CREATE TABLE — define a new table
CREATE [ [ GLOBAL | LOCAL ] { TEMPORARY | TEMP } | UNLOGGED ] TABLE [ IF NOT EXISTS ]table_name
( [ {column_name
data_type
[ COLLATEcollation
] [column_constraint
[ ... ] ] |table_constraint
| LIKEsource_table
[like_option
... ] } [, ... ] ] ) [ INHERITS (parent_table
[, ... ] ) ] [ WITH (storage_parameter
[=value
] [, ... ] ) | WITH OIDS | WITHOUT OIDS ] [ ON COMMIT { PRESERVE ROWS | DELETE ROWS | DROP } ] [ TABLESPACEtablespace_name
] CREATE [ [ GLOBAL | LOCAL ] { TEMPORARY | TEMP } | UNLOGGED ] TABLE [ IF NOT EXISTS ]table_name
OFtype_name
[ ( {column_name
WITH OPTIONS [column_constraint
[ ... ] ] |table_constraint
} [, ... ] ) ] [ WITH (storage_parameter
[=value
] [, ... ] ) | WITH OIDS | WITHOUT OIDS ] [ ON COMMIT { PRESERVE ROWS | DELETE ROWS | DROP } ] [ TABLESPACEtablespace_name
] wherecolumn_constraint
is: [ CONSTRAINTconstraint_name
] { NOT NULL | NULL | CHECK (expression
) [ NO INHERIT ] | DEFAULTdefault_expr
| UNIQUEindex_parameters
| PRIMARY KEYindex_parameters
| REFERENCESreftable
[ (refcolumn
) ] [ MATCH FULL | MATCH PARTIAL | MATCH SIMPLE ] [ ON DELETEaction
] [ ON UPDATEaction
] } [ DEFERRABLE | NOT DEFERRABLE ] [ INITIALLY DEFERRED | INITIALLY IMMEDIATE ] andtable_constraint
is: [ CONSTRAINTconstraint_name
] { CHECK (expression
) [ NO INHERIT ] | UNIQUE (column_name
[, ... ] )index_parameters
| PRIMARY KEY (column_name
[, ... ] )index_parameters
| EXCLUDE [ USINGindex_method
] (exclude_element
WITHoperator
[, ... ] )index_parameters
[ WHERE (predicate
) ] | FOREIGN KEY (column_name
[, ... ] ) REFERENCESreftable
[ (refcolumn
[, ... ] ) ] [ MATCH FULL | MATCH PARTIAL | MATCH SIMPLE ] [ ON DELETEaction
] [ ON UPDATEaction
] } [ DEFERRABLE | NOT DEFERRABLE ] [ INITIALLY DEFERRED | INITIALLY IMMEDIATE ] andlike_option
is: { INCLUDING | EXCLUDING } { DEFAULTS | CONSTRAINTS | INDEXES | STORAGE | COMMENTS | ALL }index_parameters
inUNIQUE
,PRIMARY KEY
, andEXCLUDE
constraints are: [ WITH (storage_parameter
[=value
] [, ... ] ) ] [ USING INDEX TABLESPACEtablespace_name
]exclude_element
in anEXCLUDE
constraint is: {column_name
| (expression
) } [opclass
] [ ASC | DESC ] [ NULLS { FIRST | LAST } ]
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 table, sequence, index, 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.
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). Existing permanent
tables with the same name are not visible to the current session
while the temporary table exists, unless they are referenced
with schema-qualified names. Any indexes created on a temporary
table are automatically temporary as well.
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.
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 29, Reliability and the Write-Ahead Log), 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 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, Data Types.
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.
INHERITS ( parent_table
[, ... ] )
The optional INHERITS
clause specifies a list of
tables from which the new table automatically inherits all
columns.
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.
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.
Default expressions for the copied column definitions will only be
copied if INCLUDING DEFAULTS
is specified.
Defaults that call database-modification functions, like
nextval
, create a linkage between the original and
new tables. The
default behavior is to exclude default expressions, resulting in the
copied columns in the new table having null defaults.
Not-null constraints are always copied to the new table.
CHECK
constraints will be copied only if
INCLUDING CONSTRAINTS
is specified.
Indexes, PRIMARY KEY
, and UNIQUE
constraints
on the original table will be created on the new table only if the
INCLUDING INDEXES
clause is specified.
No distinction is made between column constraints and table
constraints.
STORAGE
settings for the copied column definitions will only
be copied if INCLUDING STORAGE
is specified. 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
the section called “TOAST”.
Comments for the copied columns, constraints, and indexes
will only be copied if INCLUDING COMMENTS
is specified. The default behavior is to exclude comments, resulting in
the copied columns and constraints in the new table having no comments.
