Provided by: postgresql-client-17_17.2-1_amd64 
NAME
CREATE_TABLE - define a new table
SYNOPSIS
CREATE [ [ GLOBAL | LOCAL ] { TEMPORARY | TEMP } | UNLOGGED ] TABLE [ IF NOT EXISTS ] table_name ( [
{ column_name data_type [ STORAGE { PLAIN | EXTERNAL | EXTENDED | MAIN | DEFAULT } ] [ COMPRESSION compression_method ] [ COLLATE collation ] [ column_constraint [ ... ] ]
| table_constraint
| LIKE source_table [ like_option ... ] }
[, ... ]
] )
[ INHERITS ( parent_table [, ... ] ) ]
[ PARTITION BY { RANGE | LIST | HASH } ( { column_name | ( expression ) } [ COLLATE collation ] [ opclass ] [, ... ] ) ]
[ USING method ]
[ WITH ( storage_parameter [= value] [, ... ] ) | WITHOUT OIDS ]
[ ON COMMIT { PRESERVE ROWS | DELETE ROWS | DROP } ]
[ TABLESPACE tablespace_name ]
CREATE [ [ GLOBAL | LOCAL ] { TEMPORARY | TEMP } | UNLOGGED ] TABLE [ IF NOT EXISTS ] table_name
OF type_name [ (
{ column_name [ WITH OPTIONS ] [ column_constraint [ ... ] ]
| table_constraint }
[, ... ]
) ]
[ PARTITION BY { RANGE | LIST | HASH } ( { column_name | ( expression ) } [ COLLATE collation ] [ opclass ] [, ... ] ) ]
[ USING method ]
[ WITH ( storage_parameter [= value] [, ... ] ) | WITHOUT OIDS ]
[ ON COMMIT { PRESERVE ROWS | DELETE ROWS | DROP } ]
[ TABLESPACE tablespace_name ]
CREATE [ [ GLOBAL | LOCAL ] { TEMPORARY | TEMP } | UNLOGGED ] TABLE [ IF NOT EXISTS ] table_name
PARTITION OF parent_table [ (
{ column_name [ WITH OPTIONS ] [ column_constraint [ ... ] ]
| table_constraint }
[, ... ]
) ] { FOR VALUES partition_bound_spec | DEFAULT }
[ PARTITION BY { RANGE | LIST | HASH } ( { column_name | ( expression ) } [ COLLATE collation ] [ opclass ] [, ... ] ) ]
[ USING method ]
[ WITH ( storage_parameter [= value] [, ... ] ) | WITHOUT OIDS ]
[ ON COMMIT { PRESERVE ROWS | DELETE ROWS | DROP } ]
[ TABLESPACE tablespace_name ]
where column_constraint is:
[ CONSTRAINT constraint_name ]
{ NOT NULL |
NULL |
CHECK ( expression ) [ NO INHERIT ] |
DEFAULT default_expr |
GENERATED ALWAYS AS ( generation_expr ) STORED |
GENERATED { ALWAYS | BY DEFAULT } AS IDENTITY [ ( sequence_options ) ] |
UNIQUE [ NULLS [ NOT ] DISTINCT ] index_parameters |
PRIMARY KEY index_parameters |
REFERENCES reftable [ ( refcolumn ) ] [ MATCH FULL | MATCH PARTIAL | MATCH SIMPLE ]
[ ON DELETE referential_action ] [ ON UPDATE referential_action ] }
[ DEFERRABLE | NOT DEFERRABLE ] [ INITIALLY DEFERRED | INITIALLY IMMEDIATE ]
and table_constraint is:
[ CONSTRAINT constraint_name ]
{ CHECK ( expression ) [ NO INHERIT ] |
UNIQUE [ NULLS [ NOT ] DISTINCT ] ( column_name [, ... ] ) index_parameters |
PRIMARY KEY ( column_name [, ... ] ) index_parameters |
EXCLUDE [ USING index_method ] ( exclude_element WITH operator [, ... ] ) index_parameters [ WHERE ( predicate ) ] |
FOREIGN KEY ( column_name [, ... ] ) REFERENCES reftable [ ( refcolumn [, ... ] ) ]
[ MATCH FULL | MATCH PARTIAL | MATCH SIMPLE ] [ ON DELETE referential_action ] [ ON UPDATE referential_action ] }
[ DEFERRABLE | NOT DEFERRABLE ] [ INITIALLY DEFERRED | INITIALLY IMMEDIATE ]
and like_option is:
{ INCLUDING | EXCLUDING } { COMMENTS | COMPRESSION | CONSTRAINTS | DEFAULTS | GENERATED | IDENTITY | INDEXES | STATISTICS | STORAGE | ALL }
and partition_bound_spec is:
IN ( partition_bound_expr [, ...] ) |
FROM ( { partition_bound_expr | MINVALUE | MAXVALUE } [, ...] )
TO ( { partition_bound_expr | MINVALUE | MAXVALUE } [, ...] ) |
WITH ( MODULUS numeric_literal, REMAINDER numeric_literal )
index_parameters in UNIQUE, PRIMARY KEY, and EXCLUDE constraints are:
[ INCLUDE ( column_name [, ... ] ) ]
[ WITH ( storage_parameter [= value] [, ... ] ) ]
[ USING INDEX TABLESPACE tablespace_name ]
exclude_element in an EXCLUDE constraint is:
{ column_name | ( expression ) } [ COLLATE collation ] [ opclass [ ( opclass_parameter = value [, ... ] ) ] ] [ ASC | DESC ] [ NULLS { FIRST | LAST } ]
referential_action in a FOREIGN KEY/REFERENCES constraint is:
{ NO ACTION | RESTRICT | CASCADE | SET NULL [ ( column_name [, ... ] ) ] | SET DEFAULT [ ( column_name [, ... ] ) ] }
DESCRIPTION
CREATE TABLE will create a new, initially empty table in the current database. The table
will be owned by the user issuing the command.
