameter> <type>integer</type>, <literal>VARIADIC</literal> <parameter>options</parameter> <type>text[]</type> )
<returnvalue>setof record</returnvalue>
( <parameter>lsn</parameter> <type>pg_lsn</type>,
<parameter>xid</parameter> <type>xid</type>,
<parameter>data</parameter> <type>text</type> )
</para>
<para>
Behaves just like
the <function>pg_logical_slot_get_changes()</function> function,
except that changes are not consumed; that is, they will be returned
again on future calls.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_logical_slot_get_binary_changes</primary>
</indexterm>
<function>pg_logical_slot_get_binary_changes</function> ( <parameter>slot_name</parameter> <type>name</type>, <parameter>upto_lsn</parameter> <type>pg_lsn</type>, <parameter>upto_nchanges</parameter> <type>integer</type>, <literal>VARIADIC</literal> <parameter>options</parameter> <type>text[]</type> )
<returnvalue>setof record</returnvalue>
( <parameter>lsn</parameter> <type>pg_lsn</type>,
<parameter>xid</parameter> <type>xid</type>,
<parameter>data</parameter> <type>bytea</type> )
</para>
<para>
Behaves just like
the <function>pg_logical_slot_get_changes()</function> function,
except that changes are returned as <type>bytea</type>.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_logical_slot_peek_binary_changes</primary>
</indexterm>
<function>pg_logical_slot_peek_binary_changes</function> ( <parameter>slot_name</parameter> <type>name</type>, <parameter>upto_lsn</parameter> <type>pg_lsn</type>, <parameter>upto_nchanges</parameter> <type>integer</type>, <literal>VARIADIC</literal> <parameter>options</parameter> <type>text[]</type> )
<returnvalue>setof record</returnvalue>
( <parameter>lsn</parameter> <type>pg_lsn</type>,
<parameter>xid</parameter> <type>xid</type>,
<parameter>data</parameter> <type>bytea</type> )
</para>
<para>
Behaves just like
the <function>pg_logical_slot_peek_changes()</function> function,
except that changes are returned as <type>bytea</type>.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_replication_slot_advance</primary>
</indexterm>
<function>pg_replication_slot_advance</function> ( <parameter>slot_name</parameter> <type>name</type>, <parameter>upto_lsn</parameter> <type>pg_lsn</type> )
<returnvalue>record</returnvalue>
( <parameter>slot_name</parameter> <type>name</type>,
<parameter>end_lsn</parameter> <type>pg_lsn</type> )
</para>
<para>
Advances the current confirmed position of a replication slot named
<parameter>slot_name</parameter>. The slot will not be moved backwards,
and it will not be moved beyond the current insert location. Returns
the name of the slot and the actual position that it was advanced to.
The updated slot position information is written out at the next
checkpoint if any advancing is done. So in the event of a crash, the
slot may return to an earlier position.
</para></entry>
</row>
<row>
<entry id="pg-replication-origin-create" role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_replication_origin_create</primary>
</indexterm>
<function>pg_replication_origin_create</function> ( <parameter>node_name</parameter> <type>text</type> )
<returnvalue>oid</returnvalue>
</para>
<para>
Creates a replication origin with the given external
name, and returns the internal ID assigned to it.
</para></entry>
</row>
<row>
<entry id="pg-replication-origin-drop" role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_replication_origin_drop</primary>
</indexterm>
<function>pg_replication_origin_drop</function> ( <parameter>node_name</parameter> <type>text</type> )
<returnvalue>void</returnvalue>
</para>
<para>
Deletes a previously-created replication origin, including any
associated replay progress.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_replication_origin_oid</primary>
</indexterm>
<function>pg_replication_origin_oid</function> ( <parameter>node_name</parameter> <type>text</type> )
<returnvalue>oid</returnvalue>
</para>
<para>
Looks up a replication origin by name and returns the internal ID. If
no such replication origin is found an error is thrown.
</para></entry>
</row>
<row>
<entry id="pg-replication-origin-session-setup" role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_replication_origin_session_setup</primary>
</indexterm>
<function>pg_replication_origin_session_setup</function> ( <parameter>node_name</parameter> <type>text</type> )
<returnvalue>void</returnvalue>
</para>
<para>
Marks the current session as replaying from the given
origin, allowing replay progress to be tracked.
Can only be used if no origin is currently selected.
Use <function>pg_replication_origin_session_reset</function> to undo.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_replication_origin_session_reset</primary>
</indexterm>
<function>pg_replication_origin_session_reset</function> ()
<returnvalue>void</returnvalue>
</para>
<para>
Cancels the effects
of <function>pg_replication_origin_session_setup()</function>.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_replication_origin_session_is_setup</primary>
</indexterm>
<function>pg_replication_origin_session_is_setup</function> ()
<returnvalue>boolean</returnvalue>
</para>
<para>
Returns true if a replication origin has been selected in the
current session.
</para></entry>
</row>
<row>
<entry id="pg-replication-origin-session-progress" role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_replication_origin_session_progress</primary>
</indexterm>
<function>pg_replication_origin_session_progress</function> ( <parameter>flush</parameter> <type>boolean</type> )
<returnvalue>pg_lsn</returnvalue>
</para>
<para>
Returns the replay location for the replication origin selected in
the current session. The parameter <parameter>flush</parameter>
determines whether the corresponding local transaction will be
guaranteed to have been flushed to disk or not.
</para></entry>
</row>
<row>
<entry id="pg-replication-origin-xact-setup" role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_replication_origin_xact_setup</primary>
</indexterm>
<function>pg_replication_origin_xact_setup</function> ( <parameter>origin_lsn</parameter> <type>pg_lsn</type>, <parameter>origin_timestamp</parameter> <type>timestamp with time zone</type> )
<returnvalue>void</returnvalue>
</para>
<para>
Marks the current transaction as replaying a transaction that has
committed at the given <acronym>LSN</acronym> and timestamp. Can
only be called when a replication origin has been selected
using <function>pg_replication_origin_session_setup</function>.
</para></entry>
</row>
<row>
<entry id="pg-replication-origin-xact-reset" role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_replication_origin_xact_reset</primary>
</indexterm>
<function>pg_replication_origin_xact_reset</function> ()
<returnvalue>void</returnvalue>
</para>
<para>
Cancels the effects of
<function>pg_replication_origin_xact_setup()</function>.
</para></entry>
</row>
<row>
<entry id="pg-replication-origin-advance" role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_replication_origin_advance</primary>
</indexterm>
<function>pg_replication_origin_advance</function> ( <parameter>node_name</parameter> <type>text</type>, <parameter>lsn</parameter> <type>pg_lsn</type> )
<returnvalue>void</returnvalue>
</para>
<para>
Sets replication progress for the given node to the given
location. This is primarily useful for setting up the initial
location, or setting a new location after configuration changes and
similar. Be aware that careless use of this function can lead to
inconsistently replicated data.
