NAME¶

CREATE_DOMAIN - define a new domain

SYNOPSIS¶

CREATE DOMAIN name [ AS ] data_type


    [ COLLATE collation ]


    [ DEFAULT expression ]


    [ constraint [ ... ] ]
where constraint is:
[ CONSTRAINT constraint_name ]
{ NOT NULL | NULL | CHECK (expression) }

DESCRIPTION¶

CREATE DOMAIN creates a new domain. A domain is essentially a data type with optional constraints (restrictions on the allowed set of values). 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 domain name must be unique among the types and domains existing in its schema.

Domains are useful for abstracting common constraints on fields into a single location for maintenance. For example, several tables might contain email address columns, all requiring the same CHECK constraint to verify the address syntax. Define a domain rather than setting up each table's constraint individually.

To be able to create a domain, you must have USAGE privilege on the underlying type.

PARAMETERS¶

name

data_type

collation

DEFAULT expression

CONSTRAINT constraint_name

NOT NULL

NULL

CHECK (expression)

EXAMPLES¶

This example creates the us_postal_code data type and then uses the type in a table definition. A regular expression test is used to verify that the value looks like a valid US postal code:

CREATE DOMAIN us_postal_code AS TEXT
CHECK(


   VALUE ~ '^\d{5}$'
OR VALUE ~ '^\d{5}-\d{4}$'
);
CREATE TABLE us_snail_addy (


  address_id SERIAL PRIMARY KEY,


  street1 TEXT NOT NULL,


  street2 TEXT,


  street3 TEXT,


  city TEXT NOT NULL,


  postal us_postal_code NOT NULL
);

COMPATIBILITY¶

The command CREATE DOMAIN conforms to the SQL standard.

SEE ALSO¶

ALTER DOMAIN (ALTER_DOMAIN(7)), DROP DOMAIN (DROP_DOMAIN(7))