CREATE TABLE(7) PostgreSQL 15.10 Documentation CREATE TABLE(7)
NAME
CREATE_TABLE - define a new table
SYNOPSIS
CREATE [ [ GLOBAL | LOCAL ] { TEMPORARY | TEMP } | UNLOGGED ] TABLE [ IF NOT EXISTS ] table_name ( [
{ column_name data_type [ 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 30), 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.
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 38.16.3 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 5.11 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 9.24.5). 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 73.2.
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 5.4.1). 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 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.
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, 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 64); 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 63 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.
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 73.2 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 25.1.6. If false, this table will not be autovacuumed,
except to prevent transaction ID wraparound. See Section 25.1.5 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 49.6.2 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))
PostgreSQL 15.10 2024 CREATE TABLE(7)
postgresql 15.10 - Generated Thu Dec 12 11:13:08 CST 2024