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doc/src/sgml/ref/create_table.sgml
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Masahiko Sawada
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<!--
doc/src/sgml/ref/create_table.sgml
PostgreSQL documentation
-->

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

 <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>

 <refsynopsisdiv>
<synopsis>
CREATE [ <replaceable>persistence_mode</replaceable> ] TABLE [ IF NOT EXISTS ] <replaceable class="parameter">table_name</replaceable> ( [
  { <replaceable class="parameter">column_name</replaceable> <replaceable class="parameter">data_type</replaceable> [ <replaceable>column_storage</replaceable> ] [ <replaceable>column_compression</replaceable> ] [ COLLATE <replaceable class="parameter">collation</replaceable> ] [ <replaceable>column_constraint</replaceable> [ ... ] ]
    | <replaceable>table_constraint</replaceable>
    | LIKE <replaceable>source_table</replaceable> [ <replaceable>like_option</replaceable> ... ] }
    [, ... ]
] )
[ INHERITS ( <replaceable>parent_table</replaceable> [, ... ] ) ]
[ PARTITION BY { RANGE | LIST | HASH } ( { <replaceable class="parameter">column_name</replaceable> | ( <replaceable class="parameter">expression</replaceable> ) } [ COLLATE <replaceable class="parameter">collation</replaceable> ] [ <replaceable class="parameter">opclass</replaceable> ] [, ... ] ) ]
[ USING <replaceable class="parameter">method</replaceable> ]
[ WITH ( <replaceable class="parameter">storage_parameter</replaceable> [= <replaceable class="parameter">value</replaceable>] [, ... ] ) | WITHOUT OIDS ]
[ ON COMMIT { PRESERVE ROWS | DELETE ROWS | DROP } ]
[ TABLESPACE <replaceable class="parameter">tablespace_name</replaceable> ]

CREATE [ <replaceable>persistence_mode</replaceable> ] 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> }
    [, ... ]
) ]
[ PARTITION BY { RANGE | LIST | HASH } ( { <replaceable class="parameter">column_name</replaceable> | ( <replaceable class="parameter">expression</replaceable> ) } [ COLLATE <replaceable class="parameter">collation</replaceable> ] [ <replaceable class="parameter">opclass</replaceable> ] [, ... ] ) ]
[ USING <replaceable class="parameter">method</replaceable> ]
[ WITH ( <replaceable class="parameter">storage_parameter</replaceable> [= <replaceable class="parameter">value</replaceable>] [, ... ] ) | WITHOUT OIDS ]
[ ON COMMIT { PRESERVE ROWS | DELETE ROWS | DROP } ]
[ TABLESPACE <replaceable class="parameter">tablespace_name</replaceable> ]

CREATE [ <replaceable>persistence_mode</replaceable> ] TABLE [ IF NOT EXISTS ] <replaceable class="parameter">table_name</replaceable>
    PARTITION OF <replaceable class="parameter">parent_table</replaceable> [ (
  { <replaceable class="parameter">column_name</replaceable> [ WITH OPTIONS ] [ <replaceable class="parameter">column_constraint</replaceable> [ ... ] ]
    | <replaceable>table_constraint</replaceable> }
    [, ... ]
) ] { FOR VALUES <replaceable class="parameter">partition_bound_spec</replaceable> | DEFAULT }
[ PARTITION BY { RANGE | LIST | HASH } ( { <replaceable class="parameter">column_name</replaceable> | ( <replaceable class="parameter">expression</replaceable> ) } [ COLLATE <replaceable class="parameter">collation</replaceable> ] [ <replaceable class="parameter">opclass</replaceable> ] [, ... ] ) ]
[ USING <replaceable class="parameter">method</replaceable> ]
[ WITH ( <replaceable class="parameter">storage_parameter</replaceable> [= <replaceable class="parameter">value</replaceable>] [, ... ] ) | WITHOUT OIDS ]
[ ON COMMIT { PRESERVE ROWS | DELETE ROWS | DROP } ]
[ TABLESPACE <replaceable class="parameter">tablespace_name</replaceable> ]

<phrase>where <replaceable>persistence_mode</replaceable> is:</phrase>

{ [ GLOBAL | LOCAL ] { TEMPORARY | TEMP } } | UNLOGGED

<phrase>and <replaceable>column_storage</replaceable> is:</phrase>

STORAGE { PLAIN | EXTERNAL | EXTENDED | MAIN | DEFAULT }

<phrase>and <replaceable>column_compression</replaceable> is:</phrase>

COMPRESSION <replaceable>compression_method</replaceable>

<phrase>and <replaceable class="parameter">column_constraint</replaceable> is:</phrase>

[ CONSTRAINT <replaceable class="parameter">constraint_name</replaceable> ]
{ NOT NULL [ NO INHERIT ]  |
  NULL |
  CHECK ( <replaceable class="parameter">expression</replaceable> ) [ NO INHERIT ] |
  DEFAULT <replaceable>default_expr</replaceable> |
  GENERATED ALWAYS AS ( <replaceable>generation_expr</replaceable> ) [ STORED | VIRTUAL ] |
  GENERATED { ALWAYS | BY DEFAULT } AS IDENTITY [ ( <replaceable>sequence_options</replaceable> ) ] |
  UNIQUE [ NULLS [ NOT ] DISTINCT ] <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">referential_action</replaceable> ] [ ON UPDATE <replaceable class="parameter">referential_action</replaceable> ] }
[ DEFERRABLE | NOT DEFERRABLE ] [ INITIALLY DEFERRED | INITIALLY IMMEDIATE ] [ ENFORCED | NOT ENFORCED ]

<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 ] |
  NOT NULL <replaceable class="parameter">column_name</replaceable> [ NO INHERIT ] |
  UNIQUE [ NULLS [ NOT ] DISTINCT ] ( <replaceable class="parameter">column_name</replaceable> [, ... ] [, <replaceable class="parameter">column_name</replaceable> WITHOUT OVERLAPS ] ) <replaceable class="parameter">index_parameters</replaceable> |
  PRIMARY KEY ( <replaceable class="parameter">column_name</replaceable> [, ... ] [, <replaceable class="parameter">column_name</replaceable> WITHOUT OVERLAPS ] ) <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> [, ... ] [, PERIOD <replaceable class="parameter">column_name</replaceable> ] ) REFERENCES <replaceable class="parameter">reftable</replaceable> [ ( <replaceable class="parameter">refcolumn</replaceable> [, ... ] [, PERIOD <replaceable class="parameter">refcolumn</replaceable> ] ) ]
    [ MATCH FULL | MATCH PARTIAL | MATCH SIMPLE ] [ ON DELETE <replaceable
class="parameter">referential_action</replaceable> ] [ ON UPDATE <replaceable class="parameter">referential_action</replaceable> ] }
[ DEFERRABLE | NOT DEFERRABLE ] [ INITIALLY DEFERRED | INITIALLY IMMEDIATE ] [ ENFORCED | NOT ENFORCED ]

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

{ INCLUDING | EXCLUDING } { COMMENTS | COMPRESSION | CONSTRAINTS | DEFAULTS | GENERATED | IDENTITY | INDEXES | STATISTICS | STORAGE | ALL }

<phrase>and <replaceable class="parameter">partition_bound_spec</replaceable> is:</phrase>

IN ( <replaceable class="parameter">partition_bound_expr</replaceable> [, ...] ) |
FROM ( { <replaceable class="parameter">partition_bound_expr</replaceable> | MINVALUE | MAXVALUE } [, ...] )
  TO ( { <replaceable class="parameter">partition_bound_expr</replaceable> | MINVALUE | MAXVALUE } [, ...] ) |
WITH ( MODULUS <replaceable class="parameter">numeric_literal</replaceable>, REMAINDER <replaceable class="parameter">numeric_literal</replaceable> )

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

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

<phrase>and <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> ) } [ COLLATE <replaceable class="parameter">collation</replaceable> ] [ <replaceable class="parameter">opclass</replaceable> [ ( <replaceable class="parameter">opclass_parameter</replaceable> = <replaceable class="parameter">value</replaceable> [, ... ] ) ] ] [ ASC | DESC ] [ NULLS { FIRST | LAST } ]

<phrase>and <replaceable class="parameter">referential_action</replaceable> in a <literal>FOREIGN KEY</literal>/<literal>REFERENCES</literal> constraint is:</phrase>

{ NO ACTION | RESTRICT | CASCADE | SET NULL [ ( <replaceable class="parameter">column_name</replaceable> [, ... ] ) ] | SET DEFAULT [ ( <replaceable class="parameter">column_name</replaceable> [, ... ] ) ] }
</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>
   The durability characteristics of a table are governed by its persistence
   mode.  By default, the data will be persistent and crash-safe.
   For less stringent requirements and better performance, a table can be
   specified as <link linkend="sql-createtable-temporary">temporary</link>
   or <link linkend="sql-createtable-unlogged">unlogged</link>.
  </para>

  <para>
   If a schema name is given (for example, <literal>CREATE TABLE
   myschema.mytable ...</literal>) 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 relation (table, sequence, index, view,
   materialized 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 id="sql-createtable-temporary">
    <term><literal>TEMPORARY</literal> or <literal>TEMP</literal></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).  The default
      search_path includes the temporary schema first and so identically
      named existing permanent tables are not chosen for new plans
      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</command> on the temporary table after it is populated.
     </para>

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

   <varlistentry id="sql-createtable-unlogged">
    <term><literal>UNLOGGED</literal></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.
     </para>

