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.
This form adds a new constraint to a domain using the same syntax as
. This will only succeed if all columns using the domain satisfy the new constraint.
- DROP CONSTRAINT
This form drops constraints on a domain.
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.)
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;
ALTER DOMAIN conforms to the SQL standard, except for the OWNER and SET SCHEMA variants, which are PostgreSQL extensions.