<!--
doc/src/sgml/ref/create_table.sgml
PostgreSQL documentation
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<refentry id="SQL-CREATETABLE">
 <refmeta>
  <refentrytitle>CREATE TABLE</refentrytitle>
  <manvolnum>7</manvolnum>
  <refmiscinfo>SQL - Language Statements</refmiscinfo>
 </refmeta>

 <refnamediv>
  <refname>CREATE TABLE</refname>
  <refpurpose>define a new table</refpurpose>
 </refnamediv>

 <indexterm zone="sql-createtable">
  <primary>CREATE TABLE</primary>
 </indexterm>

 <refsynopsisdiv>
<synopsis>
CREATE [ [ GLOBAL | LOCAL ] { TEMPORARY | TEMP } | UNLOGGED ] TABLE [ IF NOT EXISTS ] <replaceable class="PARAMETER">table_name</replaceable> ( [
  { <replaceable class="PARAMETER">column_name</replaceable> <replaceable class="PARAMETER">data_type</replaceable> [ COLLATE <replaceable>collation</replaceable> ] [ <replaceable class="PARAMETER">column_constraint</replaceable> [ ... ] ]
    | <replaceable>table_constraint</replaceable>
    | LIKE <replaceable>source_table</replaceable> [ <replaceable>like_option</replaceable> ... ] }
    [, ... ]
] )
[ INHERITS ( <replaceable>parent_table</replaceable> [, ... ] ) ]
[ WITH ( <replaceable class="PARAMETER">storage_parameter</replaceable> [= <replaceable class="PARAMETER">value</replaceable>] [, ... ] ) | WITH OIDS | WITHOUT OIDS ]
[ ON COMMIT { PRESERVE ROWS | DELETE ROWS | DROP } ]
[ TABLESPACE <replaceable class="PARAMETER">tablespace_name</replaceable> ]

CREATE [ [ GLOBAL | LOCAL ] { TEMPORARY | TEMP } | UNLOGGED ] TABLE [ IF NOT EXISTS ] <replaceable class="PARAMETER">table_name</replaceable>
    OF <replaceable class="PARAMETER">type_name</replaceable> [ (
  { <replaceable class="PARAMETER">column_name</replaceable> WITH OPTIONS [ <replaceable class="PARAMETER">column_constraint</replaceable> [ ... ] ]
    | <replaceable>table_constraint</replaceable> }
    [, ... ]
) ]
[ WITH ( <replaceable class="PARAMETER">storage_parameter</replaceable> [= <replaceable class="PARAMETER">value</replaceable>] [, ... ] ) | WITH OIDS | WITHOUT OIDS ]
[ ON COMMIT { PRESERVE ROWS | DELETE ROWS | DROP } ]
[ TABLESPACE <replaceable class="PARAMETER">tablespace_name</replaceable> ]

<phrase>where <replaceable class="PARAMETER">column_constraint</replaceable> is:</phrase>

[ CONSTRAINT <replaceable class="PARAMETER">constraint_name</replaceable> ]
{ NOT NULL |
  NULL |
  CHECK ( <replaceable class="PARAMETER">expression</replaceable> ) [ NO INHERIT ] |
  DEFAULT <replaceable>default_expr</replaceable> |
  UNIQUE <replaceable class="PARAMETER">index_parameters</replaceable> |
  PRIMARY KEY <replaceable class="PARAMETER">index_parameters</replaceable> |
  REFERENCES <replaceable class="PARAMETER">reftable</replaceable> [ ( <replaceable class="PARAMETER">refcolumn</replaceable> ) ] [ MATCH FULL | MATCH PARTIAL | MATCH SIMPLE ]
    [ ON DELETE <replaceable class="parameter">action</replaceable> ] [ ON UPDATE <replaceable class="parameter">action</replaceable> ] }
[ DEFERRABLE | NOT DEFERRABLE ] [ INITIALLY DEFERRED | INITIALLY IMMEDIATE ]

<phrase>and <replaceable class="PARAMETER">table_constraint</replaceable> is:</phrase>

[ CONSTRAINT <replaceable class="PARAMETER">constraint_name</replaceable> ]
{ CHECK ( <replaceable class="PARAMETER">expression</replaceable> ) [ NO INHERIT ] |
  UNIQUE ( <replaceable class="PARAMETER">column_name</replaceable> [, ... ] ) <replaceable class="PARAMETER">index_parameters</replaceable> |
  PRIMARY KEY ( <replaceable class="PARAMETER">column_name</replaceable> [, ... ] ) <replaceable class="PARAMETER">index_parameters</replaceable> |
  EXCLUDE [ USING <replaceable class="parameter">index_method</replaceable> ] ( <replaceable class="parameter">exclude_element</replaceable> WITH <replaceable class="parameter">operator</replaceable> [, ... ] ) <replaceable class="parameter">index_parameters</replaceable> [ WHERE ( <replaceable class="parameter">predicate</replaceable> ) ] |
  FOREIGN KEY ( <replaceable class="PARAMETER">column_name</replaceable> [, ... ] ) REFERENCES <replaceable class="PARAMETER">reftable</replaceable> [ ( <replaceable class="PARAMETER">refcolumn</replaceable> [, ... ] ) ]
    [ MATCH FULL | MATCH PARTIAL | MATCH SIMPLE ] [ ON DELETE <replaceable class="parameter">action</replaceable> ] [ ON UPDATE <replaceable class="parameter">action</replaceable> ] }
[ DEFERRABLE | NOT DEFERRABLE ] [ INITIALLY DEFERRED | INITIALLY IMMEDIATE ]

<phrase>and <replaceable class="PARAMETER">like_option</replaceable> is:</phrase>

{ INCLUDING | EXCLUDING } { DEFAULTS | CONSTRAINTS | INDEXES | STORAGE | COMMENTS | ALL }

<phrase><replaceable class="PARAMETER">index_parameters</replaceable> in <literal>UNIQUE</literal>, <literal>PRIMARY KEY</literal>, and <literal>EXCLUDE</literal> constraints are:</phrase>

[ WITH ( <replaceable class="PARAMETER">storage_parameter</replaceable> [= <replaceable class="PARAMETER">value</replaceable>] [, ... ] ) ]
[ USING INDEX TABLESPACE <replaceable class="PARAMETER">tablespace_name</replaceable> ]

<phrase><replaceable class="PARAMETER">exclude_element</replaceable> in an <literal>EXCLUDE</literal> constraint is:</phrase>