</para></entry>
</row>
<row>
<entry id="pg-replication-origin-progress" role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_replication_origin_progress</primary>
</indexterm>
<function>pg_replication_origin_progress</function> ( <parameter>node_name</parameter> <type>text</type>, <parameter>flush</parameter> <type>boolean</type> )
<returnvalue>pg_lsn</returnvalue>
</para>
<para>
Returns the replay location for the given replication origin. The
parameter <parameter>flush</parameter> determines whether the
corresponding local transaction will be guaranteed to have been
flushed to disk or not.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_logical_emit_message</primary>
</indexterm>
<function>pg_logical_emit_message</function> ( <parameter>transactional</parameter> <type>boolean</type>, <parameter>prefix</parameter> <type>text</type>, <parameter>content</parameter> <type>text</type> )
<returnvalue>pg_lsn</returnvalue>
</para>
<para role="func_signature">
<function>pg_logical_emit_message</function> ( <parameter>transactional</parameter> <type>boolean</type>, <parameter>prefix</parameter> <type>text</type>, <parameter>content</parameter> <type>bytea</type> )
<returnvalue>pg_lsn</returnvalue>
</para>
<para>
Emits a logical decoding message. This can be used to pass generic
messages to logical decoding plugins through
WAL. The <parameter>transactional</parameter> parameter specifies if
the message should be part of the current transaction, or if it should
be written immediately and decoded as soon as the logical decoder
reads the record. The <parameter>prefix</parameter> parameter is a
textual prefix that can be used by logical decoding plugins to easily
recognize messages that are interesting for them.
The <parameter>content</parameter> parameter is the content of the
message, given either in text or binary form.
</para></entry>
</row>
</tbody>
</tgroup>
</table>
</sect2>
<sect2 id="functions-admin-dbobject">
<title>Database Object Management Functions</title>
<para>
The functions shown in <xref linkend="functions-admin-dbsize"/> calculate
the disk space usage of database objects, or assist in presentation
or understanding of usage results. <literal>bigint</literal> results
are measured in bytes. If an OID that does
not represent an existing object is passed to one of these
functions, <literal>NULL</literal> is returned.
</para>
<table id="functions-admin-dbsize">
<title>Database Object Size Functions</title>
<tgroup cols="1">
<thead>
<row>
<entry role="func_table_entry"><para role="func_signature">
Function
</para>
<para>
Description
</para></entry>
</row>
</thead>
<tbody>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_column_size</primary>
</indexterm>
<function>pg_column_size</function> ( <type>"any"</type> )
<returnvalue>integer</returnvalue>
</para>
<para>
Shows the number of bytes used to store any individual data value. If
applied directly to a table column value, this reflects any
compression that was done.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_column_compression</primary>
</indexterm>
<function>pg_column_compression</function> ( <type>"any"</type> )
<returnvalue>text</returnvalue>
</para>
<para>
Shows the compression algorithm that was used to compress
an individual variable-length value. Returns <literal>NULL</literal>
if the value is not compressed.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_database_size</primary>
</indexterm>
<function>pg_database_size</function> ( <type>name</type> )
<returnvalue>bigint</returnvalue>
</para>
<para role="func_signature">
<function>pg_database_size</function> ( <type>oid</type> )
<returnvalue>bigint</returnvalue>
</para>
<para>
Computes the total disk space used by the database with the specified
name or OID. To use this function, you must
have <literal>CONNECT</literal> privilege on the specified database
(which is granted by default) or be a member of
the <literal>pg_read_all_stats</literal> role.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_indexes_size</primary>
</indexterm>
<function>pg_indexes_size</function> ( <type>regclass</type> )
<returnvalue>bigint</returnvalue>
</para>
<para>
Computes the total disk space used by indexes attached to the
specified table.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_relation_size</primary>
</indexterm>
<function>pg_relation_size</function> ( <parameter>relation</parameter> <type>regclass</type> <optional>, <parameter>fork</parameter> <type>text</type> </optional> )
<returnvalue>bigint</returnvalue>
</para>
<para>
Computes the disk space used by one <quote>fork</quote> of the
specified relation. (Note that for most purposes it is more
convenient to use the higher-level
functions <function>pg_total_relation_size</function>
or <function>pg_table_size</function>, which sum the sizes of all
forks.) With one argument, this returns the size of the main data
fork of the relation. The second argument can be provided to specify
which fork to examine:
<itemizedlist spacing="compact">
<listitem>
<para>
<literal>main</literal> returns the size of the main
data fork of the relation.
</para>
</listitem>
<listitem>
<para>
<literal>fsm</literal> returns the size of the Free Space Map
(see <xref linkend="storage-fsm"/>) associated with the relation.
</para>
</listitem>
<listitem>
<para>
<literal>vm</literal> returns the size of the Visibility Map
(see <xref linkend="storage-vm"/>) associated with the relation.
</para>
</listitem>
<listitem>
<para>
<literal>init</literal> returns the size of the initialization
fork, if any, associated with the relation.
</para>
</listitem>
</itemizedlist>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_size_bytes</primary>
</indexterm>
<function>pg_size_bytes</function> ( <type>text</type> )
<returnvalue>bigint</returnvalue>
</para>
<para>
Converts a size in human-readable format (as returned
by <function>pg_size_pretty</function>) into bytes.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_size_pretty</primary>
</indexterm>
<function>pg_size_pretty</function> ( <type>bigint</type> )
<returnvalue>text</returnvalue>
</para>
<para role="func_signature">
<function>pg_size_pretty</function> ( <type>numeric</type> )
<returnvalue>text</returnvalue>
</para>
<para>
Converts a size in bytes into a more easily human-readable format with
size units (bytes, kB, MB, GB or TB as appropriate). Note that the
units are powers of 2 rather than powers of 10, so 1kB is 1024 bytes,
1MB is 1024<superscript>2</superscript> = 1048576 bytes, and so on.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_table_size</primary>
</indexterm>
<function>pg_table_size</function> ( <type>regclass</type> )
<returnvalue>bigint</returnvalue>
</para>
<para>
Computes the disk space used by the specified table, excluding indexes
(but including its TOAST table if any, free space map, and visibility
map).
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_tablespace_size</primary>
</indexterm>
<function>pg_tablespace_size</function> ( <type>name</type> )
<returnvalue>bigint</returnvalue>
</para>
<para role="func_signature">
<function>pg_tablespace_size</function> ( <type>oid</type> )
<returnvalue>bigint</returnvalue>
</para>
<para>
Computes the total disk space used in the tablespace with the
specified name or OID. To use this function, you must
have <literal>CREATE</literal> privilege on the specified tablespace
or be a member of the <literal>pg_read_all_stats</literal> role,
unless it is the default tablespace for the current database.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_total_relation_size</primary>
</indexterm>
<function>pg_total_relation_size</function> ( <type>regclass</type> )
<returnvalue>bigint</returnvalue>
</para>
<para>
Computes the total disk space used by the specified table, including
all indexes and <acronym>TOAST</acronym> data. The result is
equivalent to <function>pg_table_size</function>
<literal>+</literal> <function>pg_indexes_size</function>.
