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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 [ [ GLOBAL | LOCAL ] { TEMPORARY | TEMP } | UNLOGGED ] TABLE [ IF NOT EXISTS ] <replaceable class="parameter">table_name</replaceable> ( [
{ <replaceable class="parameter">column_name</replaceable> <replaceable class="parameter">data_type</replaceable> [ COLLATE <replaceable>collation</replaceable> ] [ <replaceable class="parameter">column_constraint</replaceable> [ ... ] ]
| <replaceable>table_constraint</replaceable>
| LIKE <replaceable>source_table</replaceable> [ <replaceable>like_option</replaceable> ... ] }
[, ... ]
] )
[ INHERITS ( <replaceable>parent_table</replaceable> [, ... ] ) ]
[ 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 [ [ GLOBAL | LOCAL ] { TEMPORARY | TEMP } | UNLOGGED ] TABLE [ IF NOT EXISTS ] <replaceable class="parameter">table_name</replaceable>
OF <replaceable class="parameter">type_name</replaceable> [ (
{ <replaceable class="parameter">column_name</replaceable> [ WITH OPTIONS ] [ <replaceable class="parameter">column_constraint</replaceable> [ ... ] ]
| <replaceable>table_constraint</replaceable> }
[, ... ]
) ]
[ 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 [ [ GLOBAL | LOCAL ] { TEMPORARY | TEMP } | UNLOGGED ] 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 class="parameter">column_constraint</replaceable> is:</phrase>
[ CONSTRAINT <replaceable class="parameter">constraint_name</replaceable> ]
{ NOT NULL |
NULL |
CHECK ( <replaceable class="parameter">expression</replaceable> ) [ NO INHERIT ] |
DEFAULT <replaceable>default_expr</replaceable> |
GENERATED ALWAYS AS ( <replaceable>generation_expr</replaceable> ) STORED |
GENERATED { ALWAYS | BY DEFAULT } AS IDENTITY [ ( <replaceable>sequence_options</replaceable> ) ] |
UNIQUE <replaceable class="parameter">index_parameters</replaceable> |
PRIMARY KEY <replaceable class="parameter">index_parameters</replaceable> |
REFERENCES <replaceable class="parameter">reftable</replaceable> [ ( <replaceable class="parameter">refcolumn</replaceable> ) ] [ MATCH FULL | MATCH PARTIAL | MATCH SIMPLE ]
[ ON DELETE <replaceable class="parameter">referential_action</replaceable> ] [ ON UPDATE <replaceable class="parameter">referential_action</replaceable> ] }
[ DEFERRABLE | NOT DEFERRABLE ] [ INITIALLY DEFERRED | INITIALLY IMMEDIATE ]
<phrase>and <replaceable class="parameter">table_constraint</replaceable> is:</phrase>
[ CONSTRAINT <replaceable class="parameter">constraint_name</replaceable> ]
{ CHECK ( <replaceable class="parameter">expression</replaceable> ) [ NO INHERIT ] |
UNIQUE ( <replaceable class="parameter">column_name</replaceable> [, ... ] ) <replaceable class="parameter">index_parameters</replaceable> |
PRIMARY KEY ( <replaceable class="parameter">column_name</replaceable> [, ... ] ) <replaceable class="parameter">index_parameters</replaceable> |
EXCLUDE [ USING <replaceable class="parameter">index_method</replaceable> ] ( <replaceable class="parameter">exclude_element</replaceable> WITH <replaceable class="parameter">operator</replaceable> [, ... ] ) <replaceable class="parameter">index_parameters</replaceable> [ WHERE ( <replaceable class="parameter">predicate</replaceable> ) ] |
FOREIGN KEY ( <replaceable class="parameter">column_name</replaceable> [, ... ] ) REFERENCES <replaceable class="parameter">reftable</replaceable> [ ( <replaceable class="parameter">refcolumn</replaceable> [, ... ] ) ]
[ MATCH FULL | MATCH PARTIAL | MATCH SIMPLE ] [ ON DELETE <replaceable
class="parameter">referential_action</replaceable> ] [ ON UPDATE <replaceable class="parameter">referential_action</replaceable> ] }
[ DEFERRABLE | NOT DEFERRABLE ] [ INITIALLY DEFERRED | INITIALLY IMMEDIATE ]
<phrase>and <replaceable class="parameter">like_option</replaceable> is:</phrase>
{ INCLUDING | EXCLUDING } { COMMENTS | 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><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><replaceable class="parameter">exclude_element</replaceable> in an <literal>EXCLUDE</literal> constraint is:</phrase>
{ <replaceable class="parameter">column_name</replaceable> | ( <replaceable class="parameter">expression</replaceable> ) } [ <replaceable class="parameter">opclass</replaceable> ] [ ASC | DESC ] [ NULLS { FIRST | LAST } ]
</synopsis>
</refsynopsisdiv>
<refsect1 id="sql-createtable-description">
<title>Description</title>
<para>
<command>CREATE TABLE</command> will create a new, initially empty table
in the current database. The table will be owned by the user issuing the
command.