     <para>
      If this is specified, any sequences created together with the unlogged
      table (for identity or serial columns) are also created as unlogged.
     </para>

     <para>
      This form is not supported for partitioned tables.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry id="sql-createtable-parms-if-not-exists">
    <term><literal>IF NOT EXISTS</literal></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 id="sql-createtable-parms-table-name">
    <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 id="sql-createtable-parms-type-name">
    <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 stand-alone composite type (that is,
      one created using <xref linkend="sql-createtype"/>) though it still
      produces a new composite type as well.  The table will have a
      dependency on the referenced type, meaning that cascaded alter and
      drop actions on that type will propagate to the table.
     </para>

     <para>
      A typed table always has the same column names and data types as the
      type it is derived from, so you cannot specify additional columns.
      But the <literal>CREATE TABLE</literal> command can add defaults
      and constraints to the table, as well as specify storage parameters.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry id="sql-createtable-parms-column-name">
    <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 id="sql-createtable-parms-data-type">
    <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 id="sql-createtable-parms-collate">
    <term><literal>COLLATE <replaceable>collation</replaceable></literal></term>
    <listitem>
     <para>
      The <literal>COLLATE</literal> 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 id="sql-createtable-parms-storage">
    <term>
     <literal>STORAGE { PLAIN | EXTERNAL | EXTENDED | MAIN | DEFAULT }</literal>
     <indexterm>
      <primary>TOAST</primary>
      <secondary>per-column storage settings</secondary>
     </indexterm>
    </term>
    <listitem>
     <para>
      This clause sets the storage mode for the column. This controls whether this
      column is held inline or in a secondary <acronym>TOAST</acronym> table,
      and whether the data should be compressed or not. <literal>PLAIN</literal>
      must be used for fixed-length values such as <type>integer</type> and is
      inline, uncompressed. <literal>MAIN</literal> is for inline, compressible
      data. <literal>EXTERNAL</literal> is for external, uncompressed data, and
      <literal>EXTENDED</literal> is for external, compressed data.
      Writing <literal>DEFAULT</literal> sets the storage mode to the default
      mode for the column's data type.  <literal>EXTENDED</literal> is the
      default for most data types that support non-<literal>PLAIN</literal>
      storage.
      Use of <literal>EXTERNAL</literal> will make substring operations on
      very large <type>text</type> and <type>bytea</type> values run faster,
      at the penalty of increased storage space.
      See <xref linkend="storage-toast"/> for more information.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry id="sql-createtable-parms-compression">
    <term><literal>COMPRESSION <replaceable class="parameter">compression_method</replaceable></literal></term>
    <listitem>
     <para>
      The <literal>COMPRESSION</literal> clause sets the compression method
      for the column.  Compression is supported only for variable-width data
      types, and is used only when the column's storage mode
      is <literal>main</literal> or <literal>extended</literal>.
      (See <xref linkend="sql-altertable"/> for information on
      column storage modes.) Setting this property for a partitioned table
      has no direct effect, because such tables have no storage of their own,
      but the configured value will be inherited by newly-created partitions.
      The supported compression methods are <literal>pglz</literal> and
      <literal>lz4</literal>.  (<literal>lz4</literal> is available only if
      <option>--with-lz4</option> was used when building
      <productname>PostgreSQL</productname>.)  In addition,
      <replaceable class="parameter">compression_method</replaceable>
      can be <literal>default</literal> to explicitly specify the default
      behavior, which is to consult the
      <xref linkend="guc-default-toast-compression"/> setting at the time of
      data insertion to determine the method to use.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry id="sql-createtable-parms-inherits">
    <term><literal>INHERITS ( <replaceable>parent_table</replaceable> [, ... ] )</literal></term>
    <listitem>
     <para>
      The optional <literal>INHERITS</literal> clause specifies a list of
      tables from which the new table automatically inherits all
      columns.  Parent tables can be plain tables or foreign tables.
     </para>

     <para>
      Use of <literal>INHERITS</literal> 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</literal> 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</literal> 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</literal> in a
      parent will not be considered.  Notice that an unnamed <literal>CHECK</literal>
      constraint in the new table will never be merged, since a unique name
      will always be chosen for it.
     </para>

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

     <para>
      If a column in the parent table is an identity column, that property is
      not inherited.  A column in the child table can be declared identity
      column if desired.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry id="sql-createtable-parms-partition-by">
    <term><literal>PARTITION BY { RANGE | LIST | HASH } ( { <replaceable class="parameter">column_name</replaceable> | ( <replaceable class="parameter">expression</replaceable> ) } [ <replaceable class="parameter">opclass</replaceable> ] [, ...] ) </literal></term>
    <listitem>
     <para>
      The optional <literal>PARTITION BY</literal> clause specifies a strategy
      of partitioning the table.  The table thus created is called a
      <firstterm>partitioned</firstterm> table.  The parenthesized list of
      columns or expressions forms the <firstterm>partition key</firstterm>
      for the table.  When using range or hash partitioning, the partition key
      can include multiple columns or expressions (up to 32, but this limit can
      be altered when building <productname>PostgreSQL</productname>), but for
      list partitioning, the partition key must consist of a single column or
      expression.
     </para>

     <para>
      Range and list partitioning require a btree operator class, while hash
      partitioning requires a hash operator class.  If no operator class is
      specified explicitly, the default operator class of the appropriate
      type will be used; if no default operator class exists, an error will
      be raised.  When hash partitioning is used, the operator class used
      must implement support function 2 (see <xref linkend="xindex-support"/>
      for details).
     </para>

     <para>
      A partitioned table is divided into sub-tables (called partitions),
      which are created using separate <literal>CREATE TABLE</literal> commands.
      The partitioned table is itself empty.  A data row inserted into the
      table is routed to a partition based on the value of columns or
      expressions in the partition key.  If no existing partition matches
      the values in the new row, an error will be reported.
     </para>

     <para>
      See <xref linkend="ddl-partitioning"/> for more discussion on table
      partitioning.
     </para>

    </listitem>
   </varlistentry>

   <varlistentry id="sql-createtable-partition">
    <term><literal>PARTITION OF <replaceable class="parameter">parent_table</replaceable> { FOR VALUES <replaceable class="parameter">partition_bound_spec</replaceable> | DEFAULT }</literal></term>
    <listitem>
     <para>
      Creates the table as a <firstterm>partition</firstterm> of the specified
      parent table. The table can be created either as a partition for specific
      values using <literal>FOR VALUES</literal> or as a default partition
      using <literal>DEFAULT</literal>.  Any indexes, constraints and
      user-defined row-level triggers that exist in the parent table are cloned
      on the new partition.
     </para>

     <para>
      The <replaceable class="parameter">partition_bound_spec</replaceable>
      must correspond to the partitioning method and partition key of the
      parent table, and must not overlap with any existing partition of that
      parent.  The form with <literal>IN</literal> is used for list partitioning,
      the form with <literal>FROM</literal> and <literal>TO</literal> is used
      for range partitioning, and the form with <literal>WITH</literal> is used
      for hash partitioning.
     </para>

     <para>
      <replaceable class="parameter">partition_bound_expr</replaceable> is
      any variable-free expression (subqueries, window functions, aggregate
      functions, and set-returning functions are not allowed).  Its data type
      must match the data type of the corresponding partition key column.
      The expression is evaluated once at table creation time, so it can
      even contain volatile expressions such as
      <literal><function>CURRENT_TIMESTAMP</function></literal>.
     </para>

     <para>
      When creating a list partition, <literal>NULL</literal> can be
      specified to signify that the partition allows the partition key
      column to be null.  However, there cannot be more than one such
      list partition for a given parent table.  <literal>NULL</literal>
      cannot be specified for range partitions.
     </para>

     <para>
      When creating a range partition, the lower bound specified with
      <literal>FROM</literal> is an inclusive bound, whereas the upper
      bound specified with <literal>TO</literal> is an exclusive bound.
      That is, the values specified in the <literal>FROM</literal> list
      are valid values of the corresponding partition key columns for this
      partition, whereas those in the <literal>TO</literal> list are
      not.  Note that this statement must be understood according to the
      rules of row-wise comparison (<xref linkend="row-wise-comparison"/>).
      For example, given <literal>PARTITION BY RANGE (x,y)</literal>, a partition
      bound <literal>FROM (1, 2) TO (3, 4)</literal>
      allows <literal>x=1</literal> with any <literal>y&gt;=2</literal>,
      <literal>x=2</literal> with any non-null <literal>y</literal>,
      and <literal>x=3</literal> with any <literal>y&lt;4</literal>.
     </para>

     <para>
      The special values <literal>MINVALUE</literal> and <literal>MAXVALUE</literal>
      may be used when creating a range partition to indicate that there
      is no lower or upper bound on the column's value. For example, a
      partition defined using <literal>FROM (MINVALUE) TO (10)</literal> allows
      any values less than 10, and a partition defined using
      <literal>FROM (10) TO (MAXVALUE)</literal> allows any values greater than
      or equal to 10.
     </para>

     <para>
      When creating a range partition involving more than one column, it
      can also make sense to use <literal>MAXVALUE</literal> as part of the lower
      bound, and <literal>MINVALUE</literal> as part of the upper bound. For
      example, a partition defined using
      <literal>FROM (0, MAXVALUE) TO (10, MAXVALUE)</literal> allows any rows
      where the first partition key column is greater than 0 and less than
      or equal to 10. Similarly, a partition defined using
      <literal>FROM ('a', MINVALUE) TO ('b', MINVALUE)</literal> allows any rows
      where the first partition key column starts with "a".
     </para>

