Index for Section DOMAIN

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CREATE
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 data domain. 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 fields between tables into a
  single location for maintenance. For example, 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.

PARAMETERS
  name 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.

  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 name 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 NOT NULL 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(5)], DROP DOMAIN [drop_domain(l)]

Index for Section DOMAIN

Alphabetical listing for C

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