{ <replaceable class="parameter">column_name</replaceable> | ( <replaceable class="parameter">expression</replaceable> ) } [ <replaceable class="parameter">opclass</replaceable> ] [ ASC | DESC ] [ NULLS { FIRST | LAST } ]
</synopsis>

 </refsynopsisdiv>

 <refsect1 id="SQL-CREATETABLE-description">
  <title>Description</title>

  <para>
   <command>CREATE TABLE</command> will create a new, initially empty table
   in the current database. The table will be owned by the user issuing the
   command.
  </para>

  <para>
   If a schema name is given (for example, <literal>CREATE TABLE
   myschema.mytable ...</>) then the table is created in the specified
   schema.  Otherwise it is created in the current schema.  Temporary
   tables exist in a special schema, so a schema name cannot be given
   when creating a temporary table.  The name of the table must be
   distinct from the name of any other table, sequence, index, view,
   or foreign table in the same schema.
  </para>

  <para>
   <command>CREATE TABLE</command> also automatically creates a data
   type that represents the composite type corresponding
   to one row of the table.  Therefore, tables cannot have the same
   name as any existing data type in the same schema.
  </para>

  <para>
   The optional constraint clauses specify constraints (tests) that
   new or updated rows must satisfy for an insert or update operation
   to succeed.  A constraint is an SQL object that helps define the
   set of valid values in the table in various ways.
  </para>

  <para>
   There are two ways to define constraints: table constraints and
   column constraints.  A column constraint is defined as part of a
   column definition.  A table constraint definition is not tied to a
   particular column, and it can encompass more than one column.
   Every column constraint can also be written as a table constraint;
   a column constraint is only a notational convenience for use when the
   constraint only affects one column.
  </para>

  <para>
   To be able to create a table, you must have <literal>USAGE</literal>
   privilege on all column types or the type in the <literal>OF</literal>
   clause, respectively.
  </para>
 </refsect1>

 <refsect1>
  <title>Parameters</title>

  <variablelist>

   <varlistentry>
    <term><literal>TEMPORARY</> or <literal>TEMP</></term>
    <listitem>
     <para>
      If specified, the table is created as a temporary table.
      Temporary tables are automatically dropped at the end of a
      session, or optionally at the end of the current transaction
      (see <literal>ON COMMIT</literal> below).  Existing permanent
      tables with the same name are not visible to the current session
      while the temporary table exists, unless they are referenced
      with schema-qualified names. Any indexes created on a temporary
      table are automatically temporary as well.
     </para>

     <para>
      The <link linkend="autovacuum">autovacuum daemon</link> cannot
      access and therefore cannot vacuum or analyze temporary tables.
      For this reason, appropriate vacuum and analyze operations should be
      performed via session SQL commands.  For example, if a temporary
      table is going to be used in complex queries, it is wise to run
      <command>ANALYZE</> on the temporary table after it is populated.
     </para>

     <para>
      Optionally, <literal>GLOBAL</literal> or <literal>LOCAL</literal>
      can be written before <literal>TEMPORARY</> or <literal>TEMP</>.
      This presently makes no difference in <productname>PostgreSQL</>
      and is deprecated; see
      <xref linkend="sql-createtable-compatibility"
      endterm="sql-createtable-compatibility-title">.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><literal>UNLOGGED</></term>
    <listitem>
     <para>
      If specified, the table is created as an unlogged table.  Data written
      to unlogged tables is not written to the write-ahead log (see <xref
      linkend="wal">), which makes them considerably faster than ordinary
      tables.  However, they are not crash-safe: an unlogged table is
      automatically truncated after a crash or unclean shutdown.  The contents
      of an unlogged table are also not replicated to standby servers.
      Any indexes created on an unlogged table are automatically unlogged as
      well; however, unlogged <link linkend="GiST">GiST indexes</link> are
      currently not supported and cannot be created on an unlogged table.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><literal>IF NOT EXISTS</></term>
    <listitem>
     <para>
      Do not throw an error if a relation with the same name already exists.
      A notice is issued in this case.  Note that there is no guarantee that
      the existing relation is anything like the one that would have been
      created.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><replaceable class="PARAMETER">table_name</replaceable></term>
    <listitem>
     <para>
      The name (optionally schema-qualified) of the table to be created.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><literal>OF <replaceable class="PARAMETER">type_name</replaceable></literal></term>
    <listitem>
     <para>
      Creates a <firstterm>typed table</firstterm>, which takes its
      structure from the specified composite type (name optionally
      schema-qualified).  A typed table is tied to its type; for
      example the table will be dropped if the type is dropped
      (with <literal>DROP TYPE ... CASCADE</literal>).
     </para>

     <para>
      When a typed table is created, then the data types of the
      columns are determined by the underlying composite type and are
      not specified by the <literal>CREATE TABLE</literal> command.
      But the <literal>CREATE TABLE</literal> command can add defaults
      and constraints to the table and can specify storage parameters.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><replaceable class="PARAMETER">column_name</replaceable></term>
    <listitem>
     <para>
      The name of a column to be created in the new table.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><replaceable class="PARAMETER">data_type</replaceable></term>
    <listitem>
     <para>
      The data type of the column. This can include array
      specifiers. For more information on the data types supported by
      <productname>PostgreSQL</productname>, refer to <xref
      linkend="datatype">.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><literal>COLLATE <replaceable>collation</replaceable></literal></term>
    <listitem>
     <para>
      The <literal>COLLATE</> clause assigns a collation to
      the column (which must be of a collatable data type).
      If not specified, the column data type's default collation is used.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><literal>INHERITS ( <replaceable>parent_table</replaceable> [, ... ] )</literal></term>
    <listitem>
     <para>
      The optional <literal>INHERITS</> clause specifies a list of
      tables from which the new table automatically inherits all
      columns.
     </para>

     <para>
      Use of <literal>INHERITS</> creates a persistent relationship
      between the new child table and its parent table(s).  Schema
      modifications to the parent(s) normally propagate to children
      as well, and by default the data of the child table is included in
      scans of the parent(s).
     </para>

     <para>
      If the same column name exists in more than one parent
      table, an error is reported unless the data types of the columns
      match in each of the parent tables.  If there is no conflict,
      then the duplicate columns are merged to form a single column in
      the new table.  If the column name list of the new table
      contains a column name that is also inherited, the data type must
      likewise match the inherited column(s), and the column
      definitions are merged into one.  If the
      new table explicitly specifies a default value for the column,
      this default overrides any defaults from inherited declarations
      of the column.  Otherwise, any parents that specify default
      values for the column must all specify the same default, or an
      error will be reported.
     </para>