     <para>
      Note that if <literal>MINVALUE</literal> or <literal>MAXVALUE</literal> is used for
      one column of a partitioning bound, the same value must be used for all
      subsequent columns.  For example, <literal>(10, MINVALUE, 0)</literal> is not
      a valid bound; you should write <literal>(10, MINVALUE, MINVALUE)</literal>.
     </para>

     <para>
      Also note that some element types, such as <literal>timestamp</literal>,
      have a notion of "infinity", which is just another value that can
      be stored. This is different from <literal>MINVALUE</literal> and
      <literal>MAXVALUE</literal>, which are not real values that can be stored,
      but rather they are ways of saying that the value is unbounded.
      <literal>MAXVALUE</literal> can be thought of as being greater than any
      other value, including "infinity" and <literal>MINVALUE</literal> as being
      less than any other value, including "minus infinity". Thus the range
      <literal>FROM ('infinity') TO (MAXVALUE)</literal> is not an empty range; it
      allows precisely one value to be stored &mdash; "infinity".
     </para>

     <para>
      If <literal>DEFAULT</literal> is specified, the table will be
      created as the default partition of the parent table.  This option
      is not available for hash-partitioned tables.  A partition key value
      not fitting into any other partition of the given parent will be
      routed to the default partition.
     </para>

     <para>
      When a table has an existing <literal>DEFAULT</literal> partition and
      a new partition is added to it, the default partition must
      be scanned to verify that it does not contain any rows which properly
      belong in the new partition.  If the default partition contains a
      large number of rows, this may be slow.  The scan will be skipped if
      the default partition is a foreign table or if it has a constraint which
      proves that it cannot contain rows which should be placed in the new
      partition.
     </para>

     <para>
      When creating a hash partition, a modulus and remainder must be specified.
      The modulus must be a positive integer, and the remainder must be a
      non-negative integer less than the modulus.  Typically, when initially
      setting up a hash-partitioned table, you should choose a modulus equal to
      the number of partitions and assign every table the same modulus and a
      different remainder (see examples, below).   However, it is not required
      that every partition have the same modulus, only that every modulus which
      occurs among the partitions of a hash-partitioned table is a factor of the
      next larger modulus.  This allows the number of partitions to be increased
      incrementally without needing to move all the data at once.  For example,
      suppose you have a hash-partitioned table with 8 partitions, each of which
      has modulus 8, but find it necessary to increase the number of partitions
      to 16.  You can detach one of the modulus-8 partitions, create two new
      modulus-16 partitions covering the same portion of the key space (one with
      a remainder equal to the remainder of the detached partition, and the
      other with a remainder equal to that value plus 8), and repopulate them
      with data.  You can then repeat this -- perhaps at a later time -- for
      each modulus-8 partition until none remain.  While this may still involve
      a large amount of data movement at each step, it is still better than
      having to create a whole new table and move all the data at once.
     </para>

     <para>
      A partition must have the same column names and types as the partitioned
      table to which it belongs. Modifications to the column names or types of
      a partitioned table will automatically propagate to all partitions.
      <literal>CHECK</literal> constraints will be inherited automatically by
      every partition, but an individual partition may specify additional
      <literal>CHECK</literal> constraints; additional constraints with the
      same name and condition as in the parent will be merged with the parent
      constraint.  Defaults may be specified separately for each partition.
      But note that a partition's default value is not applied when inserting
      a tuple through a partitioned table.
     </para>

     <para>
      Rows inserted into a partitioned table will be automatically routed to
      the correct partition.  If no suitable partition exists, an error will
      occur.
     </para>

     <para>
      Operations such as <command>TRUNCATE</command>
      which normally affect a table and all of its
      inheritance children will cascade to all partitions, but may also be
      performed on an individual partition.
     </para>

     <para>
      Note that creating a partition using <literal>PARTITION OF</literal>
      requires taking an <literal>ACCESS EXCLUSIVE</literal> lock on the
      parent partitioned table.  Likewise, dropping a partition
      with <command>DROP TABLE</command> requires taking
      an <literal>ACCESS EXCLUSIVE</literal> lock on the parent table.
      It is possible to use <link linkend="sql-altertable"><command>ALTER
      TABLE ATTACH/DETACH PARTITION</command></link> to perform these
      operations with a weaker lock, thus reducing interference with
      concurrent operations on the partitioned table.
     </para>

    </listitem>
   </varlistentry>

   <varlistentry id="sql-createtable-parms-like">
    <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>
      Also unlike <literal>INHERITS</literal>, columns and
      constraints copied by <literal>LIKE</literal> 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 signaled.
     </para>
     <para>
      The optional <replaceable>like_option</replaceable> clauses specify
      which additional properties of the original table to copy.  Specifying
      <literal>INCLUDING</literal> copies the property, specifying
      <literal>EXCLUDING</literal> omits the property.
      <literal>EXCLUDING</literal> is the default.  If multiple specifications
      are made for the same kind of object, the last one is used.  The
      available options are:

      <variablelist>
       <varlistentry id="sql-createtable-parms-like-opt-comments">
        <term><literal>INCLUDING COMMENTS</literal></term>
        <listitem>
         <para>
          Comments for the copied columns, check constraints,
          not-null constraints, indexes, and extended statistics will be
          copied.  The default behavior is to exclude comments, resulting in
          the corresponding objects in the new table having no
          comments.
         </para>
        </listitem>
       </varlistentry>

       <varlistentry id="sql-createtable-parms-like-opt-compression">
        <term><literal>INCLUDING COMPRESSION</literal></term>
        <listitem>
         <para>
          Compression method of the columns will be copied.  The default
          behavior is to exclude compression methods, resulting in columns
          having the default compression method.
         </para>
        </listitem>
       </varlistentry>

       <varlistentry id="sql-createtable-parms-like-opt-constraints">
        <term><literal>INCLUDING CONSTRAINTS</literal></term>
        <listitem>
         <para>
          <literal>CHECK</literal> constraints will be copied.  No distinction
          is made between column constraints and table constraints.  Not-null
          constraints are always copied to the new table.
         </para>
        </listitem>
       </varlistentry>

       <varlistentry id="sql-createtable-parms-like-opt-defaults">
        <term><literal>INCLUDING DEFAULTS</literal></term>
        <listitem>
         <para>
          Default expressions for the copied column definitions will be
          copied.  Otherwise, default expressions are not copied, resulting in
          the copied columns in the new table having null defaults.  Note that
          copying defaults that call database-modification functions, such as
          <function>nextval</function>, may create a functional linkage
          between the original and new tables.
         </para>
        </listitem>
       </varlistentry>

       <varlistentry id="sql-createtable-parms-like-opt-generated">
        <term><literal>INCLUDING GENERATED</literal></term>
        <listitem>
         <para>
          Any generation expressions as well as the stored/virtual choice of
          copied column definitions will be copied.  By default, new columns
          will be regular base columns.
         </para>
        </listitem>
       </varlistentry>

       <varlistentry id="sql-createtable-parms-like-opt-identity">
        <term><literal>INCLUDING IDENTITY</literal></term>
        <listitem>
         <para>
          Any identity specifications of copied column definitions will be
          copied.  A new sequence is created for each identity column of the
          new table, separate from the sequences associated with the old
          table.
         </para>
        </listitem>
       </varlistentry>

       <varlistentry id="sql-createtable-parms-like-opt-indexes">
        <term><literal>INCLUDING INDEXES</literal></term>
        <listitem>
         <para>
          Indexes, <literal>PRIMARY KEY</literal>, <literal>UNIQUE</literal>,
          and <literal>EXCLUDE</literal> constraints on the original table
          will be created on the new table.  Names for the new indexes and
          constraints are chosen according to the default rules, regardless of
          how the originals were named.  (This behavior avoids possible
          duplicate-name failures for the new indexes.)
         </para>
        </listitem>
       </varlistentry>

       <varlistentry id="sql-createtable-parms-like-opt-statistics">
        <term><literal>INCLUDING STATISTICS</literal></term>
        <listitem>
         <para>
          Extended statistics are copied to the new table.
         </para>
        </listitem>
       </varlistentry>

       <varlistentry id="sql-createtable-parms-like-opt-storage">
        <term><literal>INCLUDING STORAGE</literal></term>
        <listitem>
         <para>
          <literal>STORAGE</literal> settings for the copied column
          definitions will be copied.  The default behavior is to exclude
          <literal>STORAGE</literal> settings, resulting in the copied columns
          in the new table having type-specific default settings.  For more on
          <literal>STORAGE</literal> settings, see <xref
          linkend="storage-toast"/>.
         </para>
        </listitem>
       </varlistentry>

       <varlistentry id="sql-createtable-parms-like-opt-all">
        <term><literal>INCLUDING ALL</literal></term>
        <listitem>
         <para>
          <literal>INCLUDING ALL</literal> is an abbreviated form selecting
          all the available individual options.  (It could be useful to write
          individual <literal>EXCLUDING</literal> clauses after
          <literal>INCLUDING ALL</literal> to select all but some specific
          options.)
         </para>
        </listitem>
       </varlistentry>
      </variablelist>
     </para>

