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CREATE TABLE

Name

CREATE TABLE  --  Creates a new table

Synopsis

CREATE [ TEMPORARY | TEMP ] TABLE table_name (
    { column_name type [ column_constraint [ ... ] ]
      | table_constraint }  [, ... ]
    ) [ INHERITS ( parent_table [, ... ] ) ]

where column_constraint can be:
[ CONSTRAINT constraint_name ]
{ NOT NULL | NULL | UNIQUE | PRIMARY KEY | DEFAULT value | CHECK (condition) |
  REFERENCES table [ ( column ) ] [ MATCH FULL | MATCH PARTIAL ]
   [ ON DELETE action ] [ ON UPDATE action ]
   [ DEFERRABLE | NOT DEFERRABLE ] [ INITIALLY DEFERRED | INITIALLY IMMEDIATE ]
}

and table_constraint can be:
[ CONSTRAINT constraint_name ]
{ UNIQUE ( column_name [, ... ] ) |
  PRIMARY KEY ( column_name [, ... ] ) |
  CHECK ( condition ) |
  FOREIGN KEY ( column_name [, ... ] ) REFERENCES table [ ( column [, ... ] ) ]
   [ MATCH FULL | MATCH PARTIAL ] [ ON DELETE action ] [ ON UPDATE action ]
   [ DEFERRABLE | NOT DEFERRABLE ] [ INITIALLY DEFERRED | INITIALLY IMMEDIATE ]
}
  

Inputs

TEMPORARY or TEMP

If specified, the table is created only for this session, and is automatically dropped on session exit. Existing permanent tables with the same name are not visible (in this session) while the temporary table exists. Any indexes created on a temporary table are automatically temporary as well.

table_name

The name of the new table to be created.

column_name

The name of a column to be created in the new table.

type

The type of the column. This may include array specifiers. Refer to the PostgreSQL User's Guide for further information about data types and arrays.

parent_table

The optional INHERITS clause specifies a list of table names from which this table automatically inherits all fields.

constraint_name

An optional name for a column or table constraint. If not specified, the system generates a name.

value

A default value for a column. See the DEFAULT clause for more information.

condition

CHECK clauses specify integrity constraints or tests which new or updated rows must satisfy for an insert or update operation to succeed. Each constraint must be an expression producing a boolean result. A condition appearing within a column definition should reference that column's value only, while a condition appearing as a table constraint may reference multiple columns.

table

The name of an existing table to be referenced by a foreign key constraint.

column

The name of a column in an existing table to be referenced by a foreign key constraint. If not specified, the primary key of the existing table is assumed.

action

A keyword indicating the action to take when a foreign key constraint is violated.

Outputs

CREATE

Message returned if table is successfully created.

ERROR

Message returned if table creation failed. This is usually accompanied by some descriptive text, such as: ERROR: Relation 'table' already exists , which occurs at runtime if the table specified already exists in the database.

Description

CREATE TABLE will enter a new, initially empty table into the current database. The table will be "owned" by the user issuing the command.

Each type may be a simple type, a complex type (set) or an array type. Each attribute may be specified to be non-null and each may have a default value, specified by the DEFAULT Clause.

Note: Consistent array dimensions within an attribute are not enforced. This will likely change in a future release.

CREATE TABLE also automatically creates a data type that represents the tuple type (structure type) corresponding to one row of the table. Therefore, tables can't have the same name as any existing datatype.

A table can have no more than 1600 columns (in practice, the effective limit is lower because of tuple-length constraints). A table cannot have the same name as a system catalog table.

INHERITS Clause

INHERITS ( parent_table [, ... ] )
   

The optional INHERITS clause specifies a list of table names from which the new table automatically inherits all fields. If the same field name appears in more than one parent table, Postgres reports an error unless the field definitions match in each of the parent tables. If there is no definition conflict, then the duplicate fields are merged to form a single field of the new table. If the new table's own field list contains a field name that is also inherited, this declaration must likewise match the inherited field(s), and the field definitions are merged into one.