     <para><literal>CHECK</> constraints are merged in essentially the same way as
      columns: if multiple parent tables and/or the new table definition
      contain identically-named <literal>CHECK</> constraints, these
      constraints must all have the same check expression, or an error will be
      reported.  Constraints having the same name and expression will
      be merged into one copy.  A constraint marked <literal>NO INHERIT</> in a
      parent will not be considered.  Notice that an unnamed <literal>CHECK</>
      constraint in the new table will never be merged, since a unique name
      will always be chosen for it.
     </para>

     <para>
      Column <literal>STORAGE</> settings are also copied from parent tables.
     </para>

    </listitem>
   </varlistentry>

   <varlistentry>
    <term><literal>LIKE <replaceable>source_table</replaceable> [ <replaceable>like_option</replaceable> ... ]</literal></term>
    <listitem>
     <para>
      The <literal>LIKE</literal> clause specifies a table from which
      the new table automatically copies all column names, their data types,
      and their not-null constraints.
     </para>
     <para>
      Unlike <literal>INHERITS</literal>, the new table and original table
      are completely decoupled after creation is complete.  Changes to the
      original table will not be applied to the new table, and it is not
      possible to include data of the new table in scans of the original
      table.
     </para>
     <para>
      Default expressions for the copied column definitions will only be
      copied if <literal>INCLUDING DEFAULTS</literal> is specified.  The
      default behavior is to exclude default expressions, resulting in the
      copied columns in the new table having null defaults.
     </para>
     <para>
      Not-null constraints are always copied to the new table.
      <literal>CHECK</literal> constraints will be copied only if
      <literal>INCLUDING CONSTRAINTS</literal> is specified. 
      Indexes, <literal>PRIMARY KEY</>, and <literal>UNIQUE</> constraints
      on the original table will be created on the new table only if the
      <literal>INCLUDING INDEXES</literal> clause is specified.
      No distinction is made between column constraints and table
      constraints.
     </para>
     <para><literal>STORAGE</> settings for the copied column definitions will only
      be copied if <literal>INCLUDING STORAGE</literal> is specified.  The
      default behavior is to exclude <literal>STORAGE</> settings, resulting
      in the copied columns in the new table having type-specific default
      settings.  For more on <literal>STORAGE</> settings, see
      <xref linkend="storage-toast">.
     </para>
     <para>
      Comments for the copied columns, constraints, and indexes
      will only be copied if <literal>INCLUDING COMMENTS</literal>
      is specified. The default behavior is to exclude comments, resulting in
      the copied columns and constraints in the new table having no comments.
     </para>
     <para><literal>INCLUDING ALL</literal> is an abbreviated form of
      <literal>INCLUDING DEFAULTS INCLUDING CONSTRAINTS INCLUDING INDEXES INCLUDING STORAGE INCLUDING COMMENTS</literal>.
     </para>
     <para>
      Note also that unlike <literal>INHERITS</literal>, columns and
      constraints copied by <literal>LIKE</> are not merged with similarly
      named columns and constraints.
      If the same name is specified explicitly or in another
      <literal>LIKE</literal> clause, an error is signalled.
     </para>
     <para>
      The <literal>LIKE</literal> clause can also be used to copy columns from
      views, foreign tables, or composite types.  Inapplicable options (e.g., <literal>INCLUDING
      INDEXES</literal> from a view) are ignored.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><literal>CONSTRAINT <replaceable class="PARAMETER">constraint_name</replaceable></literal></term>
    <listitem>
     <para>
      An optional name for a column or table constraint.  If the
      constraint is violated, the constraint name is present in error messages,
      so constraint names like <literal>col must be positive</> can be used
      to communicate helpful constraint information to client applications.
      (Double-quotes are needed to specify constraint names that contain spaces.)
      If a constraint name is not specified, the system generates a name.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><literal>NOT NULL</></term>
    <listitem>
     <para>
      The column is not allowed to contain null values.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><literal>NULL</></term>
    <listitem>
     <para>
      The column is allowed to contain null values. This is the default.
     </para>

     <para>
      This clause is only provided for compatibility with
      non-standard SQL databases.  Its use is discouraged in new
      applications.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><literal>CHECK ( <replaceable class="PARAMETER">expression</replaceable> ) [ NO INHERIT ] </literal></term>
    <listitem>
     <para>
      The <literal>CHECK</> clause specifies an expression producing a
      Boolean result which new or updated rows must satisfy for an
      insert or update operation to succeed.  Expressions evaluating
      to TRUE or UNKNOWN succeed.  Should any row of an insert or
      update operation produce a FALSE result an error exception is
      raised and the insert or update does not alter the database.  A
      check constraint specified as a column constraint should
      reference that column's value only, while an expression
      appearing in a table constraint can reference multiple columns.
     </para>

     <para>
      Currently, <literal>CHECK</literal> expressions cannot contain
      subqueries nor refer to variables other than columns of the
      current row.
     </para>

     <para>
      A constraint marked with <literal>NO INHERIT</> will not propagate to
      child tables.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><literal>DEFAULT
    <replaceable>default_expr</replaceable></literal></term>
    <listitem>
     <para>
      The <literal>DEFAULT</> clause assigns a default data value for
      the column whose column definition it appears within.  The value
      is any variable-free expression (subqueries and cross-references
      to other columns in the current table are not allowed).  The
      data type of the default expression must match the data type of the
      column.
     </para>

     <para>
      The default expression will be used in any insert operation that
      does not specify a value for the column.  If there is no default
      for a column, then the default is null.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><literal>UNIQUE</> (column constraint)</term>
    <term><literal>UNIQUE ( <replaceable class="PARAMETER">column_name</replaceable> [, ... ] )</> (table constraint)</term>

    <listitem>
     <para>
      The <literal>UNIQUE</literal> constraint specifies that a
      group of one or more columns of a table can contain
      only unique values. The behavior of the unique table constraint
      is the same as that for column constraints, with the additional
      capability to span multiple columns.
     </para>

     <para>
      For the purpose of a unique constraint, null values are not
      considered equal.
     </para>