If a schema name is given (for example, CREATE TABLE myschema.mytable ...) then the table
is created in the specified schema. Otherwise it is created in the current schema.
Temporary tables exist in a special schema, so a schema name cannot be given when creating
a temporary table. The name of the table must be distinct from the name of any other
relation (table, sequence, index, view, materialized view, or foreign table) in the same
schema.
CREATE TABLE 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.
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.
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.
To be able to create a table, you must have USAGE privilege on all column types or the
type in the OF clause, respectively.
PARAMETERS
TEMPORARY or TEMP
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 ON COMMIT 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.
The autovacuum daemon 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 ANALYZE on the temporary table after it is
populated.
Optionally, GLOBAL or LOCAL can be written before TEMPORARY or TEMP. This presently
makes no difference in PostgreSQL and is deprecated; see Compatibility below.
UNLOGGED
If specified, the table is created as an unlogged table. Data written to unlogged
tables is not written to the write-ahead log (see Chapter 28), 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.
If this is specified, any sequences created together with the unlogged table (for
identity or serial columns) are also created as unlogged.
IF NOT EXISTS
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.
table_name
The name (optionally schema-qualified) of the table to be created.
OF type_name
Creates a typed table, 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 DROP TYPE ... CASCADE).
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 CREATE TABLE command. But
the CREATE TABLE command can add defaults and constraints to the table and can specify
storage parameters.
column_name
The name of a column to be created in the new table.
data_type
The data type of the column. This can include array specifiers. For more information
on the data types supported by PostgreSQL, refer to Chapter 8.
COLLATE collation
The COLLATE clause assigns a collation to the column (which must be of a collatable
data type). If not specified, the column data type's default collation is used.
STORAGE { PLAIN | EXTERNAL | EXTENDED | MAIN | DEFAULT }
This form sets the storage mode for the column. This controls whether this column is
held inline or in a secondary TOAST table, and whether the data should be compressed
or not. PLAIN must be used for fixed-length values such as integer and is inline,
uncompressed. MAIN is for inline, compressible data. EXTERNAL is for external,
uncompressed data, and EXTENDED is for external, compressed data. Writing DEFAULT sets
the storage mode to the default mode for the column's data type. EXTENDED is the
default for most data types that support non-PLAIN storage. Use of EXTERNAL will make
substring operations on very large text and bytea values run faster, at the penalty of
increased storage space. See Section 65.2 for more information.
COMPRESSION compression_method
The COMPRESSION 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 main or extended. (See ALTER TABLE (ALTER_TABLE(7)) 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
pglz and lz4. (lz4 is available only if --with-lz4 was used when building PostgreSQL.)
In addition, compression_method can be default to explicitly specify the default
behavior, which is to consult the default_toast_compression setting at the time of
data insertion to determine the method to use.
INHERITS ( parent_table [, ... ] )
The optional INHERITS clause specifies a list of tables from which the new table
automatically inherits all columns. Parent tables can be plain tables or foreign
tables.
Use of INHERITS creates a persistent relationship between the new child table and its
parent table(s). Schema modifications to the parent(s) normally propagate to children
as well, and by default the data of the child table is included in scans of the
parent(s).
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.
CHECK constraints are merged in essentially the same way as columns: if multiple
parent tables and/or the new table definition contain identically-named CHECK
constraints, these constraints must all have the same check expression, or an error
will be reported. Constraints having the same name and expression will be merged into
one copy. A constraint marked NO INHERIT in a parent will not be considered. Notice
that an unnamed CHECK constraint in the new table will never be merged, since a unique
name will always be chosen for it.
Column STORAGE settings are also copied from parent tables.
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.
PARTITION BY { RANGE | LIST | HASH } ( { column_name | ( expression ) } [ opclass ] [,
...] )
The optional PARTITION BY clause specifies a strategy of partitioning the table. The
table thus created is called a partitioned table. The parenthesized list of columns or
expressions forms the partition key 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 PostgreSQL), but for list partitioning,
the partition key must consist of a single column or expression.
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 Section 36.16.3 for details).
A partitioned table is divided into sub-tables (called partitions), which are created
using separate CREATE TABLE 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.