     <para>
      The <literal>LIKE</literal> clause can also be used to copy column
      definitions from views, foreign tables, or composite types.
      Inapplicable options (e.g., <literal>INCLUDING INDEXES</literal> from
      a view) are ignored.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry id="sql-createtable-parms-constraint">
    <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</literal> 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 id="sql-createtable-parms-not-null">
    <term><literal>NOT NULL [ NO INHERIT ] </literal></term>
    <listitem>
     <para>
      The column is not allowed to contain null values.
     </para>

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

   <varlistentry id="sql-createtable-parms-null">
    <term><literal>NULL</literal></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 id="sql-createtable-parms-check">
    <term><literal>CHECK ( <replaceable class="parameter">expression</replaceable> ) [ NO INHERIT ] </literal></term>
    <listitem>
     <para>
      The <literal>CHECK</literal> 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 (see <xref linkend="ddl-constraints-check-constraints"/>).
      The system column <structfield>tableoid</structfield>
      may be referenced, but not any other system column.
     </para>

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

     <para>
      When a table has multiple <literal>CHECK</literal> constraints,
      they will be tested for each row in alphabetical order by name,
      after checking <literal>NOT NULL</literal> constraints.
      (<productname>PostgreSQL</productname> versions before 9.5 did not honor any
      particular firing order for <literal>CHECK</literal> constraints.)
     </para>
    </listitem>
   </varlistentry>

   <varlistentry id="sql-createtable-parms-default">
    <term><literal>DEFAULT
    <replaceable>default_expr</replaceable></literal></term>
    <listitem>
     <para>
      The <literal>DEFAULT</literal> clause assigns a default data value for
      the column whose column definition it appears within.  The value
      is any variable-free expression (in particular, cross-references
      to other columns in the current table are not allowed).  Subqueries
      are not allowed either.  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 id="sql-createtable-parms-generated-stored">
    <term><literal>GENERATED ALWAYS AS ( <replaceable>generation_expr</replaceable> ) [ STORED | VIRTUAL ]</literal><indexterm><primary>generated column</primary></indexterm></term>
    <listitem>
     <para>
      This clause creates the column as a <firstterm>generated
      column</firstterm>.  The column cannot be written to, and when read the
      result of the specified expression will be returned.
     </para>

     <para>
      When <literal>VIRTUAL</literal> is specified, the column will be
      computed when it is read, and it will not occupy any storage.  When
      <literal>STORED</literal> is specified, the column will be computed on
      write and will be stored on disk.  <literal>VIRTUAL</literal> is the
      default.
     </para>

     <para>
      The generation expression can refer to other columns in the table, but
      not other generated columns.  Any functions and operators used must be
      immutable.  References to other tables are not allowed.
     </para>

     <para>
      A virtual generated column cannot have a user-defined type, and the
      generation expression of a virtual generated column must not reference
      user-defined functions or types, that is, it can only use built-in
      functions or types.  This applies also indirectly, such as for functions
      or types that underlie operators or casts.  (This restriction does not
      exist for stored generated columns.)
     </para>
    </listitem>
   </varlistentry>

   <varlistentry id="sql-createtable-parms-generated-identity">
    <term><literal>GENERATED { ALWAYS | BY DEFAULT } AS IDENTITY [ ( <replaceable>sequence_options</replaceable> ) ]</literal></term>
    <listitem>
     <para>
      This clause creates the column as an <firstterm>identity
      column</firstterm>.  It will have an implicit sequence attached to it
      and in newly-inserted rows the column will automatically have values
      from the sequence assigned to it.
      Such a column is implicitly <literal>NOT NULL</literal>.
     </para>

     <para>
      The clauses <literal>ALWAYS</literal> and <literal>BY DEFAULT</literal>
      determine how explicitly user-specified values are handled in
      <command>INSERT</command> and <command>UPDATE</command> commands.
     </para>

     <para>
      In an <command>INSERT</command> command, if <literal>ALWAYS</literal> is
      selected, a user-specified value is only accepted if the
      <command>INSERT</command> statement specifies <literal>OVERRIDING SYSTEM
      VALUE</literal>.  If <literal>BY DEFAULT</literal> is selected, then the
      user-specified value takes precedence.  See <xref linkend="sql-insert"/>
      for details.  (In the <command>COPY</command> command, user-specified
      values are always used regardless of this setting.)
     </para>

     <para>
      In an <command>UPDATE</command> command, if <literal>ALWAYS</literal> is
      selected, any update of the column to any value other than
      <literal>DEFAULT</literal> will be rejected.  If <literal>BY
      DEFAULT</literal> is selected, the column can be updated normally.
      (There is no <literal>OVERRIDING</literal> clause for the
      <command>UPDATE</command> command.)
     </para>

     <para>
      The optional <replaceable>sequence_options</replaceable> clause can
      be used to override the parameters of the sequence.  The available
      options include those shown for <xref linkend="sql-createsequence"/>,
      plus <literal>SEQUENCE NAME <replaceable>name</replaceable></literal>,
      <literal>LOGGED</literal>, and <literal>UNLOGGED</literal>, which
      allow selection of the name and persistence level of the
      sequence.  Without <literal>SEQUENCE NAME</literal>, the system
      chooses an unused name for the sequence.
      Without <literal>LOGGED</literal> or <literal>UNLOGGED</literal>,
      the sequence will have the same persistence level as the table.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry id="sql-createtable-parms-unique">
    <term><literal>UNIQUE [ NULLS [ NOT ] DISTINCT ]</literal> (column constraint)</term>
    <term><literal>UNIQUE [ NULLS [ NOT ] DISTINCT ] ( <replaceable class="parameter">column_name</replaceable> [, ... ] [, <replaceable class="parameter">column_name</replaceable> WITHOUT OVERLAPS ] )</literal>
    <optional> <literal>INCLUDE ( <replaceable class="parameter">column_name</replaceable> [, ...])</literal> </optional> (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 a unique table constraint
      is the same as that of a unique column constraint, with the
      additional capability to span multiple columns.  The constraint
      therefore enforces that any two rows must differ in at least one
      of these columns.
     </para>

     <para>
      If the <literal>WITHOUT OVERLAPS</literal> option is specified for the
      last column, then that column is checked for overlaps instead of
      equality.  In that case, the other columns of the constraint will allow
      duplicates so long as the duplicates don't overlap in the
      <literal>WITHOUT OVERLAPS</literal> column.  (This is sometimes called a
      temporal key, if the column is a range of dates or timestamps, but
      <productname>PostgreSQL</productname> allows ranges over any base type.)
      In effect, such a constraint is enforced with an <literal>EXCLUDE</literal>
      constraint rather than a <literal>UNIQUE</literal> constraint.  So for
      example <literal>UNIQUE (id, valid_at WITHOUT OVERLAPS)</literal> behaves
      like <literal>EXCLUDE USING GIST (id WITH =, valid_at WITH
      &amp;&amp;)</literal>.  The <literal>WITHOUT OVERLAPS</literal> column
      must have a range or multirange type.  Empty ranges/multiranges are
      not permitted.  The non-<literal>WITHOUT OVERLAPS</literal> columns of
      the constraint can be any type that can be compared for equality in a
      GiST index.  By default, only range types are supported, but you can use
      other types by adding the <xref linkend="btree-gist"/> extension (which
      is the expected way to use this feature).
     </para>

     <para>
      For the purpose of a unique constraint, null values are not
      considered equal, unless <literal>NULLS NOT DISTINCT</literal> is
      specified.
     </para>

     <para>
      Each unique constraint should 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, redundant
      unique constraints will be discarded.)
     </para>

     <para>
      When establishing a unique constraint for a multi-level partition
      hierarchy, all the columns in the partition key of the target
      partitioned table, as well as those of all its descendant partitioned
      tables, must be included in the constraint definition.
     </para>

     <para>
      Adding a unique constraint will automatically create a unique btree
      index on the column or group of columns used in the constraint.  But if
      the constraint includes a <literal>WITHOUT OVERLAPS</literal> clause, it
      will use a GiST index.  The created index has the same name as the
      unique constraint.
     </para>

     <para>
      The optional <literal>INCLUDE</literal> clause adds to that index
      one or more columns that are simply <quote>payload</quote>: uniqueness
      is not enforced on them, and the index cannot be searched on the basis
      of those columns.  However they can be retrieved by an index-only scan.
      Note that although the constraint is not enforced on included columns,
      it still depends on them.  Consequently, some operations on such columns
      (e.g., <literal>DROP COLUMN</literal>) can cause cascaded constraint and
      index deletion.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry id="sql-createtable-parms-primary-key">
    <term><literal>PRIMARY KEY</literal> (column constraint)</term>
    <term><literal>PRIMARY KEY ( <replaceable class="parameter">column_name</replaceable> [, ... ] [, <replaceable class="parameter">column_name</replaceable> WITHOUT OVERLAPS ] )</literal>
    <optional> <literal>INCLUDE ( <replaceable class="parameter">column_name</replaceable> [, ...])</literal> </optional> (table constraint)</term>
    <listitem>
     <para>
      The <literal>PRIMARY KEY</literal> constraint specifies that a column or
      columns of a table can contain only unique (non-duplicate), nonnull
      values. 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 the set of columns named by any unique
      constraint defined for the same table.  (Otherwise, the unique
      constraint is redundant and will be discarded.)
     </para>

     <para>
      <literal>PRIMARY KEY</literal> enforces the same data constraints as
      a combination of <literal>UNIQUE</literal> and <literal>NOT
      NULL</literal>.  However,
      identifying a set of columns as the primary key also provides metadata
      about the design of the schema, since a primary key implies that other
      tables can rely on this set of columns as a unique identifier for rows.
     </para>