     <para>
      Each unique table constraint must name a set of columns that is
      different from the set of columns named by any other unique or
      primary key constraint defined for the table.  (Otherwise it
      would just be the same constraint listed twice.)
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><literal>PRIMARY KEY</> (column constraint)</term>
    <term><literal>PRIMARY KEY ( <replaceable class="PARAMETER">column_name</replaceable> [, ... ] )</> (table constraint)</term>
    <listitem>
     <para>
      The primary key constraint specifies that a column or columns of a table
      can contain only unique (non-duplicate), nonnull values.
      Technically, <literal>PRIMARY KEY</literal> is merely a
      combination of <literal>UNIQUE</> and <literal>NOT NULL</>, but
      identifying a set of columns as primary key also provides
      metadata about the design of the schema, as a primary key
      implies that other tables
      can rely on this set of columns as a unique identifier for rows.
     </para>

     <para>
      Only one primary key can be specified for a table, whether as a
      column constraint or a table constraint.
     </para>

     <para>
      The primary key constraint should name a set of columns that is
      different from other sets of columns named by any unique
      constraint defined for the same table.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry id="SQL-CREATETABLE-EXCLUDE">
    <term><literal>EXCLUDE [ USING <replaceable class="parameter">index_method</replaceable> ] ( <replaceable class="parameter">exclude_element</replaceable> WITH <replaceable class="parameter">operator</replaceable> [, ... ] ) <replaceable class="parameter">index_parameters</replaceable> [ WHERE ( <replaceable class="parameter">predicate</replaceable> ) ]</literal></term>
    <listitem>
     <para>
      The <literal>EXCLUDE</> clause defines an exclusion
      constraint, which guarantees that if
      any two rows are compared on the specified column(s) or
      expression(s) using the specified operator(s), not all of these
      comparisons will return <literal>TRUE</>.  If all of the
      specified operators test for equality, this is equivalent to a
      <literal>UNIQUE</> constraint, although an ordinary unique constraint
      will be faster.  However, exclusion constraints can specify
      constraints that are more general than simple equality.
      For example, you can specify a constraint that
      no two rows in the table contain overlapping circles
      (see <xref linkend="datatype-geometric">) by using the
      <literal>&amp;&amp;</> operator.
     </para>

     <para>
      Exclusion constraints are implemented using
      an index, so each specified operator must be associated with an
      appropriate operator class
      (see <xref linkend="indexes-opclass">) for the index access
      method <replaceable>index_method</>.
      The operators are required to be commutative.
      Each <replaceable class="parameter">exclude_element</replaceable>
      can optionally specify an operator class and/or ordering options;
      these are described fully under
      <xref linkend="sql-createindex">.
     </para>

     <para>
      The access method must support <literal>amgettuple</> (see <xref
      linkend="indexam">); at present this means <acronym>GIN</>
      cannot be used.  Although it's allowed, there is little point in using
      B-tree or hash indexes with an exclusion constraint, because this
      does nothing that an ordinary unique constraint doesn't do better.
      So in practice the access method will always be <acronym>GiST</> or
      <acronym>SP-GiST</>.
     </para>

     <para>
      The <replaceable class="parameter">predicate</> allows you to specify an
      exclusion constraint on a subset of the table; internally this creates a
      partial index. Note that parentheses are required around the predicate.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><literal>REFERENCES <replaceable class="parameter">reftable</replaceable> [ ( <replaceable class="parameter">refcolumn</replaceable> ) ] [ MATCH <replaceable class="parameter">matchtype</replaceable> ] [ ON DELETE <replaceable class="parameter">action</replaceable> ] [ ON UPDATE <replaceable class="parameter">action</replaceable> ]</literal> (column constraint)</term>

   <term><literal>FOREIGN KEY ( <replaceable class="parameter">column_name</replaceable> [, ... ] )
    REFERENCES <replaceable class="parameter">reftable</replaceable> [ ( <replaceable class="parameter">refcolumn</replaceable> [, ... ] ) ]
    [ MATCH <replaceable class="parameter">matchtype</replaceable> ]
    [ ON DELETE <replaceable class="parameter">action</replaceable> ]
    [ ON UPDATE <replaceable class="parameter">action</replaceable> ]</literal>
    (table constraint)</term>

    <listitem>
     <para>
      These clauses specify a foreign key constraint, which requires
      that a group of one or more columns of the new table must only
      contain values that match values in the referenced
      column(s) of some row of the referenced table.  If the <replaceable
      class="parameter">refcolumn</replaceable> list is omitted, the
      primary key of the <replaceable class="parameter">reftable</replaceable>
      is used.  The referenced columns must be the columns of a non-deferrable
      unique or primary key constraint in the referenced table.  Note that
      foreign key constraints cannot be defined between temporary tables and
      permanent tables.
     </para>

     <para>
      A value inserted into the referencing column(s) is matched against the
      values of the referenced table and referenced columns using the
      given match type.  There are three match types: <literal>MATCH
      FULL</>, <literal>MATCH PARTIAL</>, and <literal>MATCH
      SIMPLE</literal> (which is the default).  <literal>MATCH
      FULL</> will not allow one column of a multicolumn foreign key
      to be null unless all foreign key columns are null; if they are all
      null, the row is not required to have a match in the referenced table.
      <literal>MATCH SIMPLE</literal> allows any of the foreign key columns
      to be null; if any of them are null, the row is not required to have a
      match in the referenced table.
      <literal>MATCH PARTIAL</> is not yet implemented.
      (Of course, <literal>NOT NULL</> constraints can be applied to the
      referencing column(s) to prevent these cases from arising.)
     </para>

     <para>
      In addition, when the data in the referenced columns is changed,
      certain actions are performed on the data in this table's
      columns.  The <literal>ON DELETE</literal> clause specifies the
      action to perform when a referenced row in the referenced table is
      being deleted.  Likewise, the <literal>ON UPDATE</literal>
      clause specifies the action to perform when a referenced column
      in the referenced table is being updated to a new value. If the
      row is updated, but the referenced column is not actually
      changed, no action is done. Referential actions other than the
      <literal>NO ACTION</literal> check cannot be deferred, even if
      the constraint is declared deferrable. There are the following possible
      actions for each clause:

      <variablelist>
       <varlistentry>
        <term><literal>NO ACTION</literal></term>
        <listitem>
         <para>
          Produce an error indicating that the deletion or update
          would create a foreign key constraint violation.
          If the constraint is deferred, this
          error will be produced at constraint check time if there still
          exist any referencing rows.  This is the default action.
         </para>
        </listitem>
       </varlistentry>

