Description
CREATE DOMAIN allows the user to register a new
data domain with PostgreSQL for use in the
current data base. The user who defines a domain becomes its owner.
If a schema name is given (for example, CREATE DOMAIN
myschema.mydomain ...) then the domain is created in the
specified schema. Otherwise it is created in the current schema (the one
at the front of the search path; see CURRENT_SCHEMA()).
The domain name must be unique among the types and domains existing
in its schema.
Domains are useful for abstracting common fields between tables into
a single location for maintenance. An email address column may be used
in several tables, all with the same properties. Define a domain and
use that rather than setting up each table's constraints individually.
Examples
This example creates the country_code data type and then uses the
type in a table definition:
CREATE DOMAIN country_code char(2) NOT NULL;
CREATE TABLE countrylist (id INT4, country country_code);
