Skip to content

P
Postgres FD Implementation
Commit 48ba3f57 authored by Peter Eisentraut's avatar Peter Eisentraut
Browse files
Options

Update documentation on XML functions

parent b39e9150
Hide whitespace changes
Inline Side-by-side
Showing with 367 additions and 127 deletions
doc/src/sgml/datatype.sgml
View file @ 48ba3f57
<!-- $PostgreSQL: pgsql/doc/src/sgml/datatype.sgml,v 1.186 2007/01/25 11:53:50 petere Exp $ --> <!-- $PostgreSQL: pgsql/doc/src/sgml/datatype.sgml,v 1.187 2007/01/29 13:24:30 petere Exp $ -->
<chapter id="datatype"> <chapter id="datatype">
<title id="datatype-title">Data Types</title> <title id="datatype-title">Data Types</title>
...@@ -3538,86 +3538,6 @@ SET xmloption TO { DOCUMENT | CONTENT }; ...@@ -3538,86 +3538,6 @@ SET xmloption TO { DOCUMENT | CONTENT };
processed in UTF-8, computations will be most efficient if the processed in UTF-8, computations will be most efficient if the
server encoding is also UTF-8. server encoding is also UTF-8.
</para> </para>
<para>
<acronym>XML</> (Extensible Markup Language) support is not
just the existance of an <type>xml</type> data type, but a
variety of features supported by a database system. These
capabilities include import/export, indexing, searching,
transforming, and <acronym>XML</> to <acronym>SQL</> mapping.
<productname>PostgreSQL</> supports some but not all of these
<acronym>XML</> capabilities. For an overview of <acronym>XML</>
use in databases, see <ulink
url="http://www.rpbourret.com/xml/XMLAndDatabases.htm"></>.
</para>
<variablelist>
<varlistentry>
<term>Import/Export</term>
<listitem>
<para>
There is no facility for mapping <acronym>XML</> to relational
tables. An external tool must be used for this. One simple way to
export <acronym>XML</> is to use <application>psql</> in
<acronym>HTML</> mode (<literal>\pset format html</>), and convert
the <acronym>XHTML</> output to XML using an external tool.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>Indexing</term>
<listitem>
<para>
<filename>/contrib/xml2</> functions can be used in expression
indexes to index specific <acronym>XML</> fields. To index the
full contents of <acronym>XML</> documents, the full-text indexing
tool <filename>/contrib/tsearch2</> can be used. Of course,
Tsearch2 indexes have no <acronym>XML</> awareness so additional
<filename>/contrib/xml2</> checks should be added to queries.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>Searching</term>
<listitem>
<para>
XPath searches are implemented using <filename>/contrib/xml2</>.
It processes <acronym>XML</> text documents and returns results
based on the requested query.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>Transforming</term>
<listitem>
<para>
<filename>/contrib/xml2</> supports <acronym>XSLT</> (Extensible
Stylesheet Language Transformation).
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>XML to SQL Mapping</term>
<listitem>
<para>
This involves converting <acronym>XML</> data to and from
relational structures. <productname>PostgreSQL</> has no internal
support for such mapping, and relies on external tools to do such
conversions.
</para>
</listitem>
</varlistentry>
</variablelist>
</sect1> </sect1>
</chapter> </chapter>
doc/src/sgml/func.sgml
View file @ 48ba3f57
<!-- $PostgreSQL: pgsql/doc/src/sgml/func.sgml,v 1.352 2007/01/20 21:59:34 neilc Exp $ --> <!-- $PostgreSQL: pgsql/doc/src/sgml/func.sgml,v 1.353 2007/01/29 13:24:30 petere Exp $ -->
<chapter id="functions"> <chapter id="functions">
<title>Functions and Operators</title> <title>Functions and Operators</title>
...@@ -10752,65 +10752,215 @@ SELECT (pg_stat_file('filename')).modification; ...@@ -10752,65 +10752,215 @@ SELECT (pg_stat_file('filename')).modification;
</sect1> </sect1>
<sect1 id="functions-xml"> <sect1 id="functions-xml">
<title>XML Functions</title> <title>XML Functions</title>
<para>
The functions and function-like expressions described in this
section operate on values of type <type>xml</type>. Check <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 not repeated here.