       <varlistentry>
        <term><literal>RESTRICT</literal></term>
        <listitem>
         <para>
          Produce an error indicating that the deletion or update
          would create a foreign key constraint violation.
          This is the same as <literal>NO ACTION</literal> except that
          the check is not deferrable.
         </para>
        </listitem>
       </varlistentry>

       <varlistentry>
        <term><literal>CASCADE</literal></term>
        <listitem>
         <para>
          Delete any rows referencing the deleted row, or update the
          values of the referencing column(s) to the new values of the
          referenced columns, respectively.
         </para>
        </listitem>
       </varlistentry>

       <varlistentry>
        <term><literal>SET NULL</literal></term>
        <listitem>
         <para>
          Set the referencing column(s) to null.
         </para>
        </listitem>
       </varlistentry>

       <varlistentry>
        <term><literal>SET DEFAULT</literal></term>
        <listitem>
         <para>
          Set the referencing column(s) to their default values.
          (There must be a row in the referenced table matching the default
          values, if they are not null, or the operation will fail.)
         </para>
        </listitem>
       </varlistentry>
      </variablelist>
     </para>

     <para>
      If the referenced column(s) are changed frequently, it might be wise to
      add an index to the referencing column(s) so that referential actions
      associated with the foreign key constraint can be performed more
      efficiently.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><literal>DEFERRABLE</literal></term>
    <term><literal>NOT DEFERRABLE</literal></term>
    <listitem>
     <para>
      This controls whether the constraint can be deferred.  A
      constraint that is not deferrable will be checked immediately
      after every command.  Checking of constraints that are
      deferrable can be postponed until the end of the transaction
      (using the <xref linkend="sql-set-constraints"> command).
      <literal>NOT DEFERRABLE</literal> is the default.
      Currently, only <literal>UNIQUE</>, <literal>PRIMARY KEY</>,
      <literal>EXCLUDE</>, and
      <literal>REFERENCES</> (foreign key) constraints accept this
      clause.  <literal>NOT NULL</> and <literal>CHECK</> constraints are not
      deferrable.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><literal>INITIALLY IMMEDIATE</literal></term>
    <term><literal>INITIALLY DEFERRED</literal></term>
    <listitem>
     <para>
      If a constraint is deferrable, this clause specifies the default
      time to check the constraint.  If the constraint is
      <literal>INITIALLY IMMEDIATE</literal>, it is checked after each
      statement. This is the default.  If the constraint is
      <literal>INITIALLY DEFERRED</literal>, it is checked only at the
      end of the transaction.  The constraint check time can be
      altered with the <xref linkend="sql-set-constraints"> command.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><literal>WITH ( <replaceable class="PARAMETER">storage_parameter</replaceable> [= <replaceable class="PARAMETER">value</replaceable>] [, ... ] )</literal></term>
    <listitem>
     <para>
      This clause specifies optional storage parameters for a table or index;
      see <xref linkend="sql-createtable-storage-parameters"
      endterm="sql-createtable-storage-parameters-title"> for more
      information.  The <literal>WITH</> clause for a
      table can also include <literal>OIDS=TRUE</> (or just <literal>OIDS</>)
      to specify that rows of the new table
      should have OIDs (object identifiers) assigned to them, or
      <literal>OIDS=FALSE</> to specify that the rows should not have OIDs.
      If <literal>OIDS</> is not specified, the default setting depends upon
      the <xref linkend="guc-default-with-oids"> configuration parameter.
      (If the new table inherits from any tables that have OIDs, then
      <literal>OIDS=TRUE</> is forced even if the command says
      <literal>OIDS=FALSE</>.)
     </para>

     <para>
      If <literal>OIDS=FALSE</literal> is specified or implied, the new
      table does not store OIDs and no OID will be assigned for a row inserted
      into it. This is generally considered worthwhile, since it
      will reduce OID consumption and thereby postpone the wraparound
      of the 32-bit OID counter. Once the counter wraps around, OIDs
      can no longer be assumed to be unique, which makes them
      considerably less useful. In addition, excluding OIDs from a
      table reduces the space required to store the table on disk by
      4 bytes per row (on most machines), slightly improving performance.
     </para>

     <para>
      To remove OIDs from a table after it has been created, use <xref
      linkend="sql-altertable">.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><literal>WITH OIDS</></term>
    <term><literal>WITHOUT OIDS</></term>
    <listitem>
     <para>
      These are obsolescent syntaxes equivalent to <literal>WITH (OIDS)</>
      and <literal>WITH (OIDS=FALSE)</>, respectively.  If you wish to give
      both an <literal>OIDS</> setting and storage parameters, you must use
      the <literal>WITH ( ... )</> syntax; see above.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><literal>ON COMMIT</literal></term>
    <listitem>
     <para>
      The behavior of temporary tables at the end of a transaction
      block can be controlled using <literal>ON COMMIT</literal>.
      The three options are:

      <variablelist>
       <varlistentry>
        <term><literal>PRESERVE ROWS</literal></term>
        <listitem>
         <para>
          No special action is taken at the ends of transactions.
          This is the default behavior.
         </para>
        </listitem>
       </varlistentry>

       <varlistentry>
        <term><literal>DELETE ROWS</literal></term>
        <listitem>
         <para>
          All rows in the temporary table will be deleted at the end
          of each transaction block.  Essentially, an automatic <xref
          linkend="sql-truncate"> is done
          at each commit.
         </para>
        </listitem>
       </varlistentry>

       <varlistentry>
        <term><literal>DROP</literal></term>
        <listitem>
         <para>
          The temporary table will be dropped at the end of the current
          transaction block.
         </para>
        </listitem>
       </varlistentry>
      </variablelist></para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><literal>TABLESPACE <replaceable class="PARAMETER">tablespace_name</replaceable></literal></term>
    <listitem>
     <para>
      The <replaceable class="PARAMETER">tablespace_name</replaceable> is the name
      of the tablespace in which the new table is to be created.
      If not specified,
      <xref linkend="guc-default-tablespace"> is consulted, or
      <xref linkend="guc-temp-tablespaces"> if the table is temporary.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><literal>USING INDEX TABLESPACE <replaceable class="PARAMETER">tablespace_name</replaceable></literal></term>
    <listitem>
     <para>
      This clause allows selection of the tablespace in which the index
      associated with a <literal>UNIQUE</literal>, <literal>PRIMARY
      KEY</literal>, or <literal>EXCLUDE</> constraint will be created.
      If not specified,
      <xref linkend="guc-default-tablespace"> is consulted, or
      <xref linkend="guc-temp-tablespaces"> if the table is temporary.
     </para>
    </listitem>
   </varlistentry>