Inherited and new field declarations of the same name must specify exactly the same data type to avoid an error. They need not specify identical constraints --- all constraints provided from any declaration are merged together and all are applied to the new table. If the new table explicitly specifies a default value for the field, this default overrides any defaults from inherited declarations of the field. Otherwise, any parents that specify default values for the field must all specify the same default, or an error will be reported.

Postgres automatically allows the created table to inherit functions on tables above it in the inheritance hierarchy; that is, if we create table foo inheriting from bar, then functions that accept the tuple type bar can also be applied to instances of foo. (Currently, this works reliably for functions on the first or only parent table, but not so well for functions on additional parents.)

DEFAULT Clause

DEFAULT value
   

The DEFAULT clause assigns a default data value for the column whose column definition it appears within. The value is any variable-free expression (note that sub-selects and cross-references to other columns in the current table are not supported). The data type of a default value must match the column definition's data type.

The DEFAULT expression will be used in any INSERT operation that does not specify a value for the column. If there is no DEFAULT clause, then the default is NULL.

Usage

CREATE TABLE distributors (
    name     VARCHAR(40) DEFAULT 'luso films',
    did      INTEGER  DEFAULT NEXTVAL('distributors_serial'),
    modtime  TIMESTAMP DEFAULT now()
);
    
The above assigns a literal constant default value for the column name, and arranges for the default value of column did to be generated by selecting the next value of a sequence object. The default value of modtime will be the time at which the row is inserted.

It is worth remarking that

    modtime  TIMESTAMP DEFAULT 'now'
    
would produce a result that is probably not the intended one: the string 'now' will be coerced to a timestamp value immediately, and so the default value of modtime will always be the time of table creation. This difficulty is avoided by specifying the default value as a function call.

Column Constraints

[ CONSTRAINT constraint_name ] {
    NULL | NOT NULL | UNIQUE | PRIMARY KEY | CHECK condition |
    REFERENCES reftable [ ( refcolumn ) ]
     [ MATCH matchtype ]
     [ ON DELETE action ] 
     [ ON UPDATE action ]
     [ [ NOT ] DEFERRABLE ] 
     [ INITIALLY checktime ] }
   

Inputs

constraint_name

An arbitrary name given to a constraint clause.

NULL

The column is allowed to contain NULL values. This is the default.

NOT NULL

The column is not allowed to contain NULL values. This is equivalent to the column constraint CHECK (column NOT NULL).

UNIQUE

The column must have unique values. In Postgres this is enforced by automatic creation of a unique index on the column.

PRIMARY KEY

This column is a primary key, which implies that other tables may rely on this column as a unique identifier for rows. Both UNIQUE and NOT NULL are implied by PRIMARY KEY. See PRIMARY KEY for more information.

condition

An arbitrary boolean-valued constraint condition.

Description

The optional constraint clauses specify constraints or tests which new or updated rows must satisfy for an insert or update operation to succeed.

A constraint is a named rule: an SQL object which helps define valid sets of values by putting limits on the results of INSERT, UPDATE or DELETE operations performed on a table.

There are two ways to define integrity constraints: table constraints, covered later, and column constraints, covered here.

A column constraint is an integrity constraint defined as part of a column definition, and logically becomes a table constraint as soon as it is created. The column constraints available are:

PRIMARY KEY
REFERENCES
UNIQUE
CHECK
NOT NULL

NOT NULL Constraint

[ CONSTRAINT name ] NOT NULL 
   

The NOT NULL constraint specifies a rule that a column may contain only non-null values. This is a column constraint only, and not allowed as a table constraint.

Outputs

status
ERROR: ExecAppend: Fail to add null value in not null attribute "column".

This error occurs at runtime if one tries to insert a null value into a column which has a NOT NULL constraint.

