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 default values only apply to subsequent INSERT commands; they do not affect rows already existing in tables that use the domain.
SET/DROP NOT NULL
These forms change whether a domain is marked to allow or reject NULL values. SET NOT NULL can only be used when 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 the domain will be checked against the newly added constraint. This check can be suppressed by adding the new constraint with the NOT VALID option, and the constraint can later be validated using ALTER DOMAIN ... VALIDATE CONSTRAINT. Newly inserted and updated rows are always checked against all constraints (including those marked as NOT VALID). Only CHECK constraints accept NOT VALID.
DROP CONSTRAINT [ IF EXISTS ]
This form drops a constraint 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 that was previously added as NOT VALID, that is, it verifies that all values in table columns of the domain type 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 also moved to the new schema.
To use ALTER DOMAIN, you must own the domain. To change the schema of a domain, you must also have CREATE privilege on the new schema. To change 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 changing the owner cannot do anything you couldn't do by dropping and recreating the domain. However, a superuser can change ownership of any domain).
Parameters
name
The name (optionally schema-qualified) of an existing domain to modify.
domain_constraint
A new domain constraint for the domain.
constraint_name
The name of an existing constraint to drop or rename.
NOT VALID
Do not verify the validity of the constraint against existing stored data.
CASCADE
Automatically drop objects that depend on the constraint, and in turn all objects that depend on those objects.
RESTRICT
Refuse to drop the constraint if there are any dependent objects. This is the default behavior.
new_name
The new name of the domain.
new_constraint_name
The new name of the constraint.
new_owner
The user name of the new owner of the domain.
new_schema
The new schema for the domain.
Notes
Although ALTER DOMAIN ADD CONSTRAINT attempts to verify that existing stored data satisfies the new constraint, this check is not foolproof because the command cannot "see" newly inserted or updated table rows that have not yet been committed. If there is a risk of concurrent operations inserting bad data, the approach is to add the constraint using the NOT VALID option, commit the command, wait until all transactions that started before the commit have finished, and then issue ALTER DOMAIN VALIDATE CONSTRAINT to search for data violating the constraint. This method is reliable because once the constraint is committed, all new transactions are guaranteed to enforce the constraint for new values of the domain type. Currently, ALTER DOMAIN ADD CONSTRAINT, ALTER DOMAIN VALIDATE CONSTRAINT, and ALTER DOMAIN SET NOT NULL will fail if the domain or any derived domain is used by any container-type column (composite, array, or range type column) of any table in the database. These commands will eventually be improved to perform constraint validation on such nested values.
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 to a different schema:
ALTER DOMAIN zipcode SET SCHEMA customers;