  </variablelist>

  <refsect2 id="SQL-CREATETABLE-storage-parameters">
   <title id="SQL-CREATETABLE-storage-parameters-title">Storage Parameters</title>

 <indexterm zone="sql-createtable-storage-parameters">
  <primary>storage parameters</primary>
 </indexterm>

   <para>
    The <literal>WITH</> clause can specify <firstterm>storage parameters</>
    for tables, and for indexes associated with a <literal>UNIQUE</literal>,
    <literal>PRIMARY KEY</literal>, or <literal>EXCLUDE</> constraint.
    Storage parameters for
    indexes are documented in <xref linkend="SQL-CREATEINDEX">.
    The storage parameters currently
    available for tables are listed below.  For each parameter, unless noted,
    there is an additional parameter with the same name prefixed with
    <literal>toast.</literal>, which can be used to control the behavior of the
    table's secondary <acronym>TOAST</> table, if any
    (see <xref linkend="storage-toast"> for more information about TOAST).
    Note that the TOAST table inherits the
    <literal>autovacuum_*</literal> values from its parent table, if there are
    no <literal>toast.autovacuum_*</literal> settings set.
   </para>

   <variablelist>

   <varlistentry>
    <term><literal>fillfactor</> (<type>integer</>)</term>
    <listitem>
     <para>
      The fillfactor for a table is a percentage between 10 and 100.
      100 (complete packing) is the default.  When a smaller fillfactor
      is specified, <command>INSERT</> operations pack table pages only
      to the indicated percentage; the remaining space on each page is
      reserved for updating rows on that page.  This gives <command>UPDATE</>
      a chance to place the updated copy of a row on the same page as the
      original, which is more efficient than placing it on a different page.
      For a table whose entries are never updated, complete packing is the
      best choice, but in heavily updated tables smaller fillfactors are
      appropriate.  This parameter cannot be set for TOAST tables.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><literal>autovacuum_enabled</>, <literal>toast.autovacuum_enabled</literal> (<type>boolean</>)</term>
    <listitem>
     <para>
     Enables or disables the autovacuum daemon on a particular table.
     If true, the autovacuum daemon will initiate a <command>VACUUM</> operation
     on a particular table when the number of updated or deleted tuples exceeds
     <literal>autovacuum_vacuum_threshold</> plus
     <literal>autovacuum_vacuum_scale_factor</> times the number of live tuples
     currently estimated to be in the relation.
     Similarly, it will initiate an <command>ANALYZE</> operation when the
     number of inserted, updated or deleted tuples exceeds
     <literal>autovacuum_analyze_threshold</> plus
     <literal>autovacuum_analyze_scale_factor</> times the number of live tuples
     currently estimated to be in the relation.
     If false, this table will not be autovacuumed, except to prevent
     transaction Id wraparound. See <xref linkend="vacuum-for-wraparound"> for
     more about wraparound prevention.
     Observe that this variable inherits its value from the <xref
     linkend="guc-autovacuum"> setting.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><literal>autovacuum_vacuum_threshold</>, <literal>toast.autovacuum_vacuum_threshold</literal> (<type>integer</>)</term>
    <listitem>
     <para>
     Minimum number of updated or deleted tuples before initiate a
     <command>VACUUM</> operation on a particular table.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><literal>autovacuum_vacuum_scale_factor</>, <literal>toast.autovacuum_vacuum_scale_factor</literal> (<type>float4</>)</term>
    <listitem>
     <para>
     Multiplier for <structfield>reltuples</> to add to
     <literal>autovacuum_vacuum_threshold</>.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><literal>autovacuum_analyze_threshold</> (<type>integer</>)</term>
    <listitem>
     <para>
     Minimum number of inserted, updated, or deleted tuples before initiate an
     <command>ANALYZE</> operation on a particular table.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><literal>autovacuum_analyze_scale_factor</> (<type>float4</>)</term>
    <listitem>
     <para>
     Multiplier for <structfield>reltuples</> to add to
     <literal>autovacuum_analyze_threshold</>.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><literal>autovacuum_vacuum_cost_delay</>, <literal>toast.autovacuum_vacuum_cost_delay</literal> (<type>integer</>)</term>
    <listitem>
     <para>
     Custom <xref linkend="guc-autovacuum-vacuum-cost-delay"> parameter.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><literal>autovacuum_vacuum_cost_limit</>, <literal>toast.autovacuum_vacuum_cost_limit</literal> (<type>integer</>)</term>
    <listitem>
     <para>
     Custom <xref linkend="guc-autovacuum-vacuum-cost-limit"> parameter.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><literal>autovacuum_freeze_min_age</>, <literal>toast.autovacuum_freeze_min_age</literal> (<type>integer</>)</term>
    <listitem>
     <para>
     Custom <xref linkend="guc-vacuum-freeze-min-age"> parameter. Note that
     autovacuum will ignore attempts to set a per-table
     <literal>autovacuum_freeze_min_age</> larger than the half system-wide
     <xref linkend="guc-autovacuum-freeze-max-age"> setting.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><literal>autovacuum_freeze_max_age</>, <literal>toast.autovacuum_freeze_max_age</literal> (<type>integer</>)</term>
    <listitem>
     <para>
     Custom <xref linkend="guc-autovacuum-freeze-max-age"> parameter. Note that
     autovacuum will ignore attempts to set a per-table
     <literal>autovacuum_freeze_max_age</> larger than the system-wide setting
     (it can only be set smaller). Note that while you can set
     <literal>autovacuum_freeze_max_age</> very small, or even zero, this is
     usually unwise since it will force frequent vacuuming.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><literal>autovacuum_freeze_table_age</literal>, <literal>toast.autovacuum_freeze_table_age</literal> (<type>integer</type>)</term>
    <listitem>
     <para>
      Custom <xref linkend="guc-vacuum-freeze-table-age"> parameter.
     </para>
    </listitem>
   </varlistentry>