</para>
<para>
If a schema name is given (for example, <literal>CREATE TABLE
myschema.mytable ...</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 table, sequence, index, view,
or foreign table in the same schema.
</para>
<para>
<command>CREATE TABLE</command> also automatically creates a data
type that represents the composite type corresponding
to one row of the table. Therefore, tables cannot have the same
name as any existing data type in the same schema.
</para>
<para>
The optional constraint clauses specify constraints (tests) that
new or updated rows must satisfy for an insert or update operation
to succeed. A constraint is an SQL object that helps define the
set of valid values in the table in various ways.
</para>
<para>
There are two ways to define constraints: table constraints and
column constraints. A column constraint is defined as part of a
column definition. A table constraint definition is not tied to a
particular column, and it can encompass more than one column.
Every column constraint can also be written as a table constraint;
a column constraint is only a notational convenience for use when the
constraint only affects one column.
</para>
<para>
To be able to create a table, you must have <literal>USAGE</literal>
privilege on all column types or the type in the <literal>OF</literal>
clause, respectively.
</para>
</refsect1>
<refsect1>
<title>Parameters</title>
<variablelist>
<varlistentry 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). Existing permanent
tables with the same name are not visible to the current session
while the temporary table exists, unless they are referenced
with schema-qualified names. Any indexes created on a temporary
table are automatically temporary as well.
</para>
<para>
The <link linkend="autovacuum">autovacuum daemon</link> cannot
access and therefore cannot vacuum or analyze temporary tables.
For this reason, appropriate vacuum and analyze operations should be
performed via session SQL commands. For example, if a temporary
table is going to be used in complex queries, it is wise to run
<command>ANALYZE</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"
endterm="sql-createtable-compatibility-title"/>.
</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>
</listitem>
</varlistentry>
<varlistentry>
<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>
<term><replaceable class="parameter">table_name</replaceable></term>
<listitem>
<para>
The name (optionally schema-qualified) of the table to be created.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>OF <replaceable class="parameter">type_name</replaceable></literal></term>
<listitem>
<para>
Creates a <firstterm>typed table</firstterm>, which takes its
structure from the specified composite type (name optionally
schema-qualified). A typed table is tied to its type; for
example the table will be dropped if the type is dropped
(with <literal>DROP TYPE ... CASCADE</literal>).
</para>
<para>
When a typed table is created, then the data types of the
columns are determined by the underlying composite type and are
not specified by the <literal>CREATE TABLE</literal> command.
But the <literal>CREATE TABLE</literal> command can add defaults
and constraints to the table and can specify storage parameters.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><replaceable class="parameter">column_name</replaceable></term>
<listitem>
<para>
The name of a column to be created in the new table.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><replaceable class="parameter">data_type</replaceable></term>
<listitem>
<para>
The data type of the column. This can include array
specifiers. For more information on the data types supported by
<productname>PostgreSQL</productname>, refer to <xref
linkend="datatype"/>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>COLLATE <replaceable>collation</replaceable></literal></term>
<listitem>
<para>
The <literal>COLLATE</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>
<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>
<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>
Partitioned tables do not support <literal>EXCLUDE</literal> constraints;
however, you can define these constraints on individual partitions.
</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>. This option is not available for
hash-partitioned tables.
</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 a default partition of the parent table. The parent can
either be a list or range partitioned table. A partition key value
not fitting into any other partition of the given parent will be
routed to the default partition. There can be only one default
partition for a given parent table.
</para>
<para>
When a table has an existing <literal>DEFAULT</literal> partition and
a new partition is added to it, the existing 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.