Partitioned tables do not support EXCLUDE constraints; however, you can define these
constraints on individual partitions.
See Section 5.12 for more discussion on table partitioning.
PARTITION OF parent_table { FOR VALUES partition_bound_spec | DEFAULT }
Creates the table as a partition of the specified parent table. The table can be
created either as a partition for specific values using FOR VALUES or as a default
partition using DEFAULT. Any indexes, constraints and user-defined row-level triggers
that exist in the parent table are cloned on the new partition.
The partition_bound_spec 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 IN is used for list partitioning, the form with FROM and TO is used for
range partitioning, and the form with WITH is used for hash partitioning.
partition_bound_expr 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 CURRENT_TIMESTAMP.
When creating a list partition, NULL 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. NULL cannot be specified for range
partitions.
When creating a range partition, the lower bound specified with FROM is an inclusive
bound, whereas the upper bound specified with TO is an exclusive bound. That is, the
values specified in the FROM list are valid values of the corresponding partition key
columns for this partition, whereas those in the TO list are not. Note that this
statement must be understood according to the rules of row-wise comparison
(Section 9.25.5). For example, given PARTITION BY RANGE (x,y), a partition bound FROM
(1, 2) TO (3, 4) allows x=1 with any y>=2, x=2 with any non-null y, and x=3 with any
y<4.
The special values MINVALUE and MAXVALUE 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 FROM (MINVALUE) TO (10) allows any values less than 10, and
a partition defined using FROM (10) TO (MAXVALUE) allows any values greater than or
equal to 10.
When creating a range partition involving more than one column, it can also make sense
to use MAXVALUE as part of the lower bound, and MINVALUE as part of the upper bound.
For example, a partition defined using FROM (0, MAXVALUE) TO (10, MAXVALUE) 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 FROM ('a', MINVALUE) TO ('b', MINVALUE)
allows any rows where the first partition key column starts with "a".
Note that if MINVALUE or MAXVALUE is used for one column of a partitioning bound, the
same value must be used for all subsequent columns. For example, (10, MINVALUE, 0) is
not a valid bound; you should write (10, MINVALUE, MINVALUE).
Also note that some element types, such as timestamp, have a notion of "infinity",
which is just another value that can be stored. This is different from MINVALUE and
MAXVALUE, which are not real values that can be stored, but rather they are ways of
saying that the value is unbounded. MAXVALUE can be thought of as being greater than
any other value, including "infinity" and MINVALUE as being less than any other value,
including "minus infinity". Thus the range FROM ('infinity') TO (MAXVALUE) is not an
empty range; it allows precisely one value to be stored — "infinity".
If DEFAULT 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.
When a table has an existing DEFAULT 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.
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.
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. CHECK constraints will be inherited
automatically by every partition, but an individual partition may specify additional
CHECK 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.
Rows inserted into a partitioned table will be automatically routed to the correct
partition. If no suitable partition exists, an error will occur.
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 creating a partition using PARTITION OF requires taking an ACCESS EXCLUSIVE
lock on the parent partitioned table. Likewise, dropping a partition with DROP TABLE
requires taking an ACCESS EXCLUSIVE lock on the parent table. It is possible to use
ALTER TABLE ATTACH/DETACH PARTITION to perform these operations with a weaker lock,
thus reducing interference with concurrent operations on the partitioned table.
LIKE source_table [ like_option ... ]
The LIKE clause specifies a table from which the new table automatically copies all
column names, their data types, and their not-null constraints.
Unlike INHERITS, 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.
Also unlike INHERITS, columns and constraints copied by LIKE are not merged with
similarly named columns and constraints. If the same name is specified explicitly or
in another LIKE clause, an error is signaled.
The optional like_option clauses specify which additional properties of the original
table to copy. Specifying INCLUDING copies the property, specifying EXCLUDING omits
the property. EXCLUDING is the default. If multiple specifications are made for the
same kind of object, the last one is used. The available options are:
INCLUDING COMMENTS
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.
INCLUDING COMPRESSION
Compression method of the columns will be copied. The default behavior is to
exclude compression methods, resulting in columns having the default compression
method.
INCLUDING CONSTRAINTS
CHECK constraints will be copied. No distinction is made between column
constraints and table constraints. Not-null constraints are always copied to the
new table.
INCLUDING DEFAULTS
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 nextval, may create a functional linkage
between the original and new tables.
INCLUDING GENERATED
Any generation expressions of copied column definitions will be copied. By
default, new columns will be regular base columns.
INCLUDING IDENTITY
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.
INCLUDING INDEXES
Indexes, PRIMARY KEY, UNIQUE, and EXCLUDE 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.)
INCLUDING STATISTICS
Extended statistics are copied to the new table.
INCLUDING STORAGE
STORAGE settings for the copied column definitions will be copied. The default
behavior is to exclude STORAGE settings, resulting in the copied columns in the
new table having type-specific default settings. For more on STORAGE settings, see
Section 65.2.