     <para>
      When placed on a partitioned table, <literal>PRIMARY KEY</literal>
      constraints share the restrictions previously described
      for <literal>UNIQUE</literal> constraints.
     </para>

     <para>
      Adding a <literal>PRIMARY KEY</literal> constraint will automatically
      create a unique btree index on the column or group of columns used in
      the constraint, or GiST if <literal>WITHOUT OVERLAPS</literal> was
      specified.
     </para>

     <para>
      The optional <literal>INCLUDE</literal> clause adds to that index
      one or more columns that are simply <quote>payload</quote>: uniqueness
      is not enforced on them, and the index cannot be searched on the basis
      of those columns.  However they can be retrieved by an index-only scan.
      Note that although the constraint is not enforced on included columns,
      it still depends on them.  Consequently, some operations on such columns
      (e.g., <literal>DROP COLUMN</literal>) can cause cascaded constraint and
      index deletion.
     </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</literal> 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</literal>.  If all of the
      specified operators test for equality, this is equivalent to a
      <literal>UNIQUE</literal> 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;</literal> operator.
      The operator(s) are required to be commutative.
     </para>

     <para>
      Exclusion constraints are implemented using
      an index that has the same name as the constraint, 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</replaceable>.
      Each <replaceable class="parameter">exclude_element</replaceable>
      defines a column of the index, so it can optionally specify a collation,
      an operator class, operator class parameters, and/or ordering options;
      these are described fully under <xref linkend="sql-createindex"/>.
     </para>

     <para>
      The access method must support <literal>amgettuple</literal> (see <xref
      linkend="indexam"/>); at present this means <acronym>GIN</acronym>
      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</acronym> or
      <acronym>SP-GiST</acronym>.
     </para>

     <para>
      The <replaceable class="parameter">predicate</replaceable> 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>

     <para>
      When establishing an exclusion constraint for a multi-level partition
      hierarchy, all the columns in the partition key of the target
      partitioned table, as well as those of all its descendant partitioned
      tables, must be included in the constraint definition.  Additionally,
      those columns must be compared using the equality operator.  These
      restrictions ensure that potentially-conflicting rows will exist in the
      same partition.  The constraint may also refer to other columns which
      are not a part of any partition key, which can be compared using any
      appropriate operator.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry id="sql-createtable-parms-references">
    <term><literal>REFERENCES <replaceable class="parameter">reftable</replaceable> [ ( <replaceable class="parameter">refcolumn</replaceable> ) ] [ MATCH <replaceable class="parameter">matchtype</replaceable> ] [ ON DELETE <replaceable class="parameter">referential_action</replaceable> ] [ ON UPDATE <replaceable class="parameter">referential_action</replaceable> ]</literal> (column constraint)</term>

   <term><literal>FOREIGN KEY ( <replaceable class="parameter">column_name</replaceable> [, ... ] [, PERIOD <replaceable class="parameter">column_name</replaceable> ] )
    REFERENCES <replaceable class="parameter">reftable</replaceable> [ ( <replaceable class="parameter">refcolumn</replaceable> [, ... ] [, PERIOD <replaceable class="parameter">refcolumn</replaceable> ] ) ]
    [ MATCH <replaceable class="parameter">matchtype</replaceable> ]
    [ ON DELETE <replaceable class="parameter">referential_action</replaceable> ]
    [ ON UPDATE <replaceable class="parameter">referential_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.  Otherwise, the <replaceable class="parameter">refcolumn</replaceable>
      list must refer to the columns of a non-deferrable unique or primary key
      constraint or be the columns of a non-partial unique index.
     </para>

     <para>
      If the last column is marked with <literal>PERIOD</literal>, it is
      treated in a special way.  While the non-<literal>PERIOD</literal>
      columns are compared for equality (and there must be at least one of
      them), the <literal>PERIOD</literal> column is not.  Instead, the
      constraint is considered satisfied if the referenced table has matching
      records (based on the non-<literal>PERIOD</literal> parts of the key)
      whose combined <literal>PERIOD</literal> values completely cover the
      referencing record's.  In other words, the reference must have a
      referent for its entire duration.  This column must be a range or
      multirange type.  In addition, the referenced table must have a primary
      key or unique constraint declared with <literal>WITHOUT
      OVERLAPS</literal>. Finally, if the foreign key has a PERIOD
      <replaceable class="parameter">column_name</replaceable> specification
      the corresponding <replaceable class="parameter">refcolumn</replaceable>,
      if present, must also be marked <literal>PERIOD</literal>.  If the
      <replaceable class="parameter">refcolumn</replaceable> clause is omitted,
      and thus the reftable's primary key constraint chosen, the primary key
      must have its final column marked <literal>WITHOUT OVERLAPS</literal>.
     </para>

     <para>
      For each pair of referencing and referenced column, if they are of a
      collatable data type, then the collations must either be both
      deterministic or else both the same.  This ensures that both columns
      have a consistent notion of equality.
     </para>

     <para>
      The user
      must have <literal>REFERENCES</literal> permission on the referenced
      table (either the whole table, or the specific referenced columns).  The
      addition of a foreign key constraint requires a
      <literal>SHARE ROW EXCLUSIVE</literal> lock on 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>, <literal>MATCH PARTIAL</literal>, and <literal>MATCH
      SIMPLE</literal> (which is the default).  <literal>MATCH
      FULL</literal> 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</literal> is not yet implemented.
      (Of course, <literal>NOT NULL</literal> 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 are executed as part of
      the data changing command, even if the constraint is deferred.  There
      are the following possible actions for each clause:

      <variablelist>
       <varlistentry id="sql-createtable-parms-references-refact-no-action">
        <term><literal>NO ACTION</literal></term>
        <listitem>
         <para>
          Produce an error if 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 id="sql-createtable-parms-references-refact-restrict">
        <term><literal>RESTRICT</literal></term>
        <listitem>
         <para>
          Produce an error if a row to be deleted or updated matches a row in
          the referencing table.  This prevents the action even if the state
          after the action would not violate the foreign key constraint.  In
          particular, it prevents updates of referenced rows to values that
          are distinct but compare as equal.  (But it does not prevent
          <quote>no-op</quote> updates that update a column to the same
          value.)
         </para>

         <para>
          In a temporal foreign key, this option is not supported.
         </para>
        </listitem>
       </varlistentry>

       <varlistentry id="sql-createtable-parms-references-refact-cascade">
        <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>

         <para>
          In a temporal foreign key, this option is not supported.
         </para>
        </listitem>
       </varlistentry>

       <varlistentry id="sql-createtable-parms-references-refact-set-null">
        <term><literal>SET NULL [ ( <replaceable>column_name</replaceable> [, ... ] ) ]</literal></term>
        <listitem>
         <para>
          Set all of the referencing columns, or a specified subset of the
          referencing columns, to null. A subset of columns can only be
          specified for <literal>ON DELETE</literal> actions.
         </para>

         <para>
          In a temporal foreign key, this option is not supported.
         </para>
        </listitem>
       </varlistentry>

       <varlistentry id="sql-createtable-parms-references-refact-set-default">
        <term><literal>SET DEFAULT [ ( <replaceable>column_name</replaceable> [, ... ] ) ]</literal></term>
        <listitem>
         <para>
          Set all of the referencing columns, or a specified subset of the
          referencing columns, to their default values. A subset of columns
          can only be specified for <literal>ON DELETE</literal> actions.
          (There must be a row in the referenced table matching the default
          values, if they are not null, or the operation will fail.)
         </para>

         <para>
          In a temporal foreign key, this option is not supported.
         </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 id="sql-createtable-parms-deferrable">
    <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 <link linkend="sql-set-constraints"><command>SET CONSTRAINTS</command></link> command).
      <literal>NOT DEFERRABLE</literal> is the default.
      Currently, only <literal>UNIQUE</literal>, <literal>PRIMARY KEY</literal>,
      <literal>EXCLUDE</literal>, and
      <literal>REFERENCES</literal> (foreign key) constraints accept this
      clause.  <literal>NOT NULL</literal> and <literal>CHECK</literal> constraints are not
      deferrable.  Note that deferrable constraints cannot be used as
      conflict arbiters in an <command>INSERT</command> statement that
      includes an <literal>ON CONFLICT</literal> clause.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry id="sql-createtable-parms-initially">
    <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 <link linkend="sql-set-constraints"><command>SET CONSTRAINTS</command></link> command.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry id="sql-createtable-parms-enforced">
    <term><literal>ENFORCED</literal></term>
    <term><literal>NOT ENFORCED</literal></term>
    <listitem>
     <para>
      When the constraint is <literal>ENFORCED</literal>, then the database
      system will ensure that the constraint is satisfied, by checking the
      constraint at appropriate times (after each statement or at the end of
      the transaction, as appropriate).  That is the default.  If the
      constraint is <literal>NOT ENFORCED</literal>, the database system will
      not check the constraint.  It is then up to the application code to
      ensure that the constraints are satisfied.  The database system might
      still assume that the data actually satisfies the constraint for
      optimization decisions where this does not affect the correctness of the
      result.
     </para>

     <para>
      <literal>NOT ENFORCED</literal> constraints can be useful as
      documentation if the actual checking of the constraint at run time is
      too expensive.
     </para>