</para></entry>
</row>
</tbody>
</tgroup>
</table>
<para>
The functions above that operate on tables or indexes accept a
<type>regclass</type> argument, which is simply the OID of the table or index
in the <structname>pg_class</structname> system catalog. You do not have to look up
the OID by hand, however, since the <type>regclass</type> data type's input
converter will do the work for you. See <xref linkend="datatype-oid"/>
for details.
</para>
<para>
The functions shown in <xref linkend="functions-admin-dblocation"/> assist
in identifying the specific disk files associated with database objects.
</para>
<table id="functions-admin-dblocation">
<title>Database Object Location Functions</title>
<tgroup cols="1">
<thead>
<row>
<entry role="func_table_entry"><para role="func_signature">
Function
</para>
<para>
Description
</para></entry>
</row>
</thead>
<tbody>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_relation_filenode</primary>
</indexterm>
<function>pg_relation_filenode</function> ( <parameter>relation</parameter> <type>regclass</type> )
<returnvalue>oid</returnvalue>
</para>
<para>
Returns the <quote>filenode</quote> number currently assigned to the
specified relation. The filenode is the base component of the file
name(s) used for the relation (see
<xref linkend="storage-file-layout"/> for more information).
For most relations the result is the same as
<structname>pg_class</structname>.<structfield>relfilenode</structfield>,
but for certain system catalogs <structfield>relfilenode</structfield>
is zero and this function must be used to get the correct value. The
function returns NULL if passed a relation that does not have storage,
such as a view.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_relation_filepath</primary>
</indexterm>
<function>pg_relation_filepath</function> ( <parameter>relation</parameter> <type>regclass</type> )
<returnvalue>text</returnvalue>
</para>
<para>
Returns the entire file path name (relative to the database cluster's
data directory, <varname>PGDATA</varname>) of the relation.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_filenode_relation</primary>
</indexterm>
<function>pg_filenode_relation</function> ( <parameter>tablespace</parameter> <type>oid</type>, <parameter>filenode</parameter> <type>oid</type> )
<returnvalue>regclass</returnvalue>
</para>
<para>
Returns a relation's OID given the tablespace OID and filenode it is
stored under. This is essentially the inverse mapping of
<function>pg_relation_filepath</function>. For a relation in the
database's default tablespace, the tablespace can be specified as zero.
Returns <literal>NULL</literal> if no relation in the current database
is associated with the given values.
</para></entry>
</row>
</tbody>
</tgroup>
</table>
<para>
<xref linkend="functions-admin-collation"/> lists functions used to manage
collations.
</para>
<table id="functions-admin-collation">
<title>Collation Management Functions</title>
<tgroup cols="1">
<thead>
<row>
<entry role="func_table_entry"><para role="func_signature">
Function
</para>
<para>
Description
</para></entry>
</row>
</thead>
<tbody>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_collation_actual_version</primary>
</indexterm>
<function>pg_collation_actual_version</function> ( <type>oid</type> )
<returnvalue>text</returnvalue>
</para>
<para>
Returns the actual version of the collation object as it is currently
installed in the operating system. If this is different from the
value in
<structname>pg_collation</structname>.<structfield>collversion</structfield>,
then objects depending on the collation might need to be rebuilt. See
also <xref linkend="sql-altercollation"/>.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_import_system_collations</primary>
</indexterm>
<function>pg_import_system_collations</function> ( <parameter>schema</parameter> <type>regnamespace</type> )
<returnvalue>integer</returnvalue>
</para>
<para>
Adds collations to the system
catalog <structname>pg_collation</structname> based on all the locales
it finds in the operating system. This is
what <command>initdb</command> uses; see
<xref linkend="collation-managing"/> for more details. If additional
locales are installed into the operating system later on, this
function can be run again to add collations for the new locales.
Locales that match existing entries
in <structname>pg_collation</structname> will be skipped. (But
collation objects based on locales that are no longer present in the
operating system are not removed by this function.)
The <parameter>schema</parameter> parameter would typically
be <literal>pg_catalog</literal>, but that is not a requirement; the
collations could be installed into some other schema as well. The
function returns the number of new collation objects it created.
Use of this function is restricted to superusers.
</para></entry>
</row>
</tbody>
</tgroup>
</table>
<para>
<xref linkend="functions-info-partition"/> lists functions that provide
information about the structure of partitioned tables.
</para>
<table id="functions-info-partition">
<title>Partitioning Information Functions</title>
<tgroup cols="1">
<thead>
<row>
<entry role="func_table_entry"><para role="func_signature">
Function
</para>
<para>
Description
</para></entry>
</row>
</thead>
<tbody>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_partition_tree</primary>
</indexterm>
<function>pg_partition_tree</function> ( <type>regclass</type> )
<returnvalue>setof record</returnvalue>
( <parameter>relid</parameter> <type>regclass</type>,
<parameter>parentrelid</parameter> <type>regclass</type>,
<parameter>isleaf</parameter> <type>boolean</type>,
<parameter>level</parameter> <type>integer</type> )
</para>
<para>
Lists the tables or indexes in the partition tree of the
given partitioned table or partitioned index, with one row for each
partition. Information provided includes the OID of the partition,
the OID of its immediate parent, a boolean value telling if the
partition is a leaf, and an integer telling its level in the hierarchy.
The level value is 0 for the input table or index, 1 for its
immediate child partitions, 2 for their partitions, and so on.
Returns no rows if the relation does not exist or is not a partition
or partitioned table.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_partition_ancestors</primary>
</indexterm>
<function>pg_partition_ancestors</function> ( <type>regclass</type> )
<returnvalue>setof regclass</returnvalue>
</para>
<para>
Lists the ancestor relations of the given partition,
including the relation itself. Returns no rows if the relation
does not exist or is not a partition or partitioned table.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_partition_root</primary>
</indexterm>
<function>pg_partition_root</function> ( <type>regclass</type> )
<returnvalue>regclass</returnvalue>
</para>
<para>
Returns the top-most parent of the partition tree to which the given
relation belongs. Returns <literal>NULL</literal> if the relation
does not exist or is not a partition or partitioned table.