Description

Usage

Define two NOT NULL column constraints on the table distributors, one of which is explicitly given a name:

CREATE TABLE distributors (
    did      DECIMAL(3) CONSTRAINT no_null NOT NULL,
    name     VARCHAR(40) NOT NULL
);
     

UNIQUE Constraint

[ CONSTRAINT constraint_name ] UNIQUE
   

Inputs

constraint_name

An arbitrary name given to a constraint clause.

Outputs

status
ERROR: Cannot insert a duplicate key into a unique index.

This error occurs at runtime if one tries to insert a duplicate value into a column.

Description

The UNIQUE constraint specifies a rule that a group of one or more distinct columns of a table may contain only unique values.

The column definitions of the specified columns do not have to include a NOT NULL constraint to be included in a UNIQUE constraint. Having more than one null value in a column without a NOT NULL constraint, does not violate a UNIQUE constraint. (This deviates from the SQL92 definition, but is a more sensible convention. See the section on compatibility for more details.)

Each UNIQUE column constraint must name a column that is different from the set of columns named by any other UNIQUE or PRIMARY KEY constraint defined for the table.

Note: Postgres automatically creates a unique index for each UNIQUE constraint, to assure data integrity. See CREATE INDEX for more information.

Usage

Defines a UNIQUE constraint for the name column:

CREATE TABLE distributors (
    did      DECIMAL(3),
    name     VARCHAR(40) UNIQUE
);
  
which is equivalent to the following specified as a table constraint:
CREATE TABLE distributors (
    did      DECIMAL(3),
    name     VARCHAR(40),
    UNIQUE(name)
);
     

The CHECK Constraint

[ CONSTRAINT constraint_name ] CHECK ( condition )
   

Inputs

constraint_name

An arbitrary name given to a constraint clause.

condition

Any valid conditional expression evaluating to a boolean result.

Outputs

status

ERROR: ExecAppend: rejected due to CHECK constraint "constraint_name".

This error occurs at runtime if one tries to insert an illegal value into a column subject to a CHECK constraint.

Description

The CHECK constraint specifies a generic restriction on allowed values within a column. The CHECK constraint is also allowed as a table constraint.

CHECK specifies a general boolean expression involving one or more columns of a table. A new row will be rejected if the boolean expression evaluates to FALSE when applied to the row's values.

Currently, CHECK expressions cannot contain sub-selects nor refer to variables other than fields of the current row.

The SQL92 standard says that CHECK column constraints may only refer to the column they apply to; only CHECK table constraints may refer to multiple columns. Postgres does not enforce this restriction. It treats column and table CHECK constraints alike.

PRIMARY KEY Constraint

[ CONSTRAINT constraint_name ] PRIMARY KEY 
   

Inputs

constraint_name

An arbitrary name given to a constraint clause.

Outputs

ERROR: Cannot insert a duplicate key into a unique index.

This occurs at runtime if one tries to insert a duplicate value into a column subject to a PRIMARY KEY constraint.

Description

The PRIMARY KEY column constraint specifies that a column of a table may contain only unique (non-duplicate), non-NULL values. The definition of the specified column does not have to include an explicit NOT NULL constraint to be included in a PRIMARY KEY constraint.

Only one PRIMARY KEY can be specified for a table, whether as a column constraint or a table constraint.

Notes

Postgres automatically creates a unique index to assure data integrity (see CREATE INDEX statement).

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, since it will result in duplication of equivalent indexes and unproductive additional runtime overhead. However, Postgres does not specifically disallow this.

REFERENCES Constraint

[ CONSTRAINT constraint_name ] REFERENCES reftable [ ( refcolumn ) ] 
    [ MATCH matchtype ]
    [ ON DELETE action ] 
    [ ON UPDATE action ]
    [ [ NOT ] DEFERRABLE ] 
    [ INITIALLY checktime ]
   

The REFERENCES constraint specifies a rule that a column value is checked against the values of another column. REFERENCES can also be specified as part of a FOREIGN KEY table constraint.

