Specifying NOT NULL
From InterBase
Go Up to Creating Domains (Data Definition Guide)
You can optionally specify NOT NULL to force the user to enter a value. If you do not specify NOT NULL, then NULL values are allowed for any column that references this domain. NOT NULL specified on the domain level cannot be overridden by a local column definition.
Important:
If you have already specified
If you have already specified
NULL as a default value, be sure not to create contradictory constraints by also assigning NOT NULL to the domain, as in the following example:CREATE DOMAIN DOM1 INTEGER DEFAULT NULL, NOT NULL;