</para></entry>
</row>
</tbody>
</tgroup>
</table>
<para>
For example, to check the total size of the data contained in a
partitioned table <structname>measurement</structname>, one could use the
following query:
<programlisting>
SELECT pg_size_pretty(sum(pg_relation_size(relid))) AS total_size
FROM pg_partition_tree('measurement');
</programlisting>
</para>
</sect2>
<sect2 id="functions-admin-index">
<title>Index Maintenance Functions</title>
<para>
<xref linkend="functions-admin-index-table"/> shows the functions
available for index maintenance tasks. (Note that these maintenance
tasks are normally done automatically by autovacuum; use of these
functions is only required in special cases.)
These functions cannot be executed during recovery.
Use of these functions is restricted to superusers and the owner
of the given index.
</para>
<table id="functions-admin-index-table">
<title>Index Maintenance Functions</title>
<tgroup cols="1">
<thead>
<row>
<entry role="func_table_entry"><para role="func_signature">
Function
</para>
<para>
Description
</para></entry>
</row>
</thead>
<tbody>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>brin_summarize_new_values</primary>
</indexterm>
<function>brin_summarize_new_values</function> ( <parameter>index</parameter> <type>regclass</type> )
<returnvalue>integer</returnvalue>
</para>
<para>
Scans the specified BRIN index to find page ranges in the base table
that are not currently summarized by the index; for any such range it
creates a new summary index tuple by scanning those table pages.
Returns the number of new page range summaries that were inserted
into the index.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>brin_summarize_range</primary>
</indexterm>
<function>brin_summarize_range</function> ( <parameter>index</parameter> <type>regclass</type>, <parameter>blockNumber</parameter> <type>bigint</type> )
<returnvalue>integer</returnvalue>
</para>
<para>
Summarizes the page range covering the given block, if not already
summarized. This is
like <function>brin_summarize_new_values</function> except that it
only processes the page range that covers the given table block number.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>brin_desummarize_range</primary>
</indexterm>
<function>brin_desummarize_range</function> ( <parameter>index</parameter> <type>regclass</type>, <parameter>blockNumber</parameter> <type>bigint</type> )
<returnvalue>void</returnvalue>
</para>
<para>
Removes the BRIN index tuple that summarizes the page range covering
the given table block, if there is one.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>gin_clean_pending_list</primary>
</indexterm>
<function>gin_clean_pending_list</function> ( <parameter>index</parameter> <type>regclass</type> )
<returnvalue>bigint</returnvalue>
</para>
<para>
Cleans up the <quote>pending</quote> list of the specified GIN index
by moving entries in it, in bulk, to the main GIN data structure.
Returns the number of pages removed from the pending list.
If the argument is a GIN index built with
the <literal>fastupdate</literal> option disabled, no cleanup happens
and the result is zero, because the index doesn't have a pending list.
See <xref linkend="gin-fast-update"/> and <xref linkend="gin-tips"/>
for details about the pending list and <literal>fastupdate</literal>
option.
</para></entry>
</row>
</tbody>
</tgroup>
</table>
</sect2>
<sect2 id="functions-admin-genfile">
<title>Generic File Access Functions</title>
<para>
The functions shown in <xref
linkend="functions-admin-genfile-table"/> provide native access to
files on the machine hosting the server. Only files within the
database cluster directory and the <varname>log_directory</varname> can be
accessed, unless the user is a superuser or is granted the role
<literal>pg_read_server_files</literal>. Use a relative path for files in
the cluster directory, and a path matching the <varname>log_directory</varname>
configuration setting for log files.
</para>
<para>
Note that granting users the EXECUTE privilege on
<function>pg_read_file()</function>, or related functions, allows them the
ability to read any file on the server that the database server process can
read; these functions bypass all in-database privilege checks. This means
that, for example, a user with such access is able to read the contents of
the <structname>pg_authid</structname> table where authentication
information is stored, as well as read any table data in the database.
Therefore, granting access to these functions should be carefully
considered.
</para>
<para>
Some of these functions take an optional <parameter>missing_ok</parameter>
parameter, which specifies the behavior when the file or directory does
not exist. If <literal>true</literal>, the function
returns <literal>NULL</literal> or an empty result set, as appropriate.
If <literal>false</literal>, an error is raised. The default
is <literal>false</literal>.
</para>
<table id="functions-admin-genfile-table">
<title>Generic File Access Functions</title>
<tgroup cols="1">
<thead>
<row>
<entry role="func_table_entry"><para role="func_signature">
Function
</para>
<para>
Description
</para></entry>
</row>
</thead>
<tbody>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_ls_dir</primary>
</indexterm>
<function>pg_ls_dir</function> ( <parameter>dirname</parameter> <type>text</type> <optional>, <parameter>missing_ok</parameter> <type>boolean</type>, <parameter>include_dot_dirs</parameter> <type>boolean</type> </optional> )
<returnvalue>setof text</returnvalue>
</para>
<para>
Returns the names of all files (and directories and other special
files) in the specified
directory. The <parameter>include_dot_dirs</parameter> parameter
indicates whether <quote>.</quote> and <quote>..</quote> are to be
included in the result set; the default is to exclude them. Including
them can be useful when <parameter>missing_ok</parameter>
is <literal>true</literal>, to distinguish an empty directory from a
non-existent directory.
</para>
<para>
This function is restricted to superusers by default, but other users
can be granted EXECUTE to run the function.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_ls_logdir</primary>
</indexterm>
<function>pg_ls_logdir</function> ()
<returnvalue>setof record</returnvalue>
( <parameter>name</parameter> <type>text</type>,
<parameter>size</parameter> <type>bigint</type>,
<parameter>modification</parameter> <type>timestamp with time zone</type> )
</para>
<para>
Returns the name, size, and last modification time (mtime) of each
ordinary file in the server's log directory. Filenames beginning with
a dot, directories, and other special files are excluded.
</para>
<para>
This function is restricted to superusers and members of
the <literal>pg_monitor</literal> role by default, but other users can
be granted EXECUTE to run the function.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_ls_waldir</primary>
</indexterm>
<function>pg_ls_waldir</function> ()
<returnvalue>setof record</returnvalue>
( <parameter>name</parameter> <type>text</type>,
<parameter>size</parameter> <type>bigint</type>,
<parameter>modification</parameter> <type>timestamp with time zone</type> )
</para>
<para>
Returns the name, size, and last modification time (mtime) of each
ordinary file in the server's write-ahead log (WAL) directory.
Filenames beginning with a dot, directories, and other special files
are excluded.
</para>
<para>
This function is restricted to superusers and members of
the <literal>pg_monitor</literal> role by default, but other users can
be granted EXECUTE to run the function.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_ls_archive_statusdir</primary>
</indexterm>
<function>pg_ls_archive_statusdir</function> ()
<returnvalue>setof record</returnvalue>
( <parameter>name</parameter> <type>text</type>,
<parameter>size</parameter> <type>bigint</type>,
<parameter>modification</parameter> <type>timestamp with time zone</type> )
</para>
<para>
Returns the name, size, and last modification time (mtime) of each
ordinary file in the server's WAL archive status directory
(<filename>pg_wal/archive_status</filename>). Filenames beginning
with a dot, directories, and other special files are excluded.