Inputs

constraint_name

An arbitrary name given to a constraint clause.

reftable

The table that contains the data to check against.

refcolumn

The column in reftable to check the data against. If this is not specified, the PRIMARY KEY of the reftable is used.

MATCH matchtype

There are three match types: MATCH FULL, MATCH PARTIAL, and a default match type if none is specified. MATCH FULL will not allow one column of a multi-column foreign key to be NULL unless all foreign key columns are NULL. The default MATCH type allows some foreign key columns to be NULL while other parts of the foreign key are not NULL. MATCH PARTIAL is currently not supported.

ON DELETE action

The action to do when a referenced row in the referenced table is being deleted. There are the following actions.

NO ACTION

Produce error if foreign key violated. This is the default.

RESTRICT

Same as NO ACTION.

CASCADE

Delete any rows referencing the deleted row.

SET NULL

Set the referencing column values to NULL.

SET DEFAULT

Set the referencing column values to their default value.

ON UPDATE action

The action to do 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 changed, no action is done. There are the following actions.

NO ACTION

Produce error if foreign key violated. This is the default.

RESTRICT

Same as NO ACTION.

CASCADE

Update the value of the referencing column to the new value of the referenced column.

SET NULL

Set the referencing column values to NULL.

SET DEFAULT

Set the referencing column values to their default value.

[ NOT ] DEFERRABLE

This controls whether the constraint can be deferred to the end of the transaction. If DEFERRABLE, SET CONSTRAINTS ALL DEFERRED will cause the foreign key to be checked only at the end of the transaction. NOT DEFERRABLE is the default.

INITIALLY checktime

checktime has two possible values which specify the default time to check the constraint.

DEFERRED

Check constraint only at the end of the transaction.

IMMEDIATE

Check constraint after each statement. This is the default.

Outputs

status
ERROR: name referential integrity violation - key referenced from table not found in reftable

This error occurs at runtime if one tries to insert a value into a column which does not have a matching column in the referenced table.

Description

The REFERENCES column constraint specifies that a column of a table must only contain values which match against values in a referenced column of a referenced table.

A value added to this column is matched against the values of the referenced table and referenced column using the given match type. In addition, when the referenced column data is changed, actions are run upon this column's matching data.

Notes

Currently Postgres only supports MATCH FULL and a default match type. In addition, the referenced columns are supposed to be the columns of a UNIQUE constraint in the referenced table, however Postgres does not enforce this.

Table Constraints

[ CONSTRAINT name ] { PRIMARY KEY |  UNIQUE } ( column [, ... ] )
[ CONSTRAINT name ] CHECK ( constraint )
[ CONSTRAINT name ] FOREIGN KEY ( column [, ... ] ) 
                     REFERENCES reftable [ ( refcolumn [, ... ] ) ]
                      [ MATCH matchtype ] 
                      [ ON DELETE action ] 
                      [ ON UPDATE action ]
                      [ [ NOT ] DEFERRABLE ] 
                      [ INITIALLY checktime ]
   

Inputs

constraint_name

An arbitrary name given to a constraint clause.

column [, ... ]

The column name(s) for which to define a unique index and, for PRIMARY KEY, a NOT NULL constraint.

CHECK ( constraint )

A boolean expression to be evaluated as the constraint.

Outputs

The possible outputs for the table constraint clause are the same as for the corresponding portions of the column constraint clause.

Description

A table constraint is an integrity constraint defined on one or more columns of a table. The four variations of "Table Constraint" are:

UNIQUE
CHECK
PRIMARY KEY
FOREIGN KEY

UNIQUE Constraint

[ CONSTRAINT constraint_name ] UNIQUE ( column [, ... ] )
    

Inputs

constraint_name

An arbitrary name given to a constraint clause.

column

A name of a column in a table.

Outputs

status
ERROR: Cannot insert a duplicate key into a unique index

This error occurs at runtime if one tries to insert a duplicate value into a column.

Description

The UNIQUE constraint specifies a rule that a group of one or more distinct columns of a table may 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.