INCLUDING ALL
INCLUDING ALL is an abbreviated form selecting all the available individual
options. (It could be useful to write individual EXCLUDING clauses after INCLUDING
ALL to select all but some specific options.)
The LIKE clause can also be used to copy column definitions from views, foreign
tables, or composite types. Inapplicable options (e.g., INCLUDING INDEXES from a view)
are ignored.
CONSTRAINT constraint_name
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 col must be
positive can be used to communicate helpful constraint information to client
applications. (Double-quotes are needed to specify constraint names that contain
spaces.) If a constraint name is not specified, the system generates a name.
NOT NULL
The column is not allowed to contain null values.
NULL
The column is allowed to contain null values. This is the default.
This clause is only provided for compatibility with non-standard SQL databases. Its
use is discouraged in new applications.
CHECK ( expression ) [ NO INHERIT ]
The CHECK clause specifies an expression producing a Boolean result which new or
updated rows must satisfy for an insert or update operation to succeed. Expressions
evaluating to TRUE or UNKNOWN succeed. Should any row of an insert or update operation
produce a FALSE result, an error exception is raised and the insert or update does not
alter the database. A check constraint specified as a column constraint should
reference that column's value only, while an expression appearing in a table
constraint can reference multiple columns.
Currently, CHECK expressions cannot contain subqueries nor refer to variables other
than columns of the current row (see Section 5.5.1). The system column tableoid may be
referenced, but not any other system column.
A constraint marked with NO INHERIT will not propagate to child tables.
When a table has multiple CHECK constraints, they will be tested for each row in
alphabetical order by name, after checking NOT NULL constraints. (PostgreSQL versions
before 9.5 did not honor any particular firing order for CHECK constraints.)
DEFAULT default_expr
The DEFAULT 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.
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.
GENERATED ALWAYS AS ( generation_expr ) STORED
This clause creates the column as a generated column. The column cannot be written to,
and when read the result of the specified expression will be returned.
The keyword STORED is required to signify that the column will be computed on write
and will be stored on disk.
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.
GENERATED { ALWAYS | BY DEFAULT } AS IDENTITY [ ( sequence_options ) ]
This clause creates the column as an identity column. 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 NOT NULL.
The clauses ALWAYS and BY DEFAULT determine how explicitly user-specified values are
handled in INSERT and UPDATE commands.
In an INSERT command, if ALWAYS is selected, a user-specified value is only accepted
if the INSERT statement specifies OVERRIDING SYSTEM VALUE. If BY DEFAULT is selected,
then the user-specified value takes precedence. See INSERT(7) for details. (In the
COPY command, user-specified values are always used regardless of this setting.)
In an UPDATE command, if ALWAYS is selected, any update of the column to any value
other than DEFAULT will be rejected. If BY DEFAULT is selected, the column can be
updated normally. (There is no OVERRIDING clause for the UPDATE command.)
The optional sequence_options clause can be used to override the parameters of the
sequence. The available options include those shown for CREATE SEQUENCE
(CREATE_SEQUENCE(7)), plus SEQUENCE NAME name, LOGGED, and UNLOGGED, which allow
selection of the name and persistence level of the sequence. Without SEQUENCE NAME,
the system chooses an unused name for the sequence. Without LOGGED or UNLOGGED, the
sequence will have the same persistence level as the table.
UNIQUE [ NULLS [ NOT ] DISTINCT ] (column constraint)
UNIQUE [ NULLS [ NOT ] DISTINCT ] ( column_name [, ... ] ) [ INCLUDE ( column_name [,
...]) ] (table constraint)
The UNIQUE 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.
For the purpose of a unique constraint, null values are not considered equal, unless
NULLS NOT DISTINCT is specified.
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.)
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.
Adding a unique constraint will automatically create a unique btree index on the
column or group of columns used in the constraint. The created index has the same name
as the unique constraint.
The optional INCLUDE clause adds to that index one or more columns that are simply
“payload”: 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., DROP COLUMN) can cause cascaded
constraint and index deletion.
PRIMARY KEY (column constraint)
PRIMARY KEY ( column_name [, ... ] ) [ INCLUDE ( column_name [, ...]) ] (table constraint)
The PRIMARY KEY 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.
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.)
PRIMARY KEY enforces the same data constraints as a combination of UNIQUE and NOT
NULL. 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.
When placed on a partitioned table, PRIMARY KEY constraints share the restrictions
previously described for UNIQUE constraints.
Adding a PRIMARY KEY constraint will automatically create a unique btree index on the
column or group of columns used in the constraint. That index has the same name as the
primary key constraint.
The optional INCLUDE clause adds to that index one or more columns that are simply
“payload”: 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., DROP COLUMN) can cause cascaded
constraint and index deletion.
EXCLUDE [ USING index_method ] ( exclude_element WITH operator [, ... ] ) index_parameters
[ WHERE ( predicate ) ]
The EXCLUDE clause defines an exclusion constraint, which guarantees that if any two
rows are compared on the specified column(s) or expression(s) using the specified
operator(s), not all of these comparisons will return TRUE. If all of the specified
operators test for equality, this is equivalent to a UNIQUE constraint, although an
ordinary unique constraint will be faster. However, exclusion constraints can specify
constraints that are more general than simple equality. For example, you can specify a
constraint that no two rows in the table contain overlapping circles (see Section 8.8)
by using the && operator. The operator(s) are required to be commutative.