     <para>
      This is currently only supported for foreign key and <literal>CHECK</literal>
      constraints.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry id="sql-createtable-method">
    <term><literal>USING <replaceable class="parameter">method</replaceable></literal></term>
    <listitem>
     <para>
      This optional clause specifies the table access method to use to store
      the contents for the new table; the method needs be an access method of
      type <literal>TABLE</literal>. See <xref linkend="tableam"/> for more
      information.  If this option is not specified, the default table access
      method is chosen for the new table. See <xref
      linkend="guc-default-table-access-method"/> for more information.
     </para>
     <para>
      When creating a partition, the table access method is the access method
      of its partitioned table, if set.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry id="sql-createtable-parms-with">
    <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"/> below for more
      information.  For backward-compatibility the <literal>WITH</literal>
      clause for a table can also include <literal>OIDS=FALSE</literal> to
      specify that rows of the new table should not contain OIDs (object
      identifiers), <literal>OIDS=TRUE</literal> is not supported anymore.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry id="sql-createtable-parms-without-oids">
    <term><literal>WITHOUT OIDS</literal></term>
    <listitem>
     <para>
      This is backward-compatible syntax for declaring a table
      <literal>WITHOUT OIDS</literal>, creating a table <literal>WITH
      OIDS</literal> is not supported anymore.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry id="sql-createtable-parms-on-commit">
    <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 id="sql-createtable-parms-on-commit-preserve-rows">
        <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 id="sql-createtable-parms-on-commit-delete-rows">
        <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 <link
          linkend="sql-truncate"><command>TRUNCATE</command></link> is done
          at each commit.  When used on a partitioned table, this
          is not cascaded to its partitions.
         </para>
        </listitem>
       </varlistentry>

       <varlistentry id="sql-createtable-parms-on-commit-drop">
        <term><literal>DROP</literal></term>
        <listitem>
         <para>
          The temporary table will be dropped at the end of the current
          transaction block.  When used on a partitioned table, this action
          drops its partitions and when used on tables with inheritance
          children, it drops the dependent children.
         </para>
        </listitem>
       </varlistentry>
      </variablelist></para>
    </listitem>
   </varlistentry>

   <varlistentry id="sql-createtable-tablespace">
    <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.  For
      partitioned tables, since no storage is required for the table itself,
      the tablespace specified overrides <literal>default_tablespace</literal>
      as the default tablespace to use for any newly created partitions when no
      other tablespace is explicitly specified.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry id="sql-createtable-parms-using-index-tablespace">
    <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</literal> 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" xreflabel="Storage Parameters">
   <title>Storage Parameters</title>

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

   <para>
    The <literal>WITH</literal> clause can specify <firstterm>storage parameters</firstterm>
    for tables, and for indexes associated with a <literal>UNIQUE</literal>,
    <literal>PRIMARY KEY</literal>, or <literal>EXCLUDE</literal> constraint.
    Storage parameters for
    indexes are documented in <xref linkend="sql-createindex"/>.
    The storage parameters currently
    available for tables are listed below.  For many of these parameters, as
    shown, there is an additional parameter with the same name prefixed with
    <literal>toast.</literal>, which controls the behavior of the
    table's secondary <acronym>TOAST</acronym> table, if any
    (see <xref linkend="storage-toast"/> for more information about TOAST).
    If a table parameter value is set and the
    equivalent <literal>toast.</literal> parameter is not, the TOAST table
    will use the table's parameter value.
    Specifying these parameters for partitioned tables is not supported,
    but you may specify them for individual leaf partitions.
   </para>

   <variablelist>

    <varlistentry id="reloption-fillfactor" xreflabel="fillfactor">
    <term><varname>fillfactor</varname> (<type>integer</type>)
    <indexterm>
     <primary><varname>fillfactor</varname> storage parameter</primary>
    </indexterm>
    </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</command> 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</command>
      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, and makes <link linkend="storage-hot">heap-only tuple
      updates</link> more likely.
      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 id="reloption-toast-tuple-target" xreflabel="toast_tuple_target">
    <term><literal>toast_tuple_target</literal> (<type>integer</type>)
    <indexterm>
     <primary><varname>toast_tuple_target</varname> storage parameter</primary>
    </indexterm>
    </term>
    <listitem>
     <para>
      The toast_tuple_target specifies the minimum tuple length required before
      we try to compress and/or move long column values into TOAST tables, and
      is also the target length we try to reduce the length below once toasting
      begins. This affects columns marked as External (for move),
      Main (for compression), or Extended (for both) and applies only to new
      tuples. There is no effect on existing rows.
      By default this parameter is set to allow at least 4 tuples per block,
      which with the default block size will be 2040 bytes. Valid values are
      between 128 bytes and the (block size - header), by default 8160 bytes.
      Changing this value may not be useful for very short or very long rows.
      Note that the default setting is often close to optimal, and
      it is possible that setting this parameter could have negative
      effects in some cases.
      This parameter cannot be set for TOAST tables.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry id="reloption-parallel-workers" xreflabel="parallel_workers">
    <term><literal>parallel_workers</literal> (<type>integer</type>)
     <indexterm>
     <primary><varname>parallel_workers</varname> storage parameter</primary>
    </indexterm>
    </term>
    <listitem>
     <para>
      This sets the number of workers that should be used to assist a parallel
      scan of this table.  If not set, the system will determine a value based
      on the relation size.  The actual number of workers chosen by the planner
      or by utility statements that use parallel scans may be less, for example
      due to the setting of <xref linkend="guc-max-worker-processes"/>.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry id="reloption-autovacuum-enabled" xreflabel="autovacuum_enabled">
    <term><literal>autovacuum_enabled</literal>, <literal>toast.autovacuum_enabled</literal> (<type>boolean</type>)
    <indexterm>
     <primary><varname>autovacuum_enabled</varname> storage parameter</primary>
    </indexterm>
    </term>
    <listitem>
     <para>
     Enables or disables the autovacuum daemon for a particular table.
     If true, the autovacuum daemon will perform automatic <command>VACUUM</command>
     and/or <command>ANALYZE</command> operations on this table following the rules
     discussed in <xref linkend="autovacuum"/>.
     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.
     Note that the autovacuum daemon does not run at all (except to prevent
     transaction ID wraparound) if the <xref linkend="guc-autovacuum"/>
     parameter is false; setting individual tables' storage parameters does
     not override that.  Therefore there is seldom much point in explicitly
     setting this storage parameter to <literal>true</literal>, only
     to <literal>false</literal>.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry id="reloption-vacuum-index-cleanup" xreflabel="vacuum_index_cleanup">
    <term><literal>vacuum_index_cleanup</literal>, <literal>toast.vacuum_index_cleanup</literal> (<type>enum</type>)
    <indexterm>
     <primary><varname>vacuum_index_cleanup</varname> storage parameter</primary>
    </indexterm>
    </term>
    <listitem>
     <para>
      Forces or disables index cleanup when <command>VACUUM</command>
      is run on this table.  The default value is
      <literal>AUTO</literal>.  With <literal>OFF</literal>, index
      cleanup is disabled, with <literal>ON</literal> it is enabled,
      and with <literal>AUTO</literal> a decision is made dynamically,
      each time <command>VACUUM</command> runs.  The dynamic behavior
      allows <command>VACUUM</command> to avoid needlessly scanning
      indexes to remove very few dead tuples.  Forcibly disabling all
      index cleanup can speed up <command>VACUUM</command> very
      significantly, but may also lead to severely bloated indexes if
      table modifications are frequent.  The
      <literal>INDEX_CLEANUP</literal> parameter of <link
       linkend="sql-vacuum"><command>VACUUM</command></link>, if
      specified, overrides the value of this option.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry id="reloption-vacuum-truncate" xreflabel="vacuum_truncate">
    <term><literal>vacuum_truncate</literal>, <literal>toast.vacuum_truncate</literal> (<type>boolean</type>)
    <indexterm>
     <primary><varname>vacuum_truncate</varname></primary>
     <secondary>storage parameter</secondary>
    </indexterm>
    </term>
    <listitem>
     <para>
      Per-table value for <xref linkend="guc-vacuum-truncate"/> parameter.  The
      <literal>TRUNCATE</literal> parameter of
      <link linkend="sql-vacuum"><command>VACUUM</command></link>, if
      specified, overrides the value of this option.
     </para>
    </listitem>
   </varlistentry>

  <varlistentry id="reloption-autovacuum-parallel-workers" xreflabel="autovacuum_parallel_workers">
    <term><literal>autovacuum_parallel_workers</literal> (<type>integer</type>)
    <indexterm>
     <primary><varname>autovacuum_parallel_workers</varname> storage parameter</primary>
    </indexterm>
    </term>
    <listitem>
      <para>
       Per-table value for <xref linkend="guc-autovacuum-max-parallel-workers"/>
       parameter. If -1 is specified, <varname>autovacuum_max_parallel_workers</varname>
       value will be used. If set to 0, parallel vacuum is disabled for
       this table. The default value is -1.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry id="reloption-autovacuum-vacuum-threshold" xreflabel="autovacuum_vacuum_threshold">
    <term><literal>autovacuum_vacuum_threshold</literal>, <literal>toast.autovacuum_vacuum_threshold</literal> (<type>integer</type>)
    <indexterm>
     <primary><varname>autovacuum_vacuum_threshold</varname></primary>
     <secondary>storage parameter</secondary>
    </indexterm>
    </term>
    <listitem>
     <para>
      Per-table value for <xref linkend="guc-autovacuum-vacuum-threshold"/>
      parameter.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry id="reloption-autovacuum-vacuum-max-threshold" xreflabel="autovacuum_vacuum_max_threshold">
    <term><literal>autovacuum_vacuum_max_threshold</literal>, <literal>toast.autovacuum_vacuum_max_threshold</literal> (<type>integer</type>)
    <indexterm>
     <primary><varname>autovacuum_vacuum_max_threshold</varname></primary>
     <secondary>storage parameter</secondary>
    </indexterm>
    </term>
   <listitem>
    <para>
     Per-table value for <xref linkend="guc-autovacuum-vacuum-max-threshold"/>
     parameter.
    </para>
   </listitem>
  </varlistentry>