See the section on the UNIQUE column constraint for more details.

Usage

Prevent duplicate rows in the table distributors:

CREATE TABLE distributors (
    did      DECIMAL(3),
    name     VARCHAR(40),
    UNIQUE(did,name)
);
     

PRIMARY KEY Constraint

[ CONSTRAINT constraint_name ] PRIMARY KEY ( column [, ... ] ) 
    

Inputs

constraint_name

An arbitrary name given to a constraint clause.

column [, ... ]

The names of one or more columns in the table.

Outputs

status
ERROR: Cannot insert a duplicate key into a unique index.

This occurs at run-time if one tries to insert a duplicate value into a column subject to a PRIMARY KEY constraint.

Description

The PRIMARY KEY constraint specifies a rule that a group of one or more distinct columns of a table may contain only unique (nonduplicate), non-null values. The column definitions of the specified columns do not have to include a NOT NULL constraint to be included in a PRIMARY KEY constraint.

The PRIMARY KEY table constraint is similar to that for column constraints, with the additional capability of encompassing multiple columns.

Refer to the section on the PRIMARY KEY column constraint for more information.

REFERENCES Constraint

[ CONSTRAINT constraint_name ] FOREIGN KEY ( column [, ... ] )
    REFERENCES reftable [ ( refcolumn [, ... ] ) ] 
    [ MATCH matchtype ]
    [ ON DELETE action ] 
    [ ON UPDATE action ]
    [ [ NOT ] DEFERRABLE ]
    [ INITIALLY checktime ]
   

The REFERENCES constraint specifies a rule that a column value or set of column values is checked against the values in another table.

Inputs

constraint_name

An arbitrary name given to a constraint clause.

column [, ... ]

The names of one or more columns in the table.

reftable

The table that contains the data to check against.

referenced column [, ... ]

One or more columns in the reftable to check the data against. If this is not specified, the PRIMARY KEY of the reftable is used.

MATCH matchtype

There are three match types: MATCH FULL, MATCH PARTIAL, and a default match type if none is specified. MATCH FULL will not allow one column of a multi-column foreign key to be NULL unless all foreign key columns are NULL. The default MATCH type allows some foreign key columns to be NULL while other parts of the foreign key are not NULL. MATCH PARTIAL is currently not supported.

ON DELETE action

The action to do when a referenced row in the referenced table is being deleted. There are the following actions.

NO ACTION

Produce error if foreign key violated. This is the default.

RESTRICT

Same as NO ACTION.

CASCADE

Delete any rows referencing the deleted row.

SET NULL

Set the referencing column values to NULL.

SET DEFAULT

Set the referencing column values to their default value.

ON UPDATE action

The action to do 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 changed, no action is done. There are the following actions.

NO ACTION

Produce error if foreign key violated. This is the default.

RESTRICT

Disallow update of row being referenced.

CASCADE

Update the value of the referencing column to the new value of the referenced column.

SET NULL

Set the referencing column values to NULL.

SET DEFAULT

Set the referencing column values to their default value.

[ NOT ] DEFERRABLE

This controls whether the constraint can be deferred to the end of the transaction. If DEFERRABLE, SET CONSTRAINTS ALL DEFERRED will cause the foreign key to be checked only at the end of the transaction. NOT DEFERRABLE is the default.

INITIALLY checktime

checktime has two possible values which specify the default time to check the constraint.

IMMEDIATE

Check constraint after each statement. This is the default.

DEFERRED

Check constraint only at the end of the transaction.

Outputs

status
ERROR: name referential integrity violation - key referenced from table not found in reftable

This error occurs at runtime if one tries to insert a value into a column which does not have a matching column in the referenced table.

Description

The FOREIGN KEY constraint specifies a rule that a group of one or more distinct columns of a table is related to a group of distinct columns in the referenced table.

The FOREIGN KEY table constraint is similar to that for column constraints, with the additional capability of encompassing multiple columns.

Refer to the section on the FOREIGN KEY column constraint for more information.