   </variablelist>

  </refsect2>
 </refsect1>

 <refsect1 id="SQL-CREATETABLE-notes">
  <title>Notes</title>

    <para>
     Using OIDs in new applications is not recommended: where
     possible, using a <literal>SERIAL</literal> or other sequence
     generator as the table's primary key is preferred. However, if
     your application does make use of OIDs to identify specific
     rows of a table, it is recommended to create a unique constraint
     on the <structfield>oid</> column of that table, to ensure that
     OIDs in the table will indeed uniquely identify rows even after
     counter wraparound.  Avoid assuming that OIDs are unique across
     tables; if you need a database-wide unique identifier, use the
     combination of <structfield>tableoid</> and row OID for the
     purpose.
    </para>

    <tip>
     <para>
      The use of <literal>OIDS=FALSE</literal> is not recommended
      for tables with no primary key, since without either an OID or a
      unique data key, it is difficult to identify specific rows.
     </para>
    </tip>

    <para>
     <productname>PostgreSQL</productname> automatically creates an
     index for each unique constraint and primary key constraint to
     enforce uniqueness.  Thus, it is not necessary to create an
     index explicitly for primary key columns.  (See <xref
     linkend="sql-createindex"> for more information.)
    </para>

    <para>
     Unique constraints and primary keys are not inherited in the
     current implementation.  This makes the combination of
     inheritance and unique constraints rather dysfunctional.
    </para>

    <para>
     A table cannot have more than 1600 columns.  (In practice, the
     effective limit is usually lower because of tuple-length constraints.)
    </para>

 </refsect1>


 <refsect1 id="SQL-CREATETABLE-examples">
  <title>Examples</title>

  <para>
   Create table <structname>films</> and table
   <structname>distributors</>:

<programlisting>
CREATE TABLE films (
    code        char(5) CONSTRAINT firstkey PRIMARY KEY,
    title       varchar(40) NOT NULL,
    did         integer NOT NULL,
    date_prod   date,
    kind        varchar(10),
    len         interval hour to minute
);

CREATE TABLE distributors (
     did    integer PRIMARY KEY DEFAULT nextval('serial'),
     name   varchar(40) NOT NULL CHECK (name &lt;&gt; '')
);
</programlisting>
  </para>

  <para>
   Create a table with a 2-dimensional array:

<programlisting>
CREATE TABLE array_int (
    vector  int[][]
);
</programlisting>
  </para>

  <para>
   Define a unique table constraint for the table
   <literal>films</literal>.  Unique table constraints can be defined
   on one or more columns of the table:

<programlisting>
CREATE TABLE films (
    code        char(5),
    title       varchar(40),
    did         integer,
    date_prod   date,
    kind        varchar(10),
    len         interval hour to minute,
    CONSTRAINT production UNIQUE(date_prod)
);
</programlisting>
  </para>

  <para>
   Define a check column constraint:

<programlisting>
CREATE TABLE distributors (
    did     integer CHECK (did &gt; 100),
    name    varchar(40)
);
</programlisting>
  </para>

  <para>
   Define a check table constraint:

<programlisting>
CREATE TABLE distributors (
    did     integer,
    name    varchar(40)
    CONSTRAINT con1 CHECK (did &gt; 100 AND name &lt;&gt; '')
);
</programlisting>
  </para>

  <para>
   Define a primary key table constraint for the table
   <structname>films</>:

<programlisting>
CREATE TABLE films (
    code        char(5),
    title       varchar(40),
    did         integer,
    date_prod   date,
    kind        varchar(10),
    len         interval hour to minute,
    CONSTRAINT code_title PRIMARY KEY(code,title)
);
</programlisting>
  </para>

  <para>
   Define a primary key constraint for table
   <structname>distributors</>.  The following two examples are
   equivalent, the first using the table constraint syntax, the second
   the column constraint syntax:

<programlisting>
CREATE TABLE distributors (
    did     integer,
    name    varchar(40),
    PRIMARY KEY(did)
);

CREATE TABLE distributors (
    did     integer PRIMARY KEY,
    name    varchar(40)
);
</programlisting>
  </para>

  <para>
   Assign a literal constant default value for the column
   <literal>name</literal>, arrange for the default value of column
   <literal>did</literal> to be generated by selecting the next value
   of a sequence object, and make the default value of
   <literal>modtime</literal> be the time at which the row is
   inserted:

<programlisting>
CREATE TABLE distributors (
    name      varchar(40) DEFAULT 'Luso Films',
    did       integer DEFAULT nextval('distributors_serial'),
    modtime   timestamp DEFAULT current_timestamp
);
</programlisting>
  </para>

  <para>
   Define two <literal>NOT NULL</> column constraints on the table
   <classname>distributors</classname>, one of which is explicitly
   given a name:

<programlisting>
CREATE TABLE distributors (
    did     integer CONSTRAINT no_null NOT NULL,
    name    varchar(40) NOT NULL
);
</programlisting>
    </para>

    <para>
     Define a unique constraint for the <literal>name</literal> column:

<programlisting>
CREATE TABLE distributors (
    did     integer,
    name    varchar(40) UNIQUE
);
</programlisting>

     The same, specified as a table constraint:

<programlisting>
CREATE TABLE distributors (
    did     integer,
    name    varchar(40),
    UNIQUE(name)
);
</programlisting>
  </para>

  <para>
   Create the same table, specifying 70% fill factor for both the table
   and its unique index:

<programlisting>
CREATE TABLE distributors (
    did     integer,
    name    varchar(40),
    UNIQUE(name) WITH (fillfactor=70)
)
WITH (fillfactor=70);
</programlisting>
  </para>

  <para>
   Create table <structname>circles</> with an exclusion
   constraint that prevents any two circles from overlapping:

<programlisting>
CREATE TABLE circles (
    c circle,
    EXCLUDE USING gist (c WITH &amp;&amp;)
);
</programlisting>
  </para>

  <para>
   Create table <structname>cinemas</> in tablespace <structname>diskvol1</>:

<programlisting>
CREATE TABLE cinemas (
        id serial,
        name text,
        location text
) TABLESPACE diskvol1;
</programlisting>
  </para>

  <para>
   Create a composite type and a typed table:
<programlisting>
CREATE TYPE employee_type AS (name text, salary numeric);

CREATE TABLE employees OF employee_type (
    PRIMARY KEY (name),
    salary WITH OPTIONS DEFAULT 1000
);
</programlisting></para>
 </refsect1>

 <refsect1 id="SQL-CREATETABLE-compatibility">
  <title id="SQL-CREATETABLE-compatibility-title">Compatibility</title>

