ALTER DOMAIN
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## ALTER DOMAIN

ALTER DOMAIN — change the definition of a domain

## Synopsis

    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_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. 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, verify that all data in columns using the domain 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 column data for constraint validity.

`CASCADE`

  Automatically drop objects that depend on the constraint, and in turn all objects that depend on those objects (see Section 5.13).

`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

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.

## See Also

CREATE DOMAIN, DROP DOMAIN

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