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 Section 11.10) for the index access method index_method. Each
exclude_element 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 CREATE INDEX (CREATE_INDEX(7)).
The access method must support amgettuple (see Chapter 62); at present this means GIN
cannot be used. Although it's allowed, there is little point in using B-tree or hash
indexes with an exclusion constraint, because this does nothing that an ordinary
unique constraint doesn't do better. So in practice the access method will always be
GiST or SP-GiST.
The predicate allows you to specify an exclusion constraint on a subset of the table;
internally this creates a partial index. Note that parentheses are required around the
predicate.
REFERENCES reftable [ ( refcolumn ) ] [ MATCH matchtype ] [ ON DELETE referential_action ]
[ ON UPDATE referential_action ] (column constraint)
FOREIGN KEY ( column_name [, ... ] ) REFERENCES reftable [ ( refcolumn [, ... ] ) ] [
MATCH matchtype ] [ ON DELETE referential_action ] [ ON UPDATE referential_action ] (table
constraint)
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 refcolumn list is
omitted, the primary key of the reftable is used. Otherwise, the refcolumn 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. The user must have REFERENCES permission on the
referenced table (either the whole table, or the specific referenced columns). The
addition of a foreign key constraint requires a SHARE ROW EXCLUSIVE lock on the
referenced table. Note that foreign key constraints cannot be defined between
temporary tables and permanent tables.
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: MATCH FULL, MATCH PARTIAL, and MATCH SIMPLE (which is the default).
MATCH FULL will not allow one column of a multicolumn foreign key to be null unless
all foreign key columns are null; if they are all null, the row is not required to
have a match in the referenced table. MATCH SIMPLE 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. MATCH PARTIAL is not yet implemented. (Of course, NOT NULL
constraints can be applied to the referencing column(s) to prevent these cases from
arising.)
In addition, when the data in the referenced columns is changed, certain actions are
performed on the data in this table's columns. The ON DELETE clause specifies the
action to perform when a referenced row in the referenced table is being deleted.
Likewise, the ON UPDATE 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 NO ACTION check cannot be deferred, even if the constraint is
declared deferrable. There are the following possible actions for each clause:
NO ACTION
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.
RESTRICT
Produce an error indicating that the deletion or update would create a foreign key
constraint violation. This is the same as NO ACTION except that the check is not
deferrable.
CASCADE
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.
SET NULL [ ( column_name [, ... ] ) ]
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 ON DELETE actions.
SET DEFAULT [ ( column_name [, ... ] ) ]
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 ON
DELETE actions. (There must be a row in the referenced table matching the default
values, if they are not null, or the operation will fail.)
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.
DEFERRABLE
NOT DEFERRABLE
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 SET
CONSTRAINTS command). NOT DEFERRABLE is the default. Currently, only UNIQUE, PRIMARY
KEY, EXCLUDE, and REFERENCES (foreign key) constraints accept this clause. NOT NULL
and CHECK constraints are not deferrable. Note that deferrable constraints cannot be
used as conflict arbitrators in an INSERT statement that includes an ON CONFLICT DO
UPDATE clause.
INITIALLY IMMEDIATE
INITIALLY DEFERRED
If a constraint is deferrable, this clause specifies the default time to check the
constraint. If the constraint is INITIALLY IMMEDIATE, it is checked after each
statement. This is the default. If the constraint is INITIALLY DEFERRED, it is checked
only at the end of the transaction. The constraint check time can be altered with the
SET CONSTRAINTS command.
USING method
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 TABLE. See Chapter 61
for more information. If this option is not specified, the default table access method
is chosen for the new table. See default_table_access_method for more information.
When creating a partition, the table access method is the access method of its
partitioned table, if set.
WITH ( storage_parameter [= value] [, ... ] )
This clause specifies optional storage parameters for a table or index; see Storage
Parameters below for more information. For backward-compatibility the WITH clause for
a table can also include OIDS=FALSE to specify that rows of the new table should not
contain OIDs (object identifiers), OIDS=TRUE is not supported anymore.
WITHOUT OIDS
This is backward-compatible syntax for declaring a table WITHOUT OIDS, creating a
table WITH OIDS is not supported anymore.
ON COMMIT
The behavior of temporary tables at the end of a transaction block can be controlled
using ON COMMIT. The three options are:
PRESERVE ROWS
No special action is taken at the ends of transactions. This is the default
behavior.
DELETE ROWS
All rows in the temporary table will be deleted at the end of each transaction
block. Essentially, an automatic TRUNCATE is done at each commit. When used on a
partitioned table, this is not cascaded to its partitions.
DROP
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.