</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 TRUNCATE 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. Note that dropping a partition
with <literal>DROP TABLE</literal> requires taking an <literal>ACCESS
EXCLUSIVE</literal> lock on the parent table.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>LIKE <replaceable>source_table</replaceable> [ <replaceable>like_option</replaceable> ... ]</literal></term>
<listitem>
<para>
The <literal>LIKE</literal> clause specifies a table from which
the new table automatically copies all column names, their data types,
and their not-null constraints.
</para>
<para>
Unlike <literal>INHERITS</literal>, the new table and original table
are completely decoupled after creation is complete. Changes to the
original table will not be applied to the new table, and it is not
possible to include data of the new table in scans of the original
table.
</para>
<para>
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>
<term><literal>INCLUDING COMMENTS</literal></term>
<listitem>
<para>
Comments for the copied columns, constraints, and indexes will be
copied. The default behavior is to exclude comments, resulting in
the copied columns and constraints in the new table having no
comments.
</para>
</listitem>
</varlistentry>
<varlistentry>
<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>
<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>
<term><literal>INCLUDING GENERATED</literal></term>
<listitem>
<para>
Any generation expressions of copied column definitions will be
copied. By default, new columns will be regular base columns.
</para>
</listitem>
</varlistentry>
<varlistentry>
<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>
<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>
<term><literal>INCLUDING STATISTICS</literal></term>
<listitem>
<para>
Extended statistics are copied to the new table.
</para>
</listitem>
</varlistentry>
<varlistentry>
<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>
<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>
<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>
<term><literal>NOT NULL</literal></term>
<listitem>
<para>
The column is not allowed to contain null values.
</para>
</listitem>
</varlistentry>
<varlistentry>
<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>
<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 <literal>tableoid</literal>
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>
<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>
<term><literal>GENERATED ALWAYS AS ( <replaceable>generation_expr</replaceable> ) STORED</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>
The keyword <literal>STORED</literal> is required to signify that the
column will be computed on write and will be stored on disk.
</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>
</listitem>
</varlistentry>
<varlistentry>
<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 the column in new rows will automatically have values from the
sequence assigned to it.
</para>
<para>
The clauses <literal>ALWAYS</literal> and <literal>BY DEFAULT</literal>
determine how the sequence value is given precedence over a
user-specified value in an <command>INSERT</command> statement.
If <literal>ALWAYS</literal> is specified, 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 specified, 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>
The optional <replaceable>sequence_options</replaceable> clause can be
used to override the options of the sequence.
See <xref linkend="sql-createsequence"/> for details.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>UNIQUE</literal> (column constraint)</term>
<term><literal>UNIQUE ( <replaceable class="parameter">column_name</replaceable> [, ... ] )</literal>
<optional> INCLUDE ( <replaceable class="parameter">column_name</replaceable> [, ...]) </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 the unique table constraint
is the same as that for column constraints, with the additional
capability to span multiple columns.
</para>
<para>
For the purpose of a unique constraint, null values are not
considered equal.
</para>
<para>
Each unique table constraint must name a set of columns that is
different from the set of columns named by any other unique or
primary key constraint defined for the table. (Otherwise it
would just be the same constraint listed twice.)
</para>
<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.
The optional clause <literal>INCLUDE</literal> adds to that index
one or more columns on which the uniqueness is not enforced.
Note that although the constraint is not enforced on the included columns,
it still depends on them. Consequently, some operations on these columns
(e.g. <literal>DROP COLUMN</literal>) can cause cascaded constraint and
index deletion.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>PRIMARY KEY</literal> (column constraint)</term>
<term><literal>PRIMARY KEY ( <replaceable class="parameter">column_name</replaceable> [, ... ] )</literal>
<optional> INCLUDE ( <replaceable class="parameter">column_name</replaceable> [, ...]) </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>, but
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>
<literal>PRIMARY KEY</literal> constraints share the restrictions that
<literal>UNIQUE</literal> constraints have when placed on partitioned
tables.
</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. The optional <literal>INCLUDE</literal> clause allows a list
of columns to be specified which will be included in the non-key portion
of the index. Although uniqueness is not enforced on the included columns,
the constraint still depends on them. Consequently, some operations on the
included 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.
</para>
<para>
Exclusion constraints are implemented using
an index, so each specified operator must be associated with an
appropriate operator class
(see <xref linkend="indexes-opclass"/>) for the index access
method <replaceable>index_method</replaceable>.