</para>
<para>
This function is restricted to superusers and members of
the <literal>pg_monitor</literal> role by default, but other users can
be granted EXECUTE to run the function.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_ls_tmpdir</primary>
</indexterm>
<function>pg_ls_tmpdir</function> ( <optional> <parameter>tablespace</parameter> <type>oid</type> </optional> )
<returnvalue>setof record</returnvalue>
( <parameter>name</parameter> <type>text</type>,
<parameter>size</parameter> <type>bigint</type>,
<parameter>modification</parameter> <type>timestamp with time zone</type> )
</para>
<para>
Returns the name, size, and last modification time (mtime) of each
ordinary file in the temporary file directory for the
specified <parameter>tablespace</parameter>.
If <parameter>tablespace</parameter> is not provided,
the <literal>pg_default</literal> tablespace is examined. Filenames
beginning with a dot, directories, and other special files are
excluded.
</para>
<para>
This function is restricted to superusers and members of
the <literal>pg_monitor</literal> role by default, but other users can
be granted EXECUTE to run the function.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_read_file</primary>
</indexterm>
<function>pg_read_file</function> ( <parameter>filename</parameter> <type>text</type> <optional>, <parameter>offset</parameter> <type>bigint</type>, <parameter>length</parameter> <type>bigint</type> <optional>, <parameter>missing_ok</parameter> <type>boolean</type> </optional></optional> )
<returnvalue>text</returnvalue>
</para>
<para>
Returns all or part of a text file, starting at the
given byte <parameter>offset</parameter>, returning at
most <parameter>length</parameter> bytes (less if the end of file is
reached first). If <parameter>offset</parameter> is negative, it is
relative to the end of the file. If <parameter>offset</parameter>
and <parameter>length</parameter> are omitted, the entire file is
returned. The bytes read from the file are interpreted as a string in
the database's encoding; an error is thrown if they are not valid in
that encoding.
</para>
<para>
This function is restricted to superusers by default, but other users
can be granted EXECUTE to run the function.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_read_binary_file</primary>
</indexterm>
<function>pg_read_binary_file</function> ( <parameter>filename</parameter> <type>text</type> <optional>, <parameter>offset</parameter> <type>bigint</type>, <parameter>length</parameter> <type>bigint</type> <optional>, <parameter>missing_ok</parameter> <type>boolean</type> </optional></optional> )
<returnvalue>bytea</returnvalue>
</para>
<para>
Returns all or part of a file. This function is identical to
<function>pg_read_file</function> except that it can read arbitrary
binary data, returning the result as <type>bytea</type>
not <type>text</type>; accordingly, no encoding checks are performed.
</para>
<para>
This function is restricted to superusers by default, but other users
can be granted EXECUTE to run the function.
</para>
<para>
In combination with the <function>convert_from</function> function,
this function can be used to read a text file in a specified encoding
and convert to the database's encoding:
<programlisting>
SELECT convert_from(pg_read_binary_file('file_in_utf8.txt'), 'UTF8');
</programlisting>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_stat_file</primary>
</indexterm>
<function>pg_stat_file</function> ( <parameter>filename</parameter> <type>text</type> <optional>, <parameter>missing_ok</parameter> <type>boolean</type> </optional> )
<returnvalue>record</returnvalue>
( <parameter>size</parameter> <type>bigint</type>,
<parameter>access</parameter> <type>timestamp with time zone</type>,
<parameter>modification</parameter> <type>timestamp with time zone</type>,
<parameter>change</parameter> <type>timestamp with time zone</type>,
<parameter>creation</parameter> <type>timestamp with time zone</type>,
<parameter>isdir</parameter> <type>boolean</type> )
</para>
<para>
Returns a record containing the file's size, last access time stamp,
last modification time stamp, last file status change time stamp (Unix
platforms only), file creation time stamp (Windows only), and a flag
indicating if it is a directory.
</para>
<para>
This function is restricted to superusers by default, but other users
can be granted EXECUTE to run the function.
</para></entry>
</row>
</tbody>
</tgroup>
</table>
</sect2>
<sect2 id="functions-advisory-locks">
<title>Advisory Lock Functions</title>
<para>
The functions shown in <xref linkend="functions-advisory-locks-table"/>
manage advisory locks. For details about proper use of these functions,
see <xref linkend="advisory-locks"/>.
</para>
<para>
All these functions are intended to be used to lock application-defined
resources, which can be identified either by a single 64-bit key value or
two 32-bit key values (note that these two key spaces do not overlap).
If another session already holds a conflicting lock on the same resource
identifier, the functions will either wait until the resource becomes
available, or return a <literal>false</literal> result, as appropriate for
the function.
Locks can be either shared or exclusive: a shared lock does not conflict
with other shared locks on the same resource, only with exclusive locks.
Locks can be taken at session level (so that they are held until released
or the session ends) or at transaction level (so that they are held until
the current transaction ends; there is no provision for manual release).
Multiple session-level lock requests stack, so that if the same resource
identifier is locked three times there must then be three unlock requests
to release the resource in advance of session end.
</para>
<table id="functions-advisory-locks-table">
<title>Advisory Lock Functions</title>
<tgroup cols="1">
<thead>
<row>
<entry role="func_table_entry"><para role="func_signature">
Function
</para>
<para>
Description
</para></entry>
</row>
</thead>
<tbody>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_advisory_lock</primary>
</indexterm>
<function>pg_advisory_lock</function> ( <parameter>key</parameter> <type>bigint</type> )
<returnvalue>void</returnvalue>
</para>
<para role="func_signature">
<function>pg_advisory_lock</function> ( <parameter>key1</parameter> <type>integer</type>, <parameter>key2</parameter> <type>integer</type> )
<returnvalue>void</returnvalue>
</para>
<para>
Obtains an exclusive session-level advisory lock, waiting if necessary.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_advisory_lock_shared</primary>
</indexterm>
<function>pg_advisory_lock_shared</function> ( <parameter>key</parameter> <type>bigint</type> )
<returnvalue>void</returnvalue>
</para>
<para role="func_signature">
<function>pg_advisory_lock_shared</function> ( <parameter>key1</parameter> <type>integer</type>, <parameter>key2</parameter> <type>integer</type> )
<returnvalue>void</returnvalue>
</para>
<para>
Obtains a shared session-level advisory lock, waiting if necessary.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_advisory_unlock</primary>
</indexterm>
<function>pg_advisory_unlock</function> ( <parameter>key</parameter> <type>bigint</type> )
<returnvalue>boolean</returnvalue>
</para>
<para role="func_signature">
<function>pg_advisory_unlock</function> ( <parameter>key1</parameter> <type>integer</type>, <parameter>key2</parameter> <type>integer</type> )
<returnvalue>boolean</returnvalue>
</para>
<para>
Releases a previously-acquired exclusive session-level advisory lock.