Usage

Create table films and table distributors:

CREATE TABLE films (
     code      CHARACTER(5) CONSTRAINT firstkey PRIMARY KEY,
     title     CHARACTER VARYING(40) NOT NULL,
     did       DECIMAL(3) NOT NULL,
     date_prod DATE,
     kind      CHAR(10),
     len       INTERVAL HOUR TO MINUTE
);
   
CREATE TABLE distributors (
     did      DECIMAL(3) PRIMARY KEY DEFAULT NEXTVAL('serial'),
     name     VARCHAR(40) NOT NULL CHECK (name <> '')
);
   

Create a table with a 2-dimensional array:

   CREATE TABLE array (
          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       DECIMAL(3),
    date_prod DATE,
    kind      CHAR(10),
    len       INTERVAL HOUR TO MINUTE,
    CONSTRAINT production UNIQUE(date_prod)
);
   

Define a CHECK column constraint:

CREATE TABLE distributors (
    did      DECIMAL(3) CHECK (did > 100),
    name     VARCHAR(40)
);
   

Define a CHECK table constraint:

CREATE TABLE distributors (
    did      DECIMAL(3),
    name     VARCHAR(40)
    CONSTRAINT con1 CHECK (did > 100 AND name > '')
);
   

Define a PRIMARY KEY table constraint for the table films. PRIMARY KEY table constraints can be defined on one or more columns of the table:

CREATE TABLE films (
    code      CHAR(5),
    title     VARCHAR(40),
    did       DECIMAL(3),
    date_prod DATE,
    kind      CHAR(10),
    len       INTERVAL HOUR TO MINUTE,
    CONSTRAINT code_title PRIMARY KEY(code,title)
);
   

Defines a PRIMARY KEY column constraint for table distributors. PRIMARY KEY column constraints can only be defined on one column of the table (the following two examples are equivalent):

CREATE TABLE distributors (
    did      DECIMAL(3),
    name     CHAR VARYING(40),
    PRIMARY KEY(did)
); 
   
CREATE TABLE distributors (
    did      DECIMAL(3) PRIMARY KEY,
    name     VARCHAR(40)
);
   

Compatibility

SQL92

In addition to the locally visible temporary table, SQL92 also defines a CREATE GLOBAL TEMPORARY TABLE statement, and optionally an ON COMMIT clause:

CREATE GLOBAL TEMPORARY TABLE table ( column type [
    DEFAULT value ] [ CONSTRAINT column_constraint ] [, ... ] )
    [ CONSTRAINT table_constraint ] [ ON COMMIT { DELETE | PRESERVE } ROWS ] 
   

For temporary tables, the CREATE GLOBAL TEMPORARY TABLE statement names a new table visible to other clients and defines the table's columns and constraints.

The optional ON COMMIT clause of CREATE TEMPORARY TABLE specifies whether or not the temporary table should be emptied of rows whenever COMMIT is executed. If the ON COMMIT clause is omitted, SQL92 specifies that the default is ON COMMIT DELETE ROWS. However, Postgres' behavior is always like ON COMMIT PRESERVE ROWS.

UNIQUE clause

SQL92 specifies some additional capabilities for UNIQUE:

Table Constraint definition:

[ CONSTRAINT constraint_name ] UNIQUE ( column [, ... ] )
    [ { INITIALLY DEFERRED | INITIALLY IMMEDIATE } ]
    [ [ NOT ] DEFERRABLE ]
     

Column Constraint definition:

[ CONSTRAINT constraint_name ] UNIQUE
      [ {INITIALLY DEFERRED | INITIALLY IMMEDIATE} ]
      [ [ NOT ] DEFERRABLE ]
     

NULL clause

The NULL "constraint" (actually a non-constraint) is a Postgres extension to SQL92 that is included for symmetry with the NOT NULL clause (and for compatibility with some other RDBMSes). Since it is the default for any column, its presence is simply noise.