The operators are required to be commutative.
Each <replaceable class="parameter">exclude_element</replaceable>
can optionally specify an operator class and/or ordering options;
these are described fully under
<xref linkend="sql-createindex"/>.
</para>
<para>
The access method must support <literal>amgettuple</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>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>REFERENCES <replaceable class="parameter">reftable</replaceable> [ ( <replaceable class="parameter">refcolumn</replaceable> ) ] [ MATCH <replaceable class="parameter">matchtype</replaceable> ] [ ON DELETE <replaceable class="parameter">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> [, ... ] )
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>
(table constraint)</term>
<listitem>
<para>
These clauses specify a foreign key constraint, which requires
that a group of one or more columns of the new table must only
contain values that match values in the referenced
column(s) of some row of the referenced table. If the <replaceable
class="parameter">refcolumn</replaceable> list is omitted, the
primary key of the <replaceable class="parameter">reftable</replaceable>
is used. The referenced columns must be the columns of a non-deferrable
unique or primary key constraint in the referenced table. 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 other than the
<literal>NO ACTION</literal> check cannot be deferred, even if
the constraint is declared deferrable. There are the following possible
actions for each clause:
<variablelist>
<varlistentry>
<term><literal>NO ACTION</literal></term>
<listitem>
<para>
Produce an error indicating that the deletion or update
would create a foreign key constraint violation.
If the constraint is deferred, this
error will be produced at constraint check time if there still
exist any referencing rows. This is the default action.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>RESTRICT</literal></term>
<listitem>
<para>
Produce an error indicating that the deletion or update
would create a foreign key constraint violation.
This is the same as <literal>NO ACTION</literal> except that
the check is not deferrable.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>CASCADE</literal></term>
<listitem>
<para>
Delete any rows referencing the deleted row, or update the
values of the referencing column(s) to the new values of the
referenced columns, respectively.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>SET NULL</literal></term>
<listitem>
<para>
Set the referencing column(s) to null.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>SET DEFAULT</literal></term>
<listitem>
<para>
Set the referencing column(s) to their default values.
(There must be a row in the referenced table matching the default
values, if they are not null, or the operation will fail.)
</para>
</listitem>
</varlistentry>
</variablelist>
</para>
<para>
If the referenced column(s) are changed frequently, it might be wise to
add an index to the referencing column(s) so that referential actions
associated with the foreign key constraint can be performed more
efficiently.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>DEFERRABLE</literal></term>
<term><literal>NOT DEFERRABLE</literal></term>
<listitem>
<para>
This controls whether the constraint can be deferred. A
constraint that is not deferrable will be checked immediately
after every command. Checking of constraints that are
deferrable can be postponed until the end of the transaction
(using the <xref linkend="sql-set-constraints"/> command).
<literal>NOT DEFERRABLE</literal> is the default.
Currently, only <literal>UNIQUE</literal>, <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 arbitrators in an <command>INSERT</command> statement that
includes an <literal>ON CONFLICT DO UPDATE</literal> clause.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>INITIALLY IMMEDIATE</literal></term>
<term><literal>INITIALLY DEFERRED</literal></term>
<listitem>
<para>
If a constraint is deferrable, this clause specifies the default
time to check the constraint. If the constraint is
<literal>INITIALLY IMMEDIATE</literal>, it is checked after each
statement. This is the default. If the constraint is
<literal>INITIALLY DEFERRED</literal>, it is checked only at the
end of the transaction. The constraint check time can be
altered with the <xref linkend="sql-set-constraints"/> command.
</para>
</listitem>
</varlistentry>
<varlistentry 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>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>WITH ( <replaceable class="parameter">storage_parameter</replaceable> [= <replaceable class="parameter">value</replaceable>] [, ... ] )</literal></term>
<listitem>
<para>
This clause specifies optional storage parameters for a table or index;
see <xref linkend="sql-createtable-storage-parameters"
endterm="sql-createtable-storage-parameters-title"/> for more
information. 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>
<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>
<term><literal>ON COMMIT</literal></term>
<listitem>
<para>
The behavior of temporary tables at the end of a transaction
block can be controlled using <literal>ON COMMIT</literal>.
The three options are:
<variablelist>
<varlistentry>
<term><literal>PRESERVE ROWS</literal></term>
<listitem>
<para>
No special action is taken at the ends of transactions.