Returns <literal>true</literal> if the lock is successfully released.
If the lock was not held, <literal>false</literal> is returned, and in
addition, an SQL warning will be reported by the server.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_advisory_unlock_all</primary>
</indexterm>
<function>pg_advisory_unlock_all</function> ()
<returnvalue>void</returnvalue>
</para>
<para>
Releases all session-level advisory locks held by the current session.
(This function is implicitly invoked at session end, even if the
client disconnects ungracefully.)
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_advisory_unlock_shared</primary>
</indexterm>
<function>pg_advisory_unlock_shared</function> ( <parameter>key</parameter> <type>bigint</type> )
<returnvalue>boolean</returnvalue>
</para>
<para role="func_signature">
<function>pg_advisory_unlock_shared</function> ( <parameter>key1</parameter> <type>integer</type>, <parameter>key2</parameter> <type>integer</type> )
<returnvalue>boolean</returnvalue>
</para>
<para>
Releases a previously-acquired shared session-level advisory lock.
Returns <literal>true</literal> if the lock is successfully released.
If the lock was not held, <literal>false</literal> is returned, and in
addition, an SQL warning will be reported by the server.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_advisory_xact_lock</primary>
</indexterm>
<function>pg_advisory_xact_lock</function> ( <parameter>key</parameter> <type>bigint</type> )
<returnvalue>void</returnvalue>
</para>
<para role="func_signature">
<function>pg_advisory_xact_lock</function> ( <parameter>key1</parameter> <type>integer</type>, <parameter>key2</parameter> <type>integer</type> )
<returnvalue>void</returnvalue>
</para>
<para>
Obtains an exclusive transaction-level advisory lock, waiting if
necessary.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_advisory_xact_lock_shared</primary>
</indexterm>
<function>pg_advisory_xact_lock_shared</function> ( <parameter>key</parameter> <type>bigint</type> )
<returnvalue>void</returnvalue>
</para>
<para role="func_signature">
<function>pg_advisory_xact_lock_shared</function> ( <parameter>key1</parameter> <type>integer</type>, <parameter>key2</parameter> <type>integer</type> )
<returnvalue>void</returnvalue>
</para>
<para>
Obtains a shared transaction-level advisory lock, waiting if
necessary.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_try_advisory_lock</primary>
</indexterm>
<function>pg_try_advisory_lock</function> ( <parameter>key</parameter> <type>bigint</type> )
<returnvalue>boolean</returnvalue>
</para>
<para role="func_signature">
<function>pg_try_advisory_lock</function> ( <parameter>key1</parameter> <type>integer</type>, <parameter>key2</parameter> <type>integer</type> )
<returnvalue>boolean</returnvalue>
</para>
<para>
Obtains an exclusive session-level advisory lock if available.
This will either obtain the lock immediately and
return <literal>true</literal>, or return <literal>false</literal>
without waiting if the lock cannot be acquired immediately.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_try_advisory_lock_shared</primary>
</indexterm>
<function>pg_try_advisory_lock_shared</function> ( <parameter>key</parameter> <type>bigint</type> )
<returnvalue>boolean</returnvalue>
</para>
<para role="func_signature">
<function>pg_try_advisory_lock_shared</function> ( <parameter>key1</parameter> <type>integer</type>, <parameter>key2</parameter> <type>integer</type> )
<returnvalue>boolean</returnvalue>
</para>
<para>
Obtains a shared session-level advisory lock if available.
This will either obtain the lock immediately and
return <literal>true</literal>, or return <literal>false</literal>
without waiting if the lock cannot be acquired immediately.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_try_advisory_xact_lock</primary>
</indexterm>
<function>pg_try_advisory_xact_lock</function> ( <parameter>key</parameter> <type>bigint</type> )
<returnvalue>boolean</returnvalue>
</para>
<para role="func_signature">
<function>pg_try_advisory_xact_lock</function> ( <parameter>key1</parameter> <type>integer</type>, <parameter>key2</parameter> <type>integer</type> )
<returnvalue>boolean</returnvalue>
</para>
<para>
Obtains an exclusive transaction-level advisory lock if available.
This will either obtain the lock immediately and
return <literal>true</literal>, or return <literal>false</literal>
without waiting if the lock cannot be acquired immediately.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_try_advisory_xact_lock_shared</primary>
</indexterm>
<function>pg_try_advisory_xact_lock_shared</function> ( <parameter>key</parameter> <type>bigint</type> )
<returnvalue>boolean</returnvalue>
</para>
<para role="func_signature">
<function>pg_try_advisory_xact_lock_shared</function> ( <parameter>key1</parameter> <type>integer</type>, <parameter>key2</parameter> <type>integer</type> )
<returnvalue>boolean</returnvalue>
</para>
<para>
Obtains a shared transaction-level advisory lock if available.
This will either obtain the lock immediately and
return <literal>true</literal>, or return <literal>false</literal>
without waiting if the lock cannot be acquired immediately.
</para></entry>
</row>
</tbody>
</tgroup>
</table>
</sect2>
</sect1>
<sect1 id="functions-trigger">
<title>Trigger Functions</title>
<para>
While many uses of triggers involve user-written trigger functions,
<productname>PostgreSQL</productname> provides a few built-in trigger
functions that can be used directly in user-defined triggers. These
are summarized in <xref linkend="builtin-triggers-table"/>.
(Additional built-in trigger functions exist, which implement foreign
key constraints and deferred index constraints. Those are not documented
here since users need not use them directly.)
</para>
<para>
For more information about creating triggers, see
<xref linkend="sql-createtrigger"/>.
</para>
<table id="builtin-triggers-table">
<title>Built-In Trigger Functions</title>
<tgroup cols="1">
<thead>
<row>
<entry role="func_table_entry"><para role="func_signature">
Function
</para>
<para>
Description
</para>
<para>
Example Usage
</para></entry>
</row>
</thead>
<tbody>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>suppress_redundant_updates_trigger</primary>
</indexterm>
<function>suppress_redundant_updates_trigger</function> ( )
<returnvalue>trigger</returnvalue>
</para>
<para>
Suppresses do-nothing update operations. See below for details.
</para>
<para>
<literal>CREATE TRIGGER ... suppress_redundant_updates_trigger()</literal>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>tsvector_update_trigger</primary>
</indexterm>
<function>tsvector_update_trigger</function> ( )
<returnvalue>trigger</returnvalue>
</para>
<para>
Automatically updates a <type>tsvector</type> column from associated
plain-text document column(s). The text search configuration to use
is specified by name as a trigger argument. See
<xref linkend="textsearch-update-triggers"/> for details.