   <varlistentry id="reloption-autovacuum-vacuum-scale-factor" xreflabel="autovacuum_vacuum_scale_factor">
    <term><literal>autovacuum_vacuum_scale_factor</literal>, <literal>toast.autovacuum_vacuum_scale_factor</literal> (<type>floating point</type>)
    <indexterm>
     <primary><varname>autovacuum_vacuum_scale_factor</varname> </primary>
     <secondary>storage parameter</secondary>
    </indexterm>
    </term>
    <listitem>
     <para>
      Per-table value for <xref linkend="guc-autovacuum-vacuum-scale-factor"/>
      parameter.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry id="reloption-autovacuum-vacuum-insert-threshold" xreflabel="autovacuum_vacuum_insert_threshold">
    <term><literal>autovacuum_vacuum_insert_threshold</literal>, <literal>toast.autovacuum_vacuum_insert_threshold</literal> (<type>integer</type>)
    <indexterm>
     <primary><varname>autovacuum_vacuum_insert_threshold</varname></primary>
     <secondary>storage parameter</secondary>
    </indexterm>
    </term>
    <listitem>
     <para>
      Per-table value for <xref linkend="guc-autovacuum-vacuum-insert-threshold"/>
      parameter.  The special value of -1 may be used to disable insert vacuums on the table.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry id="reloption-autovacuum-vacuum-insert-scale-factor" xreflabel="autovacuum_vacuum_insert_scale_factor">
    <term><literal>autovacuum_vacuum_insert_scale_factor</literal>, <literal>toast.autovacuum_vacuum_insert_scale_factor</literal> (<type>floating point</type>)
    <indexterm>
     <primary><varname>autovacuum_vacuum_insert_scale_factor</varname> </primary>
     <secondary>storage parameter</secondary>
    </indexterm>
    </term>
    <listitem>
     <para>
      Per-table value for <xref linkend="guc-autovacuum-vacuum-insert-scale-factor"/>
      parameter.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry id="reloption-autovacuum-analyze-threshold" xreflabel="autovacuum_analyze_threshold">
    <term><literal>autovacuum_analyze_threshold</literal> (<type>integer</type>)
    <indexterm>
     <primary><varname>autovacuum_analyze_threshold</varname></primary>
     <secondary>storage parameter</secondary>
    </indexterm>
    </term>
    <listitem>
     <para>
      Per-table value for <xref linkend="guc-autovacuum-analyze-threshold"/>
      parameter.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry id="reloption-autovacuum-analyze-scale-factor" xreflabel="autovacuum_analyze_scale_factor">
    <term><literal>autovacuum_analyze_scale_factor</literal> (<type>floating point</type>)
    <indexterm>
     <primary><varname>autovacuum_analyze_scale_factor</varname></primary>
     <secondary>storage parameter</secondary>
    </indexterm>
    </term>
    <listitem>
     <para>
      Per-table value for <xref linkend="guc-autovacuum-analyze-scale-factor"/>
      parameter.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry id="reloption-autovacuum-vacuum-cost-delay" xreflabel="autovacuum_vacuum_cost_delay">
    <term><literal>autovacuum_vacuum_cost_delay</literal>, <literal>toast.autovacuum_vacuum_cost_delay</literal> (<type>floating point</type>)
    <indexterm>
     <primary><varname>autovacuum_vacuum_cost_delay</varname></primary>
     <secondary>storage parameter</secondary>
    </indexterm>
    </term>
    <listitem>
     <para>
      Per-table value for <xref linkend="guc-autovacuum-vacuum-cost-delay"/>
      parameter.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry id="reloption-autovacuum-vacuum-cost-limit" xreflabel="autovacuum_vacuum_cost_limit">
    <term><literal>autovacuum_vacuum_cost_limit</literal>, <literal>toast.autovacuum_vacuum_cost_limit</literal> (<type>integer</type>)
    <indexterm>
     <primary><varname>autovacuum_vacuum_cost_limit</varname></primary>
     <secondary>storage parameter</secondary>
    </indexterm>
    </term>
    <listitem>
     <para>
      Per-table value for <xref linkend="guc-autovacuum-vacuum-cost-limit"/>
      parameter.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry id="reloption-autovacuum-freeze-min-age" xreflabel="autovacuum_freeze_min_age">
    <term><literal>autovacuum_freeze_min_age</literal>, <literal>toast.autovacuum_freeze_min_age</literal> (<type>integer</type>)
    <indexterm>
     <primary><varname>autovacuum_freeze_min_age</varname> storage parameter</primary>
    </indexterm>
    </term>
    <listitem>
     <para>
      Per-table value for <xref linkend="guc-vacuum-freeze-min-age"/>
      parameter.  Note that autovacuum will ignore
      per-table <literal>autovacuum_freeze_min_age</literal> parameters that are
      larger than half the
      system-wide <xref linkend="guc-autovacuum-freeze-max-age"/> setting.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry id="reloption-autovacuum-freeze-max-age" xreflabel="autovacuum_freeze_max_age">
    <term><literal>autovacuum_freeze_max_age</literal>, <literal>toast.autovacuum_freeze_max_age</literal> (<type>integer</type>)
    <indexterm>
     <primary><varname>autovacuum_freeze_max_age</varname></primary>
     <secondary>storage parameter</secondary>
    </indexterm>
    </term>
    <listitem>
     <para>
      Per-table value for <xref linkend="guc-autovacuum-freeze-max-age"/>
      parameter.  Note that autovacuum will ignore
      per-table <literal>autovacuum_freeze_max_age</literal> parameters that are
      larger than the system-wide setting (it can only be set smaller).
     </para>
    </listitem>
   </varlistentry>

   <varlistentry id="reloption-autovacuum-freeze-table-age" xreflabel="autovacuum_freeze_table_age">
    <term><literal>autovacuum_freeze_table_age</literal>, <literal>toast.autovacuum_freeze_table_age</literal> (<type>integer</type>)
    <indexterm>
     <primary><varname>autovacuum_freeze_table_age</varname> storage parameter</primary>
    </indexterm>
    </term>
    <listitem>
     <para>
      Per-table value for <xref linkend="guc-vacuum-freeze-table-age"/>
      parameter.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry id="reloption-autovacuum-multixact-freeze-min-age" xreflabel="autovacuum_multixact_freeze_min_age">
    <term><literal>autovacuum_multixact_freeze_min_age</literal>, <literal>toast.autovacuum_multixact_freeze_min_age</literal> (<type>integer</type>)
    <indexterm>
     <primary><varname>autovacuum_multixact_freeze_min_age</varname> storage parameter</primary>
    </indexterm>
    </term>
    <listitem>
     <para>
      Per-table value for <xref linkend="guc-vacuum-multixact-freeze-min-age"/>
      parameter.  Note that autovacuum will ignore
      per-table <literal>autovacuum_multixact_freeze_min_age</literal> parameters
      that are larger than half the
      system-wide <xref linkend="guc-autovacuum-multixact-freeze-max-age"/>
      setting.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry id="reloption-autovacuum-multixact-freeze-max-age" xreflabel="autovacuum_multixact_freeze_max_age">
    <term><literal>autovacuum_multixact_freeze_max_age</literal>, <literal>toast.autovacuum_multixact_freeze_max_age</literal> (<type>integer</type>)
    <indexterm>
     <primary><varname>autovacuum_multixact_freeze_max_age</varname></primary>
     <secondary>storage parameter</secondary>
    </indexterm>
    </term>
    <listitem>
     <para>
      Per-table value
      for <xref linkend="guc-autovacuum-multixact-freeze-max-age"/> parameter.
      Note that autovacuum will ignore
      per-table <literal>autovacuum_multixact_freeze_max_age</literal> parameters
      that are larger than the system-wide setting (it can only be set
      smaller).
     </para>
    </listitem>
   </varlistentry>

