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.
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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