</para>
<para>
<literal>CREATE TRIGGER ... tsvector_update_trigger(tsvcol, 'pg_catalog.swedish', title, body)</literal>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>tsvector_update_trigger_column</primary>
</indexterm>
<function>tsvector_update_trigger_column</function> ( )
<returnvalue>trigger</returnvalue>
</para>
<para>
Automatically updates a <type>tsvector</type> column from associated
plain-text document column(s). The text search configuration to use
is taken from a <type>regconfig</type> column of the table. See
<xref linkend="textsearch-update-triggers"/> for details.
</para>
<para>
<literal>CREATE TRIGGER ... tsvector_update_trigger_column(tsvcol, tsconfigcol, title, body)</literal>
</para></entry>
</row>
</tbody>
</tgroup>
</table>
<para>
The <function>suppress_redundant_updates_trigger</function> function,
when applied as a row-level <literal>BEFORE UPDATE</literal> trigger,
will prevent any update that does not actually change the data in the
row from taking place. This overrides the normal behavior which always
performs a physical row update
regardless of whether or not the data has changed. (This normal behavior
makes updates run faster, since no checking is required, and is also
useful in certain cases.)
</para>
<para>
Ideally, you should avoid running updates that don't actually
change the data in the record. Redundant updates can cost considerable
unnecessary time, especially if there are lots of indexes to alter,
and space in dead rows that will eventually have to be vacuumed.
However, detecting such situations in client code is not
always easy, or even possible, and writing expressions to detect
them can be error-prone. An alternative is to use
<function>suppress_redundant_updates_trigger</function>, which will skip
updates that don't change the data. You should use this with care,
however. The trigger takes a small but non-trivial time for each record,
so if most of the records affected by updates do actually change,
use of this trigger will make updates run slower on average.
</para>
<para>
The <function>suppress_redundant_updates_trigger</function> function can be
added to a table like this:
<programlisting>
CREATE TRIGGER z_min_update
BEFORE UPDATE ON tablename
FOR EACH ROW EXECUTE FUNCTION suppress_redundant_updates_trigger();
</programlisting>
In most cases, you need to fire this trigger last for each row, so that
it does not override other triggers that might wish to alter the row.
Bearing in mind that triggers fire in name order, you would therefore
choose a trigger name that comes after the name of any other trigger
you might have on the table. (Hence the <quote>z</quote> prefix in the
example.)
</para>
</sect1>
<sect1 id="functions-event-triggers">
<title>Event Trigger Functions</title>
<para>
<productname>PostgreSQL</productname> provides these helper functions
to retrieve information from event triggers.
</para>
<para>
For more information about event triggers,
see <xref linkend="event-triggers"/>.
</para>
<sect2 id="pg-event-trigger-ddl-command-end-functions">
<title>Capturing Changes at Command End</title>
<indexterm>
<primary>pg_event_trigger_ddl_commands</primary>
</indexterm>
<synopsis>
<function>pg_event_trigger_ddl_commands</function> () <returnvalue>setof record</returnvalue>
</synopsis>
<para>
<function>pg_event_trigger_ddl_commands</function> returns a list of
<acronym>DDL</acronym> commands executed by each user action,
when invoked in a function attached to a
<literal>ddl_command_end</literal> event trigger. If called in any other
context, an error is raised.
<function>pg_event_trigger_ddl_commands</function> returns one row for each
base command executed; some commands that are a single SQL sentence
may return more than one row. This function returns the following
columns:
<informaltable>
<tgroup cols="3">
<thead>
<row>
<entry>Name</entry>
<entry>Type</entry>
<entry>Description</entry>
</row>
</thead>
<tbody>
<row>
<entry><literal>classid</literal></entry>
<entry><type>oid</type></entry>
<entry>OID of catalog the object belongs in</entry>
</row>
<row>
<entry><literal>objid</literal></entry>
<entry><type>oid</type></entry>
<entry>OID of the object itself</entry>
</row>
<row>
<entry><literal>objsubid</literal></entry>
<entry><type>integer</type></entry>
<entry>Sub-object ID (e.g., attribute number for a column)</entry>
</row>
<row>
<entry><literal>command_tag</literal></entry>
<entry><type>text</type></entry>
<entry>Command tag</entry>
</row>
<row>
<entry><literal>object_type</literal></entry>
<entry><type>text</type></entry>
<entry>Type of the object</entry>
</row>
<row>
<entry><literal>schema_name</literal></entry>
<entry><type>text</type></entry>
<entry>
Name of the schema the object belongs in, if any; otherwise <literal>NULL</literal>.
No quoting is applied.
</entry>
</row>
<row>
<entry><literal>object_identity</literal></entry>
<entry><type>text</type></entry>
<entry>
Text rendering of the object identity, schema-qualified. Each
identifier included in the identity is quoted if necessary.
</entry>
</row>
<row>
<entry><literal>in_extension</literal></entry>
<entry><type>boolean</type></entry>
<entry>True if the command is part of an extension script</entry>
</row>
<row>
<entry><literal>command</literal></entry>
<entry><type>pg_ddl_command</type></entry>
<entry>
A complete representation of the command, in internal format.
This cannot be output directly, but it can be passed to other
functions to obtain different pieces of information about the
command.
</entry>
</row>
</tbody>
</tgroup>
</informaltable>
</para>
</sect2>
<sect2 id="pg-event-trigger-sql-drop-functions">
<title>Processing Objects Dropped by a DDL Command</title>
<indexterm>
<primary>pg_event_trigger_dropped_objects</primary>
</indexterm>
<synopsis>
<function>pg_event_trigger_dropped_objects</function> () <returnvalue>setof record</returnvalue>
</synopsis>
<para>
<function>pg_event_trigger_dropped_objects</function> returns a list of all objects
dropped by the command in whose <literal>sql_drop</literal> event it is called.
If called in any other context, an error is raised.
This function returns the following columns:
<informaltable>
<tgroup cols="3">
<thead>
<row>
<entry>Name</entry>
<entry>Type</entry>
<entry>Description</entry>
</row>
</thead>
<tbody>
<row>
<entry><literal>classid</literal></entry>
<entry><type>oid</type></entry>
<entry>OID of catalog the object belonged in</entry>
</row>
<row>
<entry><literal>objid</literal></entry>
<entry><type>oid</type></entry>
<entry>OID of the object itself</entry>
</row>
<row>
<entry><literal>objsubid</literal></entry>
<entry><type>integer</type></entry>
<entry>Sub-object ID (e.g., attribute number for a column)</entry>
</row>
<row>
<entry><literal>original</literal></entry>
<entry><type>boolean</type></entry>
<entry>True if this was one of the root object(s) of the deletion</entry>
</row>
<row>
<entry><literal>normal</literal></entry>
<entry><type>boolean</type></entry>
<entry>
True if there was a normal dependency relationship
in the dependency graph leading to this object
</entry>
</row>
<row>
<entry><literal>is_temporary</literal></entry>
<entry><type>boolean</type></entry>
<entry>
True if this was a temporary object
</entry>
</row>
<row>
<entry><literal>object_type</literal></entry>
<entry><type>text</type></entry>
<entry>Type of the object</entry>
</row>
<row>
<entry><literal>schema_name</literal></entry>
<entry><type>text</type></entry>
<entry>
Name of the schema the object belonged in, if any; otherwise <literal>NULL</literal>.