   <varlistentry id="reloption-autovacuum-multixact-freeze-table-age" xreflabel="autovacuum_multixact_freeze_table_age">
    <term><literal>autovacuum_multixact_freeze_table_age</literal>, <literal>toast.autovacuum_multixact_freeze_table_age</literal> (<type>integer</type>)
    <indexterm>
     <primary><varname>autovacuum_multixact_freeze_table_age</varname> storage parameter</primary>
    </indexterm>
    </term>
    <listitem>
     <para>
      Per-table value
      for <xref linkend="guc-vacuum-multixact-freeze-table-age"/> parameter.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry id="reloption-log-autovacuum-min-duration" xreflabel="log_autovacuum_min_duration">
    <term><literal>log_autovacuum_min_duration</literal>, <literal>toast.log_autovacuum_min_duration</literal> (<type>integer</type>)
    <indexterm>
     <primary><varname>log_autovacuum_min_duration</varname></primary>
     <secondary>storage parameter</secondary>
    </indexterm>
    </term>
    <listitem>
     <para>
      Per-table value for <xref linkend="guc-log-autovacuum-min-duration"/>
      parameter.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry id="reloption-log-autoanalyze-min-duration" xreflabel="log_autoanalyze_min_duration">
    <term><literal>log_autoanalyze_min_duration</literal> (<type>integer</type>)
    <indexterm>
     <primary><varname>log_autoanalyze_min_duration</varname></primary>
     <secondary>storage parameter</secondary>
    </indexterm>
    </term>
    <listitem>
     <para>
      Per-table value for <xref linkend="guc-log-autoanalyze-min-duration"/>
      parameter.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry id="reloption-vacuum-max-eager-freeze-failure-rate" xreflabel="vacuum_max_eager_freeze_failure_rate">
    <term><literal>vacuum_max_eager_freeze_failure_rate</literal>, <literal>toast.vacuum_max_eager_freeze_failure_rate</literal> (<type>floating point</type>)
    <indexterm>
     <primary><varname>vacuum_max_eager_freeze_failure_rate</varname></primary>
     <secondary>storage parameter</secondary>
    </indexterm>
    </term>
    <listitem>
     <para>
      Per-table value for <xref linkend="guc-vacuum-max-eager-freeze-failure-rate"/>
      parameter.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry id="reloption-user-catalog-table" xreflabel="user_catalog_table">
    <term><literal>user_catalog_table</literal> (<type>boolean</type>)
    <indexterm>
     <primary><varname>user_catalog_table</varname> storage parameter</primary>
    </indexterm>
    </term>
    <listitem>
     <para>
      Declare the table as an additional catalog table for purposes of
      logical replication. See
      <xref linkend="logicaldecoding-capabilities"/> for details.
      This parameter cannot be set for TOAST tables.
     </para>
    </listitem>
   </varlistentry>

   </variablelist>

  </refsect2>
 </refsect1>

 <refsect1 id="sql-createtable-notes">
  <title>Notes</title>
    <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</structname> and table
   <structname>distributors</structname>:

<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 GENERATED BY DEFAULT AS IDENTITY,
     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</structname>:

<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</structname>.  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</literal> 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</structname> 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</structname> in tablespace <structname>diskvol1</structname>:

<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>

  <para>
   Create a range partitioned table:
<programlisting>
CREATE TABLE measurement (
    logdate         date NOT NULL,
    peaktemp        int,
    unitsales       int
) PARTITION BY RANGE (logdate);
</programlisting></para>

  <para>
   Create a range partitioned table with multiple columns in the partition key:
<programlisting>
CREATE TABLE measurement_year_month (
    logdate         date NOT NULL,
    peaktemp        int,
    unitsales       int
) PARTITION BY RANGE (EXTRACT(YEAR FROM logdate), EXTRACT(MONTH FROM logdate));
</programlisting></para>

  <para>
   Create a list partitioned table:
<programlisting>
CREATE TABLE cities (
    city_id      bigserial NOT NULL,
    name         text NOT NULL,
    population   bigint
) PARTITION BY LIST (left(lower(name), 1));
</programlisting></para>

  <para>
   Create a hash partitioned table:
<programlisting>
CREATE TABLE orders (
    order_id     bigint NOT NULL,
    cust_id      bigint NOT NULL,
    status       text
) PARTITION BY HASH (order_id);
</programlisting></para>

  <para>
   Create partition of a range partitioned table:
<programlisting>
CREATE TABLE measurement_y2016m07
    PARTITION OF measurement (
    unitsales DEFAULT 0
) FOR VALUES FROM ('2016-07-01') TO ('2016-08-01');
</programlisting></para>

  <para>
   Create a few partitions of a range partitioned table with multiple
   columns in the partition key:
<programlisting>
CREATE TABLE measurement_ym_older
    PARTITION OF measurement_year_month
    FOR VALUES FROM (MINVALUE, MINVALUE) TO (2016, 11);

CREATE TABLE measurement_ym_y2016m11
    PARTITION OF measurement_year_month
    FOR VALUES FROM (2016, 11) TO (2016, 12);

CREATE TABLE measurement_ym_y2016m12
    PARTITION OF measurement_year_month
    FOR VALUES FROM (2016, 12) TO (2017, 01);

CREATE TABLE measurement_ym_y2017m01
    PARTITION OF measurement_year_month
    FOR VALUES FROM (2017, 01) TO (2017, 02);
</programlisting></para>

  <para>
   Create partition of a list partitioned table:
<programlisting>
CREATE TABLE cities_ab
    PARTITION OF cities (
    CONSTRAINT city_id_nonzero CHECK (city_id != 0)
) FOR VALUES IN ('a', 'b');
</programlisting></para>

  <para>
   Create partition of a list partitioned table that is itself further
   partitioned and then add a partition to it:
<programlisting>
CREATE TABLE cities_ab
    PARTITION OF cities (
    CONSTRAINT city_id_nonzero CHECK (city_id != 0)
) FOR VALUES IN ('a', 'b') PARTITION BY RANGE (population);

CREATE TABLE cities_ab_10000_to_100000
    PARTITION OF cities_ab FOR VALUES FROM (10000) TO (100000);
</programlisting></para>

  <para>
   Create partitions of a hash partitioned table:
<programlisting>
CREATE TABLE orders_p1 PARTITION OF orders
    FOR VALUES WITH (MODULUS 4, REMAINDER 0);
CREATE TABLE orders_p2 PARTITION OF orders
    FOR VALUES WITH (MODULUS 4, REMAINDER 1);
CREATE TABLE orders_p3 PARTITION OF orders
    FOR VALUES WITH (MODULUS 4, REMAINDER 2);
CREATE TABLE orders_p4 PARTITION OF orders
    FOR VALUES WITH (MODULUS 4, REMAINDER 3);
</programlisting></para>

  <para>
   Create a default partition:
<programlisting>
CREATE TABLE cities_partdef
    PARTITION OF cities DEFAULT;
</programlisting></para>
 </refsect1>

 <refsect1 id="sql-createtable-compatibility" xreflabel="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</literal> clause is omitted, SQL specifies that the
    default behavior is <literal>ON COMMIT DELETE ROWS</literal>.  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</literal> or <literal>PRIMARY KEY</literal> 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</literal> but not deferred (i.e., <literal>INITIALLY
    IMMEDIATE</literal>).  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</literal> column constraints
    can only refer to the column they apply to; only <literal>CHECK</literal>
    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</literal> constraint type is a
    <productname>PostgreSQL</productname> extension.
   </para>
  </refsect2>

  <refsect2>
   <title>Foreign Key Constraints</title>

   <para>
    The ability to specify column lists in the foreign key actions
    <literal>SET DEFAULT</literal> and <literal>SET NULL</literal> is a
    <productname>PostgreSQL</productname> extension.
   </para>

   <para>
    It is a <productname>PostgreSQL</productname> extension that a
    foreign key constraint may reference columns of a unique index instead of
    columns of a primary key or unique constraint.
   </para>
  </refsect2>

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

   <para>
    The <literal>NULL</literal> <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>Constraint Naming</title>

   <para>
    The SQL standard says that table and domain constraints must have names
    that are unique across the schema containing the table or domain.
    <productname>PostgreSQL</productname> is laxer: it only requires
    constraint names to be unique across the constraints attached to a
    particular table or domain.  However, this extra freedom does not exist
    for index-based constraints (<literal>UNIQUE</literal>,
    <literal>PRIMARY KEY</literal>, and <literal>EXCLUDE</literal>
    constraints), because the associated index is named the same as the
    constraint, and index names must be unique across all relations within
    the same schema.
   </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();</literal>).  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</command>, so it seems cleaner to ignore this spec restriction.
   </para>
  </refsect2>

  <refsect2>
   <title>Multiple Identity Columns</title>

   <para>
    <productname>PostgreSQL</productname> allows a table to have more than one
    identity column.  The standard specifies that a table can have at most one
    identity column.  This is relaxed mainly to give more flexibility for
    doing schema changes or migrations.  Note that
    the <command>INSERT</command> command supports only one override clause
    that applies to the entire statement, so having multiple identity columns
    with different behaviors is not well supported.
   </para>
  </refsect2>

  <refsect2>
   <title>Generated Columns</title>

   <para>
    The options <literal>STORED</literal> and <literal>VIRTUAL</literal> are
    not standard but are also used by other SQL implementations.  The SQL
    standard does not specify the storage of generated columns.
   </para>
  </refsect2>

  <refsect2>
   <title><literal>LIKE</literal> Clause</title>

   <para>
    While a <literal>LIKE</literal> clause exists in the SQL standard, many of the
    options that <productname>PostgreSQL</productname> accepts for it are not
    in the standard, and some of the standard's options are not implemented
    by <productname>PostgreSQL</productname>.
   </para>
  </refsect2>

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

   <para>
    The <literal>WITH</literal> clause is a <productname>PostgreSQL</productname>
    extension; storage parameters are not 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>.
    <productname>PostgreSQL</productname> does not support self-referencing
    columns explicitly.
   </para>
  </refsect2>

  <refsect2>
   <title><literal>PARTITION BY</literal> Clause</title>

   <para>
    The <literal>PARTITION BY</literal> clause is a
    <productname>PostgreSQL</productname> extension.
   </para>
  </refsect2>

  <refsect2>
   <title><literal>PARTITION OF</literal> Clause</title>

   <para>
    The <literal>PARTITION OF</literal> clause is a
    <productname>PostgreSQL</productname> extension.
   </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>