create_domain man page on Scientific

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       CREATE DOMAIN - define a new domain

       CREATE DOMAIN name [ AS ] data_type
	   [ DEFAULT expression ]
	   [ constraint [ ... ] ]

       where constraint is:

       [ CONSTRAINT constraint_name ]
       { NOT NULL | NULL | CHECK (expression) }

       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 con‐
       tain 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.

       name   The name (optionally schema-qualified) of a domain  to  be  cre‐

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

       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	 asso‐
	      ciated  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

	      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 val‐
	      ues 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.

       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
	  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,
	 postal us_postal_code NOT NULL

       The command CREATE DOMAIN conforms to the SQL standard.

       ALTER DOMAIN [alter_domain(7)], DROP DOMAIN [drop_domain(7)]

SQL - Language Statements	  2013-10-08		      CREATE DOMAIN(7)

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