No quoting is applied.
</entry>
</row>
<row>
<entry><literal>object_name</literal></entry>
<entry><type>text</type></entry>
<entry>
Name of the object, if the combination of schema and name can be
used as a unique identifier for the object; otherwise <literal>NULL</literal>.
No quoting is applied, and name is never schema-qualified.
</entry>
</row>
<row>
<entry><literal>object_identity</literal></entry>
<entry><type>text</type></entry>
<entry>
Text rendering of the object identity, schema-qualified. Each
identifier included in the identity is quoted if necessary.
</entry>
</row>
<row>
<entry><literal>address_names</literal></entry>
<entry><type>text[]</type></entry>
<entry>
An array that, together with <literal>object_type</literal> and
<literal>address_args</literal>, can be used by
the <function>pg_get_object_address</function> function to
recreate the object address in a remote server containing an
identically named object of the same kind.
</entry>
</row>
<row>
<entry><literal>address_args</literal></entry>
<entry><type>text[]</type></entry>
<entry>
Complement for <literal>address_names</literal>
</entry>
</row>
</tbody>
</tgroup>
</informaltable>
</para>
<para>
The <function>pg_event_trigger_dropped_objects</function> function can be used
in an event trigger like this:
<programlisting>
CREATE FUNCTION test_event_trigger_for_drops()
RETURNS event_trigger LANGUAGE plpgsql AS $$
DECLARE
obj record;
BEGIN
FOR obj IN SELECT * FROM pg_event_trigger_dropped_objects()
LOOP
RAISE NOTICE '% dropped object: % %.% %',
tg_tag,
obj.object_type,
obj.schema_name,
obj.object_name,
obj.object_identity;
END LOOP;
END;
$$;
CREATE EVENT TRIGGER test_event_trigger_for_drops
ON sql_drop
EXECUTE FUNCTION test_event_trigger_for_drops();
</programlisting>
</para>
</sect2>
<sect2 id="pg-event-trigger-table-rewrite-functions">
<title>Handling a Table Rewrite Event</title>
<para>
The functions shown in
<xref linkend="functions-event-trigger-table-rewrite"/>
provide information about a table for which a
<literal>table_rewrite</literal> event has just been called.
If called in any other context, an error is raised.
</para>
<table id="functions-event-trigger-table-rewrite">
<title>Table Rewrite Information Functions</title>
<tgroup cols="1">
<thead>
<row>
<entry role="func_table_entry"><para role="func_signature">
Function
</para>
<para>
Description
</para></entry>
</row>
</thead>
<tbody>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_event_trigger_table_rewrite_oid</primary>
</indexterm>
<function>pg_event_trigger_table_rewrite_oid</function> ()
<returnvalue>oid</returnvalue>
</para>
<para>
Returns the OID of the table about to be rewritten.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_event_trigger_table_rewrite_reason</primary>
</indexterm>
<function>pg_event_trigger_table_rewrite_reason</function> ()
<returnvalue>integer</returnvalue>
</para>
<para>
Returns a code explaining the reason(s) for rewriting. The exact
meaning of the codes is release dependent.
</para></entry>
</row>
</tbody>
</tgroup>
</table>
<para>
These functions can be used in an event trigger like this:
<programlisting>
CREATE FUNCTION test_event_trigger_table_rewrite_oid()
RETURNS event_trigger
LANGUAGE plpgsql AS
$$
BEGIN
RAISE NOTICE 'rewriting table % for reason %',
pg_event_trigger_table_rewrite_oid()::regclass,
pg_event_trigger_table_rewrite_reason();
END;
$$;
CREATE EVENT TRIGGER test_table_rewrite_oid
ON table_rewrite
EXECUTE FUNCTION test_event_trigger_table_rewrite_oid();
</programlisting>
</para>
</sect2>
</sect1>
<sect1 id="functions-statistics">
<title>Statistics Information Functions</title>
<indexterm zone="functions-statistics">
<primary>function</primary>
<secondary>statistics</secondary>
</indexterm>
<para>
<productname>PostgreSQL</productname> provides a function to inspect complex
statistics defined using the <command>CREATE STATISTICS</command> command.
</para>
<sect2 id="functions-statistics-mcv">
<title>Inspecting MCV Lists</title>
<indexterm>
<primary>pg_mcv_list_items</primary>
</indexterm>
<synopsis>
<function>pg_mcv_list_items</function> ( <type>pg_mcv_list</type> ) <returnvalue>setof record</returnvalue>
</synopsis>
<para>
<function>pg_mcv_list_items</function> returns a set of records describing
all items stored in a multi-column <acronym>MCV</acronym> list. It
returns the following columns:
<informaltable>
<tgroup cols="3">
<thead>
<row>
<entry>Name</entry>
<entry>Type</entry>
<entry>Description</entry>
</row>
</thead>
<tbody>
<row>
<entry><literal>index</literal></entry>
<entry><type>integer</type></entry>
<entry>index of the item in the <acronym>MCV</acronym> list</entry>
</row>
<row>
<entry><literal>values</literal></entry>
<entry><type>text[]</type></entry>
<entry>values stored in the MCV item</entry>
</row>
<row>
<entry><literal>nulls</literal></entry>
<entry><type>boolean[]</type></entry>
<entry>flags identifying <literal>NULL</literal> values</entry>
</row>
<row>
<entry><literal>frequency</literal></entry>
<entry><type>double precision</type></entry>
<entry>frequency of this <acronym>MCV</acronym> item</entry>
</row>
<row>
<entry><literal>base_frequency</literal></entry>
<entry><type>double precision</type></entry>
<entry>base frequency of this <acronym>MCV</acronym> item</entry>
</row>
</tbody>
</tgroup>
</informaltable>
</para>
<para>
The <function>pg_mcv_list_items</function> function can be used like this:
<programlisting>
SELECT m.* FROM pg_statistic_ext join pg_statistic_ext_data on (oid = stxoid),
pg_mcv_list_items(stxdmcv) m WHERE stxname = 'stts';
</programlisting>
Values of the <type>pg_mcv_list</type> type can be obtained only from the
<structname>pg_statistic_ext_data</structname>.<structfield>stxdmcv</structfield>
column.
</para>
</sect2>
</sect1>
</chapter>