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RedHat 9 (Linux i386) - man page for create_domain (redhat section 7)

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       CREATE DOMAIN - define a new domain

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

       where constraint is:

       [ CONSTRAINT constraint_name ]
       { NOT NULL | NULL }

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

	      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.

	      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

	      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.

	      Message returned if the domain is successfully created.

       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

       This example creates the country_code data type and then uses the type in a table  defini-

       CREATE DOMAIN country_code char(2) NOT NULL;
       CREATE TABLE countrylist (id INT4, country country_code);

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

       DROP DOMAIN [drop_domain(7)], PostgreSQL Programmer's Guide

SQL - Language Statements		    2002-11-22				 CREATE DOMAIN(7)
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