TABLESPACE tablespace_name
The tablespace_name is the name of the tablespace in which the new table is to be
created. If not specified, default_tablespace is consulted, or temp_tablespaces if the
table is temporary. For partitioned tables, since no storage is required for the table
itself, the tablespace specified overrides default_tablespace as the default
tablespace to use for any newly created partitions when no other tablespace is
explicitly specified.
USING INDEX TABLESPACE tablespace_name
This clause allows selection of the tablespace in which the index associated with a
UNIQUE, PRIMARY KEY, or EXCLUDE constraint will be created. If not specified,
default_tablespace is consulted, or temp_tablespaces if the table is temporary.
Storage Parameters
The WITH clause can specify storage parameters for tables, and for indexes associated with
a UNIQUE, PRIMARY KEY, or EXCLUDE constraint. Storage parameters for indexes are
documented in CREATE INDEX (CREATE_INDEX(7)). 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 toast., which controls the behavior
of the table's secondary TOAST table, if any (see Section 65.2 for more information about
TOAST). If a table parameter value is set and the equivalent toast. 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.
fillfactor (integer)
The fillfactor for a table is a percentage between 10 and 100. 100 (complete packing)
is the default. When a smaller fillfactor is specified, INSERT operations pack table
pages only to the indicated percentage; the remaining space on each page is reserved
for updating rows on that page. This gives UPDATE a chance to place the updated copy
of a row on the same page as the original, which is more efficient than placing it on
a different page, and makes heap-only tuple updates 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.
toast_tuple_target (integer)
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.
parallel_workers (integer)
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 max_worker_processes.
autovacuum_enabled, toast.autovacuum_enabled (boolean)
Enables or disables the autovacuum daemon for a particular table. If true, the
autovacuum daemon will perform automatic VACUUM and/or ANALYZE operations on this
table following the rules discussed in Section 24.1.6. If false, this table will not
be autovacuumed, except to prevent transaction ID wraparound. See Section 24.1.5 for
more about wraparound prevention. Note that the autovacuum daemon does not run at all
(except to prevent transaction ID wraparound) if the 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 true, only to
false.
vacuum_index_cleanup, toast.vacuum_index_cleanup (enum)
Forces or disables index cleanup when VACUUM is run on this table. The default value
is AUTO. With OFF, index cleanup is disabled, with ON it is enabled, and with AUTO a
decision is made dynamically, each time VACUUM runs. The dynamic behavior allows
VACUUM to avoid needlessly scanning indexes to remove very few dead tuples. Forcibly
disabling all index cleanup can speed up VACUUM very significantly, but may also lead
to severely bloated indexes if table modifications are frequent. The INDEX_CLEANUP
parameter of VACUUM, if specified, overrides the value of this option.
vacuum_truncate, toast.vacuum_truncate (boolean)
Enables or disables vacuum to try to truncate off any empty pages at the end of this
table. The default value is true. If true, VACUUM and autovacuum do the truncation and
the disk space for the truncated pages is returned to the operating system. Note that
the truncation requires ACCESS EXCLUSIVE lock on the table. The TRUNCATE parameter of
VACUUM, if specified, overrides the value of this option.
autovacuum_vacuum_threshold, toast.autovacuum_vacuum_threshold (integer)
Per-table value for autovacuum_vacuum_threshold parameter.
autovacuum_vacuum_scale_factor, toast.autovacuum_vacuum_scale_factor (floating point)
Per-table value for autovacuum_vacuum_scale_factor parameter.
autovacuum_vacuum_insert_threshold, toast.autovacuum_vacuum_insert_threshold (integer)
Per-table value for autovacuum_vacuum_insert_threshold parameter. The special value of
-1 may be used to disable insert vacuums on the table.
autovacuum_vacuum_insert_scale_factor, toast.autovacuum_vacuum_insert_scale_factor
(floating point)
Per-table value for autovacuum_vacuum_insert_scale_factor parameter.
autovacuum_analyze_threshold (integer)
Per-table value for autovacuum_analyze_threshold parameter.
autovacuum_analyze_scale_factor (floating point)
Per-table value for autovacuum_analyze_scale_factor parameter.
autovacuum_vacuum_cost_delay, toast.autovacuum_vacuum_cost_delay (floating point)
Per-table value for autovacuum_vacuum_cost_delay parameter.
autovacuum_vacuum_cost_limit, toast.autovacuum_vacuum_cost_limit (integer)
Per-table value for autovacuum_vacuum_cost_limit parameter.
autovacuum_freeze_min_age, toast.autovacuum_freeze_min_age (integer)
Per-table value for vacuum_freeze_min_age parameter. Note that autovacuum will ignore
per-table autovacuum_freeze_min_age parameters that are larger than half the
system-wide autovacuum_freeze_max_age setting.
autovacuum_freeze_max_age, toast.autovacuum_freeze_max_age (integer)
Per-table value for autovacuum_freeze_max_age parameter. Note that autovacuum will
ignore per-table autovacuum_freeze_max_age parameters that are larger than the
system-wide setting (it can only be set smaller).
autovacuum_freeze_table_age, toast.autovacuum_freeze_table_age (integer)
Per-table value for vacuum_freeze_table_age parameter.