</para>
<sect2>
<title>Producing XML Content</title>
<para> <para>
The functions and function-like expressions described in this A set of functions and function-like expressions are available for
section operate on values of type <type>xml</type>. 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> </para>
<sect2> <sect3>
<title><literal>xmlcomment</literal></title> <title><literal>xmlcomment</literal></title>
<indexterm> <indexterm>
<primary>xmlcomment</primary> <primary>xmlcomment</primary>
</indexterm> </indexterm>
<synopsis> <synopsis>
<function>xmlcomment</function>(<replaceable>text</replaceable>) <function>xmlcomment</function>(<replaceable>text</replaceable>)
</synopsis> </synopsis>
<para> <para>
Creates an XML comment. The function <function>xmlcomment</function> creates an XML value
containing an XML comment with the specified text as content.
The text may not contain <literal>--</literal> or end with a
<literal>-</literal> so that the resulting construct is a valid
XML comment. If the argument is null, the result is null.
</para> </para>
</sect2>
<para>
<sect2> Example:
<screen><![CDATA[
SELECT xmlcomment('hello');
xmlcomment
--------------
<!--hello-->
]]></screen>
</para>
</sect3>
<sect3>
<title><literal>xmlconcat</literal></title> <title><literal>xmlconcat</literal></title>
<indexterm> <indexterm>
<primary>xmlconcat</primary> <primary>xmlconcat</primary>
</indexterm> </indexterm>
<synopsis> <synopsis>
<function>xmlconcat</function>(<replaceable>xml</replaceable><optional>, xml, ...</optional>) <function>xmlconcat</function>(<replaceable>xml</replaceable><optional>, ...</optional>)
</synopsis> </synopsis>
<para> <para>
Combines a list of individual XML values to create a The function <function>xmlconcat</function> concatenates a list
single value containing an XML forest. 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>
</sect2>
<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>
<sect2> <sect3>
<title><literal>xmlelement</literal></title> <title><literal>xmlelement</literal></title>
<indexterm> <indexterm>
<primary>xmlelement</primary> <primary>xmlelement</primary>
</indexterm> </indexterm>
<synopsis> <synopsis>
<function>xmlelement</function>(name <replaceable>name</replaceable><optional>, xmlattribytes(<replaceable>value</replaceable> <optional>AS <replaceable>label</replaceable></optional><optional>, ... </optional>)</optional> <function>xmlelement</function>(name <replaceable>name</replaceable> <optional>, xmlattributes(<replaceable>value</replaceable> <optional>AS <replaceable>attname</replaceable></optional> <optional>, ... </optional>)</optional> <optional><replaceable>, content, ...</replaceable></optional>)
<optional><replaceable>, content, ...</replaceable></optional>)
</synopsis> </synopsis>
<para> <para>
Creates an XML element, allowing the name to be specified. The <function>xmlelement</function> expression produces an XML
element with the given name, attributes, and 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>
</sect2>
<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 attribute name by default. In any other case, 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
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 &lt;, &gt;,
and &amp; 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 evolve in order to align the
SQL and PostgreSQL data types with the XML Schema specification,
at which point a more precise description will appear.
</para>
</sect3>
<sect2> <sect3>
<title><literal>xmlforest</literal></title> <title><literal>xmlforest</literal></title>
<indexterm> <indexterm>
...@@ -10818,16 +10968,54 @@ SELECT (pg_stat_file('filename')).modification; ...@@ -10818,16 +10968,54 @@ SELECT (pg_stat_file('filename')).modification;
</indexterm> </indexterm>
<synopsis> <synopsis>
<function>xmlforest</function>(<replaceable>value</replaceable> <optional>AS <replaceable>label</replaceable></optional><optional>, ...</optional>) <function>xmlforest</function>(<replaceable>content</replaceable> <optional>AS <replaceable>name</replaceable></optional> <optional>, ...</optional>)
</synopsis> </synopsis>
<para> <para>
Creates XML elements from columns, using the name of each The <function>xmlforest</function> expression produces an XML
column as the name of the corresponding element. forest (sequence) of elements using the given names and content.
