CREATE DOMAIN(SQL - Language Statements (2002-11-CREATE DOMAIN(l)
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.
Page 1 (printed 3/24/03)
CREATE DOMAIN(SQL - Language Statements (2002-11-CREATE DOMAIN(l)
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(l)], PostgreSQL Programmer's Guide
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