PostgreSQL 7.4 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

## 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 may 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.

You must own the domain to use `ALTER DOMAIN`; except for `ALTER DOMAIN OWNER`, which may only be executed by a superuser.

## 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.

## 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;

## Compatibility

The `ALTER DOMAIN` statement is compatible with SQL99, except for the OWNER variant, which is a PostgreSQL extension.

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