</para>
<para>
Examples:
<screen><![CDATA[
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
-------------------------------------------------------------------------------------------
<table_name>pg_authid</table_name><column_name>rolname</column_name>
<table_name>pg_authid</table_name><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> </para>
</sect2> </sect3>
<sect2> <sect3>
<title><literal>xmlpi</literal></title> <title><literal>xmlpi</literal></title>
<indexterm> <indexterm>
...@@ -10839,11 +11027,24 @@ SELECT (pg_stat_file('filename')).modification; ...@@ -10839,11 +11027,24 @@ SELECT (pg_stat_file('filename')).modification;
</synopsis> </synopsis>
<para> <para>
Creates an XML processing instruction. The <function>xmlpi</function> expression creates an XML
processing instruction. The content, if present, must not
contain the character sequence <literal>?&lt;</literal>.
</para>
<para>
Example:
<screen><![CDATA[
SELECT xmlpi(name php, 'echo "hello world";');
xmlpi
-----------------------------
<?php echo "hello world";?>
]]></screen>
</para> </para>
</sect2> </sect3>
<sect2> <sect3>
<title><literal>xmlroot</literal></title> <title><literal>xmlroot</literal></title>
<indexterm> <indexterm>
...@@ -10851,13 +11052,132 @@ SELECT (pg_stat_file('filename')).modification; ...@@ -10851,13 +11052,132 @@ SELECT (pg_stat_file('filename')).modification;
</indexterm> </indexterm>
<synopsis> <synopsis>
<function>xmlroot</function>(<replaceable>xml</replaceable>, version <replaceable>text</replaceable> <optional>, standalone yes|no|no value</optional>) <function>xmlroot</function>(<replaceable>xml</replaceable>, version <replaceable>text</replaceable>|no value <optional>, standalone yes|no|no value</optional>)
</synopsis> </synopsis>
<para> <para>
Creates the root node of an XML document. The <function>xmlroot</function> expression alters the properties
of the root node of an XML value. If a version is specified,
this replaces the value in the version declaration, if a
standalone value is specified, this replaces the value in the
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>
<title>XML Predicates</title>
<indexterm>
<primary>IS DOCUMENT</primary>
</indexterm>
<synopsis>
<replaceable>xml</replaceable> IS DOCUMENT
</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> </para>
</sect3>
</sect2>
<sect2>
<title>Processing XML</title>
<para>
<acronym>XML</> support is not just the existence of an
<type>xml</type> data type, but a variety of features supported by
a database system. These capabilities include import/export,
indexing, searching, transforming, and <acronym>XML</> to
<acronym>SQL</> mapping. <productname>PostgreSQL</> supports some
but not all of these <acronym>XML</> capabilities. For an
overview of <acronym>XML</> use in databases, see <ulink
url="http://www.rpbourret.com/xml/XMLAndDatabases.htm"></>.
</para>
<variablelist>
<varlistentry>
<term>Import/Export</term>
<listitem>
<para>
There is no facility for mapping <acronym>XML</> to relational
tables. An external tool must be used for this. One simple way
to export <acronym>XML</> is to use <application>psql</> in
<acronym>HTML</> mode (<literal>\pset format html</>), and
convert the <acronym>XHTML</> output to XML using an external
tool.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>Indexing</term>
<listitem>
<para>
<filename>contrib/xml2/</> functions can be used in expression
indexes to index specific <acronym>XML</> fields. To index the
full contents of <acronym>XML</> documents, the full-text
indexing tool <filename>contrib/tsearch2/</> can be used. Of
course, Tsearch2 indexes have no <acronym>XML</> awareness so
additional <filename>contrib/xml2/</> checks should be added to
queries.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>Searching</term>
<listitem>
<para>
XPath searches are implemented using <filename>contrib/xml2/</>.
It processes <acronym>XML</> text documents and returns results
based on the requested query.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>Transforming</term>
<listitem>
<para>
<filename>contrib/xml2/</> supports <acronym>XSLT</> (Extensible
Stylesheet Language Transformation).
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>XML to SQL Mapping</term>
<listitem>
<para>
This involves converting <acronym>XML</> data to and from
relational structures. <productname>PostgreSQL</> has no
internal support for such mapping, and relies on external tools
to do such conversions.
</para>
</listitem>
</varlistentry>
</variablelist>
</sect2> </sect2>
</sect1> </sect1>
</chapter> </chapter>
Markdown is supported
0% or
You are about to add 0 people to the discussion. Proceed with caution.
Finish editing this message first!
Please register or to comment