This is the default behavior.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>DELETE ROWS</literal></term>
<listitem>
<para>
All rows in the temporary table will be deleted at the end
of each transaction block. Essentially, an automatic <xref
linkend="sql-truncate"/> is done
at each commit. When used on a partitioned table, this
is not cascaded to its partitions.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>DROP</literal></term>
<listitem>
<para>
The temporary table will be dropped at the end of the current
transaction block. 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>
<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">
<title id="sql-createtable-storage-parameters-title">Storage Parameters</title>
<indexterm zone="sql-createtable-storage-parameters">
<primary>storage parameters</primary>
</indexterm>
<para>
The <literal>WITH</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.
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 move long column values into TOAST tables, and is also the
target length we try to reduce the length below once toasting begins.
This only affects columns marked as either External or Extended
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 blocksize will be 2040 bytes. Valid values are
between 128 bytes and the (blocksize - 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>boolean</type>)
<indexterm>
<primary><varname>vacuum_index_cleanup</varname> storage parameter</primary>
</indexterm>
</term>
<listitem>
<para>
Enables or disables index cleanup when <command>VACUUM</command> is
run on this table. The default value is <literal>true</literal>.
Disabling 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 <xref linkend="sql-vacuum"/>, 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> storage parameter</primary>
</indexterm>
</term>
<listitem>
<para>
Enables or disables vacuum to try to truncate off any empty pages
at the end of this table. The default value is <literal>true</literal>.
If <literal>true</literal>, <command>VACUUM</command> and
autovacuum do the truncation and the disk space for
the truncated pages is returned to the operating system.
Note that the truncation requires <literal>ACCESS EXCLUSIVE</literal>
lock on the table. The <literal>TRUNCATE</literal> parameter
of <xref linkend="sql-vacuum"/>, if specified, overrides the value
of this option.
</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-vauum-scale-factor" xreflabel="autovacuum_vacuum_scale_factor">
<term><literal>autovacuum_vacuum_scale_factor</literal>, <literal>toast.autovacuum_vacuum_scale_factor</literal> (<type>float4</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-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>float4</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-vauum-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-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">
<title id="sql-createtable-compatibility-title">Compatibility</title>
<para>
The <command>CREATE TABLE</command> command conforms to the
<acronym>SQL</acronym> standard, with exceptions listed below.
</para>
<refsect2>
<title>Temporary Tables</title>
<para>
Although the syntax of <literal>CREATE TEMPORARY TABLE</literal>
resembles that of the SQL standard, the effect is not the same. In the
standard,
temporary tables are defined just once and automatically exist (starting
with empty contents) in every session that needs them.
<productname>PostgreSQL</productname> instead
requires each session to issue its own <literal>CREATE TEMPORARY
TABLE</literal> command for each temporary table to be used. This allows
different sessions to use the same temporary table name for different
purposes, whereas the standard's approach constrains all instances of a
given temporary table name to have the same table structure.
</para>
<para>
The standard's definition of the behavior of temporary tables is
widely ignored. <productname>PostgreSQL</productname>'s behavior
on this point is similar to that of several other SQL databases.
</para>
<para>
The SQL standard also distinguishes between global and local temporary
tables, where a local temporary table has a separate set of contents for
each SQL module within each session, though its definition is still shared
across sessions. Since <productname>PostgreSQL</productname> does not
support SQL modules, this distinction is not relevant in
<productname>PostgreSQL</productname>.
</para>
<para>
For compatibility's sake, <productname>PostgreSQL</productname> will
accept the <literal>GLOBAL</literal> and <literal>LOCAL</literal> keywords
in a temporary table declaration, but they currently have no effect.
Use of these keywords is discouraged, since future versions of
<productname>PostgreSQL</productname> might adopt a more
standard-compliant interpretation of their meaning.
</para>
<para>
The <literal>ON COMMIT</literal> clause for temporary tables
also resembles the SQL standard, but has some differences.
If the <literal>ON COMMIT</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><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>
<para>
Currently, <productname>PostgreSQL</productname> does not record names
for <literal>NOT NULL</literal> constraints at all, so they are not
subject to the uniqueness restriction. This might change in a future
release.
</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 option <literal>STORED</literal> is not standard but is 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>. PostgreSQL does not
support these self-referencing columns explicitly, but the same
effect can be had using the OID feature.
</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>
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