INCLUDING ALL
is an abbreviated form of
INCLUDING DEFAULTS INCLUDING CONSTRAINTS INCLUDING INDEXES INCLUDING STORAGE INCLUDING COMMENTS
.
Note also that 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 LIKE
clause can also be used to copy columns 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. 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.
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 (subqueries and cross-references
to other columns in the current table are not allowed). The
data type of the default expression must match the data type of the
column.
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.
UNIQUE
(column constraint), UNIQUE ( 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 the unique table constraint
is the same as that for column constraints, with the additional
capability to span multiple columns.
For the purpose of a unique constraint, null values are not considered equal.
Each unique table constraint must name a set of columns that is different from the set of columns named by any other unique or primary key constraint defined for the table. (Otherwise it would just be the same constraint listed twice.)
PRIMARY KEY
(column constraint), PRIMARY KEY ( 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.
Technically, PRIMARY KEY
is merely a
combination of UNIQUE
and NOT NULL
, but
identifying a set of columns as primary key also provides
metadata about the design of the schema, as a primary key
implies that other tables
can rely on this set of columns as a unique identifier for rows.
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 other sets of columns named by any unique constraint defined for the same table.
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 the section called “Geometric Types”) by using the
&&
operator.
Exclusion constraints are implemented using
an index, so each specified operator must be associated with an
appropriate operator class
(see the section called “Operator Classes and Operator Families”) for the index access
method index_method
.
The operators are required to be commutative.
Each exclude_element
can optionally specify an operator class and/or ordering options;
these are described fully under
CREATE INDEX(7).
The access method must support amgettuple
(see Chapter 55, Index Access Method Interface Definition); 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 action
] [ ON UPDATE action
]
(column constraint), FOREIGN KEY ( column_name
[, ... ] )
REFERENCES reftable
[ ( refcolumn
[, ... ] ) ]
[ MATCH matchtype
]
[ ON DELETE action
]
[ ON UPDATE 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. The referenced columns must be the columns of a non-deferrable
unique or primary key constraint in the referenced table. Note that
foreign key constraints cannot be defined between temporary tables and
permanent tables.
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
Set the referencing column(s) to null.
SET DEFAULT
Set the referencing column(s) to their default values. (There must be a row in the referenced table matching the default values, if they are not null, or the operation will fail.)
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(7) 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.
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(7) command.
WITH ( storage_parameter
[= value
] [, ... ] )
This clause specifies optional storage parameters for a table or index;
see Storage Parameters for more
information. The WITH
clause for a
table can also include OIDS=TRUE
(or just OIDS
)
to specify that rows of the new table
should have OIDs (object identifiers) assigned to them, or
OIDS=FALSE
to specify that the rows should not have OIDs.
If OIDS
is not specified, the default setting depends upon
the default_with_oids configuration parameter.
(If the new table inherits from any tables that have OIDs, then
OIDS=TRUE
is forced even if the command says
OIDS=FALSE
.)
If OIDS=FALSE
is specified or implied, the new
table does not store OIDs and no OID will be assigned for a row inserted
into it. This is generally considered worthwhile, since it
will reduce OID consumption and thereby postpone the wraparound
of the 32-bit OID counter. Once the counter wraps around, OIDs
can no longer be assumed to be unique, which makes them
considerably less useful. In addition, excluding OIDs from a
table reduces the space required to store the table on disk by
4 bytes per row (on most machines), slightly improving performance.
To remove OIDs from a table after it has been created, use ALTER TABLE(7).
WITH OIDS
, WITHOUT OIDS
These are obsolescent syntaxes equivalent to WITH (OIDS)
and WITH (OIDS=FALSE)
, respectively. If you wish to give
both an OIDS
setting and storage parameters, you must use
the WITH ( ... )
syntax; see above.
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(7) is done at each commit.
DROP
The temporary table will be dropped at the end of the current transaction block.
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.
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.
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(7).
The storage parameters currently
available for tables are listed below. For each parameter, unless noted,
there is an additional parameter with the same name prefixed with
toast.
, which can be used to control the behavior of the
table's secondary TOAST table, if any
(see the section called “TOAST” for more information about TOAST).
Note that the TOAST table inherits the
autovacuum_*
values from its parent table, if there are
no toast.autovacuum_*
settings set.
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. 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.
autovacuum_enabled
, toast.autovacuum_enabled
(boolean) Enables or disables the autovacuum daemon on a particular table.
If true, the autovacuum daemon will initiate a VACUUM operation
on a particular table when the number of updated or deleted tuples exceeds
autovacuum_vacuum_threshold
plus
autovacuum_vacuum_scale_factor
times the number of live tuples
currently estimated to be in the relation.
