Index for Section DOMAIN

Alphabetical listing for C

Bottom of page

CREATE
NAME
  CREATE DOMAIN - define a new domain

SYNOPSIS
  CREATE DOMAIN domainname [AS] data_type
      [ DEFAULT default_expr ]
      [ constraint [, ... ] ]

  where constraint is:

  [ CONSTRAINT constraint_name ]
  { NOT NULL | NULL }

  PARAMETERS

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

  data_type
       The underlying data type of the domain. This may include array
       specifiers.  Refer to the User's Guide for further information about
       data types and arrays.

  DEFAULT
       The DEFAULT clause specifies a default value for columns of the domain
       data type. The value is any variable-free expression (but subselects
       are not allowed).  The data type of the default expression must match
       the data type of the domain.

       The default expression will be used in any insert operation that does
       not specify a value for the column. If there is no default for a
       domain, then the default is NULL.

       Note: If a default value is specified 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 available for compatibility with non-standard SQL
       databases. Its use is discouraged in new applications.

  OUTPUTS

  CREATE DOMAIN
       Message returned if the domain is successfully created.

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);

COMPATIBILITY
  SQL99 defines CREATE DOMAIN, but says that the only allowed constraint type
  is CHECK constraints. CHECK constraints for domains are not yet supported
  by PostgreSQL.

SEE ALSO
  DROP DOMAIN [drop_domain(5)], PostgreSQL Programmer's Guide

Index for Section DOMAIN

Alphabetical listing for C

Top of page