Provided by: postgresql-client-8.4_8.4.11-1_amd64 bug

NAME

       CREATE DOMAIN - define a new domain

SYNOPSIS

       CREATE DOMAIN name [ AS ] data_type
           [ 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.

PARAMETERS

       name   The name (optionally schema-qualified) of a domain to be created.

       data_type
              The underlying data type of the domain. This can include array specifiers.

       DEFAULT expression
              The DEFAULT clause specifies a default value for columns of the domain  data  type.
              The  value  is  any variable-free expression (but subqueries are not allowed).  The
              data type of the default expression must match the data type of the domain.  If  no
              default value is specified, then the default value is the null value.

              The default expression will be used in any insert operation that does not specify a
              value for the column. If a default value is defined for  a  particular  column,  it
              overrides  any  default  associated  with  the  domain. In turn, the domain default
              overrides any default value associated with the underlying data type.

       CONSTRAINT constraint_name
              An optional name for a constraint. If not specified, the system generates a name.

       NOT NULL
              Values of this domain are not allowed to be null.

       NULL   Values of this domain are allowed to be null. This is the default.

              This clause is only intended for compatibility with nonstandard SQL databases.  Its
              use is discouraged in new applications.

       CHECK (expression)
              CHECK  clauses  specify  integrity  constraints or tests which values of the domain
              must satisfy.  Each constraint must be an expression producing a Boolean result. It
              should use the key word VALUE to refer to the value being tested.

              Currently, CHECK expressions cannot contain subqueries nor refer to variables other
              than VALUE.

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)]