autovacuum_multixact_freeze_min_age, toast.autovacuum_multixact_freeze_min_age (integer)
Per-table value for vacuum_multixact_freeze_min_age parameter. Note that autovacuum
will ignore per-table autovacuum_multixact_freeze_min_age parameters that are larger
than half the system-wide autovacuum_multixact_freeze_max_age setting.
autovacuum_multixact_freeze_max_age, toast.autovacuum_multixact_freeze_max_age (integer)
Per-table value for autovacuum_multixact_freeze_max_age parameter. Note that
autovacuum will ignore per-table autovacuum_multixact_freeze_max_age parameters that
are larger than the system-wide setting (it can only be set smaller).
autovacuum_multixact_freeze_table_age, toast.autovacuum_multixact_freeze_table_age
(integer)
Per-table value for vacuum_multixact_freeze_table_age parameter.
log_autovacuum_min_duration, toast.log_autovacuum_min_duration (integer)
Per-table value for log_autovacuum_min_duration parameter.
user_catalog_table (boolean)
Declare the table as an additional catalog table for purposes of logical replication.
See Section 47.6.2 for details. This parameter cannot be set for TOAST tables.
NOTES
PostgreSQL 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 CREATE INDEX (CREATE_INDEX(7)) for more information.)
Unique constraints and primary keys are not inherited in the current implementation. This
makes the combination of inheritance and unique constraints rather dysfunctional.
A table cannot have more than 1600 columns. (In practice, the effective limit is usually
lower because of tuple-length constraints.)
EXAMPLES
Create table films and table distributors:
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 <> '')
);
Create a table with a 2-dimensional array:
CREATE TABLE array_int (
vector int[][]
);
Define a unique table constraint for the table films. Unique table constraints can be
defined on one or more columns of the table:
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)
);
Define a check column constraint:
CREATE TABLE distributors (
did integer CHECK (did > 100),
name varchar(40)
);
Define a check table constraint:
CREATE TABLE distributors (
did integer,
name varchar(40),
CONSTRAINT con1 CHECK (did > 100 AND name <> '')
);
Define a primary key table constraint for the table films:
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)
);
Define a primary key constraint for table distributors. The following two examples are
equivalent, the first using the table constraint syntax, the second the column constraint
syntax:
CREATE TABLE distributors (
did integer,
name varchar(40),
PRIMARY KEY(did)
);
CREATE TABLE distributors (
did integer PRIMARY KEY,
name varchar(40)
);
Assign a literal constant default value for the column name, arrange for the default value
of column did to be generated by selecting the next value of a sequence object, and make
the default value of modtime be the time at which the row is inserted:
CREATE TABLE distributors (
name varchar(40) DEFAULT 'Luso Films',
did integer DEFAULT nextval('distributors_serial'),
modtime timestamp DEFAULT current_timestamp
);
Define two NOT NULL column constraints on the table distributors, one of which is
explicitly given a name:
CREATE TABLE distributors (
did integer CONSTRAINT no_null NOT NULL,
name varchar(40) NOT NULL
);
Define a unique constraint for the name column:
CREATE TABLE distributors (
did integer,
name varchar(40) UNIQUE
);
The same, specified as a table constraint:
CREATE TABLE distributors (
did integer,
name varchar(40),
UNIQUE(name)
);
Create the same table, specifying 70% fill factor for both the table and its unique index:
CREATE TABLE distributors (
did integer,
name varchar(40),
UNIQUE(name) WITH (fillfactor=70)
)
WITH (fillfactor=70);
Create table circles with an exclusion constraint that prevents any two circles from
overlapping:
CREATE TABLE circles (
c circle,
EXCLUDE USING gist (c WITH &&)
);
Create table cinemas in tablespace diskvol1:
CREATE TABLE cinemas (
id serial,
name text,
location text
) TABLESPACE diskvol1;
Create a composite type and a typed table:
CREATE TYPE employee_type AS (name text, salary numeric);
CREATE TABLE employees OF employee_type (
PRIMARY KEY (name),
salary WITH OPTIONS DEFAULT 1000
);
Create a range partitioned table:
CREATE TABLE measurement (
logdate date not null,
peaktemp int,
unitsales int
) PARTITION BY RANGE (logdate);
Create a range partitioned table with multiple columns in the partition key:
CREATE TABLE measurement_year_month (
logdate date not null,
peaktemp int,
unitsales int
) PARTITION BY RANGE (EXTRACT(YEAR FROM logdate), EXTRACT(MONTH FROM logdate));
Create a list partitioned table:
CREATE TABLE cities (
city_id bigserial not null,
name text not null,
population bigint
) PARTITION BY LIST (left(lower(name), 1));
Create a hash partitioned table:
CREATE TABLE orders (
order_id bigint not null,
cust_id bigint not null,
status text
) PARTITION BY HASH (order_id);
Create partition of a range partitioned table:
CREATE TABLE measurement_y2016m07
PARTITION OF measurement (
unitsales DEFAULT 0
) FOR VALUES FROM ('2016-07-01') TO ('2016-08-01');
Create a few partitions of a range partitioned table with multiple columns in the
partition key:
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);
Create partition of a list partitioned table:
CREATE TABLE cities_ab
PARTITION OF cities (
CONSTRAINT city_id_nonzero CHECK (city_id != 0)
) FOR VALUES IN ('a', 'b');
Create partition of a list partitioned table that is itself further partitioned and then
add a partition to it:
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);
Create partitions of a hash partitioned table:
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);
Create a default partition:
CREATE TABLE cities_partdef
PARTITION OF cities DEFAULT;
COMPATIBILITY
The CREATE TABLE command conforms to the SQL standard, with exceptions listed below.