  <para>
   The <command>CREATE TABLE</command> command conforms to the
   <acronym>SQL</acronym> standard, with exceptions listed below.
  </para>

  <refsect2>
   <title>Temporary Tables</title>

   <para>
    Although the syntax of <literal>CREATE TEMPORARY TABLE</literal>
    resembles that of the SQL standard, the effect is not the same.  In the
    standard,
    temporary tables are defined just once and automatically exist (starting
    with empty contents) in every session that needs them.
    <productname>PostgreSQL</productname> instead
    requires each session to issue its own <literal>CREATE TEMPORARY
    TABLE</literal> command for each temporary table to be used.  This allows
    different sessions to use the same temporary table name for different
    purposes, whereas the standard's approach constrains all instances of a
    given temporary table name to have the same table structure.
   </para>

   <para>
    The standard's definition of the behavior of temporary tables is
    widely ignored.  <productname>PostgreSQL</productname>'s behavior
    on this point is similar to that of several other SQL databases.
   </para>

   <para>
    The SQL standard also distinguishes between global and local temporary
    tables, where a local temporary table has a separate set of contents for
    each SQL module within each session, though its definition is still shared
    across sessions.  Since <productname>PostgreSQL</productname> does not
    support SQL modules, this distinction is not relevant in
    <productname>PostgreSQL</productname>.
   </para>

   <para>
    For compatibility's sake, <productname>PostgreSQL</productname> will
    accept the <literal>GLOBAL</literal> and <literal>LOCAL</literal> keywords
    in a temporary table declaration, but they currently have no effect.
    Use of these keywords is discouraged, since future versions of
    <productname>PostgreSQL</productname> might adopt a more
    standard-compliant interpretation of their meaning.
   </para>

   <para>
    The <literal>ON COMMIT</literal> clause for temporary tables
    also resembles the SQL standard, but has some differences.
    If the <literal>ON COMMIT</> clause is omitted, SQL specifies that the
    default behavior is <literal>ON COMMIT DELETE ROWS</>.  However, the
    default behavior in <productname>PostgreSQL</productname> is
    <literal>ON COMMIT PRESERVE ROWS</literal>.  The <literal>ON COMMIT
    DROP</literal> option does not exist in SQL.
   </para>
  </refsect2>

  <refsect2>
   <title>Non-deferred Uniqueness Constraints</title>

   <para>
    When a <literal>UNIQUE</> or <literal>PRIMARY KEY</> constraint is
    not deferrable, <productname>PostgreSQL</productname> checks for
    uniqueness immediately whenever a row is inserted or modified.
    The SQL standard says that uniqueness should be enforced only at
    the end of the statement; this makes a difference when, for example,
    a single command updates multiple key values.  To obtain
    standard-compliant behavior, declare the constraint as
    <literal>DEFERRABLE</> but not deferred (i.e., <literal>INITIALLY
    IMMEDIATE</>).  Be aware that this can be significantly slower than
    immediate uniqueness checking.
   </para>
  </refsect2>

  <refsect2>
   <title>Column Check Constraints</title>

   <para>
    The SQL standard says that <literal>CHECK</> column constraints
    can only refer to the column they apply to; only <literal>CHECK</>
    table constraints can refer to multiple columns.
    <productname>PostgreSQL</productname> does not enforce this
    restriction; it treats column and table check constraints alike.
   </para>
  </refsect2>

  <refsect2>
   <title><literal>EXCLUDE</literal> Constraint</title>

   <para>
    The <literal>EXCLUDE</> constraint type is a
    <productname>PostgreSQL</productname> extension.
   </para>
  </refsect2>

  <refsect2>
   <title><literal>NULL</literal> <quote>Constraint</quote></title>

   <para>
    The <literal>NULL</> <quote>constraint</quote> (actually a
    non-constraint) is a <productname>PostgreSQL</productname>
    extension to the SQL standard that is included for compatibility with some
    other database systems (and for symmetry with the <literal>NOT
    NULL</literal> constraint).  Since it is the default for any
    column, its presence is simply noise.
   </para>
  </refsect2>

  <refsect2>
   <title>Inheritance</title>

   <para>
    Multiple inheritance via the <literal>INHERITS</literal> clause is
    a <productname>PostgreSQL</productname> language extension.
    SQL:1999 and later define single inheritance using a
    different syntax and different semantics.  SQL:1999-style
    inheritance is not yet supported by
    <productname>PostgreSQL</productname>.
   </para>
  </refsect2>

  <refsect2>
   <title>Zero-column Tables</title>

   <para>
    <productname>PostgreSQL</productname> allows a table of no columns
    to be created (for example, <literal>CREATE TABLE foo();</>).  This
    is an extension from the SQL standard, which does not allow zero-column
    tables.  Zero-column tables are not in themselves very useful, but
    disallowing them creates odd special cases for <command>ALTER TABLE
    DROP COLUMN</>, so it seems cleaner to ignore this spec restriction.
   </para>
  </refsect2>

  <refsect2>
   <title><literal>WITH</> Clause</title>

   <para>
    The <literal>WITH</> clause is a <productname>PostgreSQL</productname>
    extension; neither storage parameters nor OIDs are in the standard.
   </para>
  </refsect2>

  <refsect2>
   <title>Tablespaces</title>

   <para>
    The <productname>PostgreSQL</productname> concept of tablespaces is not
    part of the standard.  Hence, the clauses <literal>TABLESPACE</literal>
    and <literal>USING INDEX TABLESPACE</literal> are extensions.
   </para>
  </refsect2>

  <refsect2>
   <title>Typed Tables</title>

   <para>
    Typed tables implement a subset of the SQL standard.  According to
    the standard, a typed table has columns corresponding to the
    underlying composite type as well as one other column that is
    the <quote>self-referencing column</quote>.  PostgreSQL does not
    support these self-referencing columns explicitly, but the same
    effect can be had using the OID feature.
   </para>
  </refsect2>
 </refsect1>


 <refsect1>
  <title>See Also</title>

  <simplelist type="inline">
   <member><xref linkend="sql-altertable"></member>
   <member><xref linkend="sql-droptable"></member>
   <member><xref linkend="sql-createtableas"></member>
   <member><xref linkend="sql-createtablespace"></member>
   <member><xref linkend="sql-createtype"></member>
  </simplelist>
 </refsect1>
</refentry>
