ALTER DOMAIN
ALTER DOMAIN — change the definition of a domain
Synopsis
ALTER DOMAINname
{ SET DEFAULTexpression
| DROP DEFAULT } ALTER DOMAINname
{ SET | DROP } NOT NULL ALTER DOMAINname
ADDdomain_constraint
[ NOT VALID ] ALTER DOMAINname
DROP CONSTRAINT [ IF EXISTS ]constraint_name
[ RESTRICT | CASCADE ] ALTER DOMAINname
RENAME CONSTRAINTconstraint_name
TOnew_constraint_name
ALTER DOMAINname
VALIDATE CONSTRAINTconstraint_name
ALTER DOMAINname
OWNER TO {new_owner
| CURRENT_USER | SESSION_USER } ALTER DOMAINname
RENAME TOnew_name
ALTER DOMAINname
SET SCHEMAnew_schema
Description
ALTER DOMAIN
changes the definition of an existing domain. There are several sub-forms:
- SET/DROP DEFAULT
These forms set or remove the default value for a domain. Note that defaults only apply to subsequent
INSERT
commands; they do not affect rows already in a table using the domain.- SET/DROP NOT NULL
These forms change whether a domain is marked to allow NULL values or to reject NULL values. You can only
SET NOT NULL
when the columns using the domain contain no null values.- ADD
domain_constraint
[ NOT VALID ] This form adds a new constraint to a domain using the same syntax as CREATE DOMAIN. When a new constraint is added to a domain, all columns using that domain will be checked against the newly added constraint. These checks can be suppressed by adding the new constraint using the
NOT VALID
option; the constraint can later be made valid usingALTER DOMAIN ... VALIDATE CONSTRAINT
. Newly inserted or updated rows are always checked against all constraints, even those markedNOT VALID
.NOT VALID
is only accepted forCHECK
constraints.- DROP CONSTRAINT [ IF EXISTS ]
This form drops constraints on a domain. If
IF EXISTS
is specified and the constraint does not exist, no error is thrown. In this case a notice is issued instead.- RENAME CONSTRAINT
This form changes the name of a constraint on a domain.
- VALIDATE CONSTRAINT
This form validates a constraint previously added as
NOT VALID
, that is, it verifies that all values in table columns of the domain type satisfy the specified constraint.- OWNER
This form changes the owner of the domain to the specified user.
RENAME
This form changes the name of the domain.
- SET SCHEMA
This form changes the schema of the domain. Any constraints associated with the domain are moved into the new schema as well.
You must own the domain to use ALTER DOMAIN
. To change the schema of a domain, you must also have CREATE
privilege on the new schema. To alter the owner, you must also be a direct or indirect member of the new owning role, and that role must have CREATE
privilege on the domain's schema. (These restrictions enforce that altering the owner doesn't do anything you couldn't do by dropping and recreating the domain. However, a superuser can alter ownership of any domain anyway.)
Parameters
name
The name (possibly schema-qualified) of an existing domain to alter.
domain_constraint
New domain constraint for the domain.
constraint_name
Name of an existing constraint to drop or rename.
NOT VALID
Do not verify existing stored data for constraint validity.
CASCADE
Automatically drop objects that depend on the constraint.
RESTRICT
Refuse to drop the constraint if there are any dependent objects. This is the default behavior.
new_name
The new name for the domain.
new_constraint_name
The new name for the constraint.
new_owner
The user name of the new owner of the domain.
new_schema
The new schema for the domain.
Notes
Although ALTER DOMAIN ADD CONSTRAINT
attempts to verify that existing stored data satisfies the new constraint, this check is not bulletproof, because the command cannot “see” table rows that are newly inserted or updated and not yet committed. If there is a hazard that concurrent operations might insert bad data, the way to proceed is to add the constraint using the NOT VALID
option, commit that command, wait until all transactions started before that commit have finished, and then issue ALTER DOMAIN VALIDATE CONSTRAINT
to search for data violating the constraint. This method is reliable because once the constraint is committed, all new transactions are guaranteed to enforce it against new values of the domain type.
Currently, ALTER DOMAIN ADD CONSTRAINT
, ALTER DOMAIN VALIDATE CONSTRAINT
, and ALTER DOMAIN SET NOT NULL
will fail if the validated named domain or any derived domain is used within a composite-type column of any table in the database. They should eventually be improved to be able to verify the new constraint for such nested columns.
Examples
To add a NOT NULL
constraint to a domain:
ALTER DOMAIN zipcode SET NOT NULL;
To remove a NOT NULL
constraint from a domain:
ALTER DOMAIN zipcode DROP NOT NULL;
To add a check constraint to a domain:
ALTER DOMAIN zipcode ADD CONSTRAINT zipchk CHECK (char_length(VALUE) = 5);
To remove a check constraint from a domain:
ALTER DOMAIN zipcode DROP CONSTRAINT zipchk;
To rename a check constraint on a domain:
ALTER DOMAIN zipcode RENAME CONSTRAINT zipchk TO zip_check;
To move the domain into a different schema:
ALTER DOMAIN zipcode SET SCHEMA customers;
Compatibility
ALTER DOMAIN
conforms to the SQL standard, except for the OWNER
, RENAME
, SET SCHEMA
, and VALIDATE CONSTRAINT
variants, which are PostgreSQL extensions. The NOT VALID
clause of the ADD CONSTRAINT
variant is also a PostgreSQL extension.