ALTER DOMAIN

ALTER DOMAIN

7

SQL - Language Statements

ALTER DOMAIN

change the definition of a domain

ALTER DOMAIN

name

{ SET DEFAULT

expression

\| DROP DEFAULT } ALTER DOMAIN

name

{ SET \| DROP } NOT NULL ALTER DOMAIN

name

ADD

domain\_constraint

\[ NOT VALID \] ALTER DOMAIN

name

DROP CONSTRAINT \[ IF EXISTS \]

constraint\_name

\[ RESTRICT \| CASCADE \] ALTER DOMAIN

name

RENAME CONSTRAINT

constraint\_name

TO

new\_constraint\_name

ALTER DOMAIN

name

VALIDATE CONSTRAINT

constraint\_name

ALTER DOMAIN

name

OWNER TO {

new\_owner

\| CURRENT\_ROLE \| CURRENT\_USER \| SESSION\_USER } ALTER DOMAIN

name

RENAME TO

new\_name

ALTER DOMAIN

name

SET SCHEMA

new\_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`](#sql-createdomain). 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 using `ALTER DOMAIN ... VALIDATE CONSTRAINT`.
    Newly inserted or updated rows are always checked against all
    constraints, even those marked `NOT VALID`. `NOT VALID` is only
    accepted for `CHECK` 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, and in
    turn all objects that depend on those objects (see
    [???](#ddl-depend)).

`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 named domain or any derived domain is used
within a container-type column (a composite, array, or range column) in
any table in the database. They should eventually be improved to be able
to verify the new constraint for such nested values.

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 {#sql-alterdomain-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.

See Also {#sql-alterdomain-see-also}
========