Temporary Tables
Although the syntax of CREATE TEMPORARY TABLE 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.
PostgreSQL instead requires each session to issue its own CREATE TEMPORARY TABLE 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.
The standard's definition of the behavior of temporary tables is widely ignored.
PostgreSQL's behavior on this point is similar to that of several other SQL databases.
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 PostgreSQL does not
support SQL modules, this distinction is not relevant in PostgreSQL.
For compatibility's sake, PostgreSQL will accept the GLOBAL and LOCAL keywords in a
temporary table declaration, but they currently have no effect. Use of these keywords is
discouraged, since future versions of PostgreSQL might adopt a more standard-compliant
interpretation of their meaning.
The ON COMMIT clause for temporary tables also resembles the SQL standard, but has some
differences. If the ON COMMIT clause is omitted, SQL specifies that the default behavior
is ON COMMIT DELETE ROWS. However, the default behavior in PostgreSQL is ON COMMIT
PRESERVE ROWS. The ON COMMIT DROP option does not exist in SQL.
Non-Deferred Uniqueness Constraints
When a UNIQUE or PRIMARY KEY constraint is not deferrable, PostgreSQL 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 DEFERRABLE but not deferred (i.e.,
INITIALLY IMMEDIATE). Be aware that this can be significantly slower than immediate
uniqueness checking.
Column Check Constraints
The SQL standard says that CHECK column constraints can only refer to the column they
apply to; only CHECK table constraints can refer to multiple columns. PostgreSQL does not
enforce this restriction; it treats column and table check constraints alike.
EXCLUDE Constraint
The EXCLUDE constraint type is a PostgreSQL extension.
Foreign Key Constraints
The ability to specify column lists in the foreign key actions SET DEFAULT and SET NULL is
a PostgreSQL extension.
It is a PostgreSQL extension that a foreign key constraint may reference columns of a
unique index instead of columns of a primary key or unique constraint.
NULL “Constraint”
The NULL “constraint” (actually a non-constraint) is a PostgreSQL extension to the SQL
standard that is included for compatibility with some other database systems (and for
symmetry with the NOT NULL constraint). Since it is the default for any column, its
presence is simply noise.
Constraint Naming
The SQL standard says that table and domain constraints must have names that are unique
across the schema containing the table or domain. PostgreSQL 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 (UNIQUE,
PRIMARY KEY, and EXCLUDE 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.
Currently, PostgreSQL does not record names for not-null constraints at all, so they are
not subject to the uniqueness restriction. This might change in a future release.
Inheritance
Multiple inheritance via the INHERITS clause is a PostgreSQL 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 PostgreSQL.
Zero-Column Tables
PostgreSQL allows a table of no columns to be created (for example, CREATE TABLE foo();).
This is an extension from the SQL standard, which does not allow zero-column tables.
Zero-column tables are not in themselves very useful, but disallowing them creates odd
special cases for ALTER TABLE DROP COLUMN, so it seems cleaner to ignore this spec
restriction.
Multiple Identity Columns
PostgreSQL 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 INSERT command supports
only one override clause that applies to the entire statement, so having multiple identity
columns with different behaviors is not well supported.
Generated Columns
The option STORED is not standard but is also used by other SQL implementations. The SQL
standard does not specify the storage of generated columns.
LIKE Clause
While a LIKE clause exists in the SQL standard, many of the options that PostgreSQL
accepts for it are not in the standard, and some of the standard's options are not
implemented by PostgreSQL.
WITH Clause
The WITH clause is a PostgreSQL extension; storage parameters are not in the standard.
Tablespaces
The PostgreSQL concept of tablespaces is not part of the standard. Hence, the clauses
TABLESPACE and USING INDEX TABLESPACE are extensions.
Typed Tables
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 “self-referencing column”. PostgreSQL does not support
self-referencing columns explicitly.
PARTITION BY Clause
The PARTITION BY clause is a PostgreSQL extension.
PARTITION OF Clause
The PARTITION OF clause is a PostgreSQL extension.
SEE ALSO
ALTER TABLE (ALTER_TABLE(7)), DROP TABLE (DROP_TABLE(7)), CREATE TABLE AS
(CREATE_TABLE_AS(7)), CREATE TABLESPACE (CREATE_TABLESPACE(7)), CREATE TYPE
(CREATE_TYPE(7))