Similarly, it will initiate an ANALYZE operation when the
number of inserted, updated or deleted tuples exceeds
autovacuum_analyze_threshold
plus
autovacuum_analyze_scale_factor
times the number of live tuples
currently estimated to be in the relation.
If false, this table will not be autovacuumed, except to prevent
transaction Id wraparound. See the section called “Preventing Transaction ID Wraparound Failures” for
more about wraparound prevention.
Observe that this variable inherits its value from the autovacuum setting.
autovacuum_vacuum_threshold
, toast.autovacuum_vacuum_threshold
(integer)Minimum number of updated or deleted tuples before initiate a VACUUM operation on a particular table.
autovacuum_vacuum_scale_factor
, toast.autovacuum_vacuum_scale_factor
(float4) Multiplier for reltuples
to add to
autovacuum_vacuum_threshold
.
autovacuum_analyze_threshold
(integer)Minimum number of inserted, updated, or deleted tuples before initiate an ANALYZE operation on a particular table.
autovacuum_analyze_scale_factor
(float4) Multiplier for reltuples
to add to
autovacuum_analyze_threshold
.
autovacuum_vacuum_cost_delay
, toast.autovacuum_vacuum_cost_delay
(integer)Custom autovacuum_vacuum_cost_delay parameter.
autovacuum_vacuum_cost_limit
, toast.autovacuum_vacuum_cost_limit
(integer)Custom autovacuum_vacuum_cost_limit parameter.
autovacuum_freeze_min_age
, toast.autovacuum_freeze_min_age
(integer) Custom vacuum_freeze_min_age parameter. Note that
autovacuum will ignore attempts to set a per-table
autovacuum_freeze_min_age
larger than half the system-wide
autovacuum_freeze_max_age setting.
autovacuum_freeze_max_age
, toast.autovacuum_freeze_max_age
(integer) Custom autovacuum_freeze_max_age parameter. Note that
autovacuum will ignore attempts to set a per-table
autovacuum_freeze_max_age
larger than the system-wide setting
(it can only be set smaller). Note that while you can set
autovacuum_freeze_max_age
very small, or even zero, this is
usually unwise since it will force frequent vacuuming.
autovacuum_freeze_table_age
, toast.autovacuum_freeze_table_age
(integer)Custom vacuum_freeze_table_age parameter.
autovacuum_multixact_freeze_min_age
, toast.autovacuum_multixact_freeze_min_age
(integer) Custom vacuum_multixact_freeze_min_age parameter.
Note that autovacuum will ignore attempts to set a per-table
autovacuum_multixact_freeze_min_age
larger than half the
system-wide autovacuum_multixact_freeze_max_age
setting.
autovacuum_multixact_freeze_max_age
, toast.autovacuum_multixact_freeze_max_age
(integer) Custom autovacuum_multixact_freeze_max_age parameter. Note
that autovacuum will ignore attempts to set a per-table
autovacuum_multixact_freeze_max_age
larger than the
system-wide setting (it can only be set smaller). Note that while you
can set autovacuum_multixact_freeze_max_age
very small,
or even zero, this is usually unwise since it will force frequent
vacuuming.
autovacuum_multixact_freeze_table_age
, toast.autovacuum_multixact_freeze_table_age
(integer)Custom vacuum_multixact_freeze_table_age parameter.
user_catalog_table
(boolean)Declare a table as an additional catalog table, e.g. for the purpose of logical replication. See the section called “Capabilities” for details.
Using OIDs in new applications is not recommended: where
possible, using a SERIAL
or other sequence
generator as the table's primary key is preferred. However, if
your application does make use of OIDs to identify specific
rows of a table, it is recommended to create a unique constraint
on the oid
column of that table, to ensure that
OIDs in the table will indeed uniquely identify rows even after
counter wraparound. Avoid assuming that OIDs are unique across
tables; if you need a database-wide unique identifier, use the
combination of tableoid
and row OID for the
purpose.
The use of OIDS=FALSE
is not recommended
for tables with no primary key, since without either an OID or a
unique data key, it is difficult to identify specific rows.
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(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.)
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 DEFAULT nextval('serial'), 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 );
The CREATE TABLE command conforms to the SQL standard, with exceptions listed below.
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.
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.
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.
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.
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™.
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.
WITH
Clause The WITH
clause is a PostgreSQL™
extension; neither storage parameters nor OIDs are in the standard.
The PostgreSQL™ concept of tablespaces is not
part of the standard. Hence, the clauses TABLESPACE
and USING INDEX TABLESPACE
are extensions.
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 these self-referencing columns explicitly, but the same effect can be had using the OID feature.