PostgreSQL 9.1.0 Documentation
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# ALTER DOMAIN

## Name

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
    ALTER DOMAIN name
        DROP CONSTRAINT constraint_name [ RESTRICT | CASCADE ]
    ALTER DOMAIN name
        OWNER TO new_owner
    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`

  This form adds a new constraint to a domain using the same syntax as CREATE DOMAIN. This will only succeed if all columns using the domain satisfy the new constraint.

DROP CONSTRAINT

  This form drops constraints on a domain.

OWNER

  This form changes the owner of the domain to the specified user.

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.

`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_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` and `ALTER DOMAIN SET NOT NULL` will fail if the 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 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` and `SET SCHEMA` variants, which are PostgreSQL extensions.

## See Also

CREATE DOMAIN, DROP DOMAIN

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