[ CONSTRAINT constraint_name ] NULL 
     

NOT NULL clause

SQL92 specifies some additional capabilities for NOT NULL:

[ CONSTRAINT constraint_name ] NOT NULL 
    [ {INITIALLY DEFERRED | INITIALLY IMMEDIATE} ]
    [ [ NOT ] DEFERRABLE ]
     

CONSTRAINT clause

SQL92 specifies some additional capabilities for constraints, and also defines assertions and domain constraints.

Note: Postgres does not yet support either domains or assertions.

An assertion is a special type of integrity constraint and shares the same namespace as other constraints. However, an assertion is not necessarily dependent on one particular table as constraints are, so SQL-92 provides the CREATE ASSERTION statement as an alternate method for defining a constraint:

CREATE ASSERTION name CHECK ( condition )
    

Domain constraints are defined by CREATE DOMAIN or ALTER DOMAIN statements:

Domain constraint:

[ CONSTRAINT constraint_name ] CHECK constraint 
    [ {INITIALLY DEFERRED | INITIALLY IMMEDIATE} ]
    [ [ NOT ] DEFERRABLE ]
     

Table constraint definition:

[ CONSTRAINT constraint_name ] { PRIMARY KEY ( column, ... ) | FOREIGN KEY constraint | UNIQUE constraint | CHECK constraint }
    [ {INITIALLY DEFERRED | INITIALLY IMMEDIATE} ]
    [ [ NOT ] DEFERRABLE ]
     

Column constraint definition:

[ CONSTRAINT constraint_name ] { NOT NULL | PRIMARY KEY | FOREIGN KEY constraint | UNIQUE | CHECK constraint }  
    [ {INITIALLY DEFERRED | INITIALLY IMMEDIATE} ]
    [ [ NOT ] DEFERRABLE ]
     

A CONSTRAINT definition may contain one deferment attribute clause and/or one initial constraint mode clause, in any order.

NOT DEFERRABLE

The constraint must be checked at the end of each statement. SET CONSTRAINTS ALL DEFERRED will have no effect on this type of constraint.

DEFERRABLE

This controls whether the constraint can be deferred to the end of the transaction. If SET CONSTRAINTS ALL DEFERRED is used or the constraint is set to INITIALLY DEFERRED, this will cause the foreign key to be checked only at the end of the transaction.

Note: SET CONSTRAINTS changes the foreign key constraint mode only for the current transaction.

INITIALLY IMMEDIATE

Check constraint after each statement. This is the default.

INITIALLY DEFERRED

Check constraint only at the end of the transaction.

CHECK clause

SQL92 specifies some additional capabilities for CHECK in either table or column constraints.

table constraint definition:

[ CONSTRAINT constraint_name ] CHECK ( VALUE condition ) 
      [ {INITIALLY DEFERRED | INITIALLY IMMEDIATE} ]
      [ [ NOT ] DEFERRABLE ]
     

column constraint definition:

[ CONSTRAINT constraint_name ] CHECK ( VALUE condition ) 
      [ {INITIALLY DEFERRED | INITIALLY IMMEDIATE} ]
      [ [ NOT ] DEFERRABLE ]
    

PRIMARY KEY clause

SQL92 specifies some additional capabilities for PRIMARY KEY:

Table Constraint definition:

[ CONSTRAINT constraint_name ] PRIMARY KEY ( column [, ... ] ) 
    [ {INITIALLY DEFERRED | INITIALLY IMMEDIATE} ]
    [ [ NOT ] DEFERRABLE ]
     

Column Constraint definition:

[ CONSTRAINT constraint_name ] PRIMARY KEY 
    [ {INITIALLY DEFERRED | INITIALLY IMMEDIATE} ]
    [ [ NOT ] DEFERRABLE ]
     

Inheritance

Multiple inheritance via the INHERITS clause is a Postgres language extension. SQL99 (but not SQL92) defines single inheritance using a different syntax and different semantics. SQL99-style inheritance is not yet supported by Postgres.

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