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<!--
$Header: /cvsroot/pgsql/doc/src/sgml/ref/create_domain.sgml,v 1.1 2002/03/06 20:34:44 momjian Exp $
PostgreSQL documentation
-->
<refentry id="SQL-CREATEDOMAIN">
<refmeta>
<refentrytitle id="sql-createdomian-title">
CREATE DOMAIN
</refentrytitle>
<refmiscinfo>SQL - Language Statements</refmiscinfo>
</refmeta>
<refnamediv>
<refname>
CREATE DOMAIN
</refname>
<refpurpose>
define a new domain
</refpurpose>
</refnamediv>
<refsynopsisdiv>
<refsynopsisdivinfo>
<date>2002-02-24</date>
</refsynopsisdivinfo>
<synopsis>
CREATE DOMAIN <replaceable class="parameter">domainname</replaceable> <replaceable class="parameter">data_type</replaceable> [ DEFAULT <replaceable>default_expr</> ] [ <replaceable class="PARAMETER">column_constraint</replaceable> [, ... ] ]
[ CONSTRAINT <replaceable class="PARAMETER">constraint_name</replaceable> ]
{ NOT NULL | NULL <!-- | UNIQUE | PRIMARY KEY |
CHECK (<replaceable class="PARAMETER">expression</replaceable>) |
REFERENCES <replaceable class="PARAMETER">reftable</replaceable> [ ( <replaceable class="PARAMETER">refcolumn</replaceable> ) ] [ MATCH FULL | MATCH PARTIAL ]
[ ON DELETE <replaceable class="parameter">action</replaceable> ] [ ON UPDATE <replaceable class="parameter">action</replaceable> ] --> }
<!-- [ DEFERRABLE | NOT DEFERRABLE ] [ INITIALLY DEFERRED | INITIALLY IMMEDIATE ] -->
</synopsis>
<refsect2 id="R2-SQL-CREATEDOMAIN-1">
<refsect2info>
<date>2002-02-24</date>
</refsect2info>
<title>
Parameters
</title>
<para>
<variablelist>
<varlistentry>
<term><replaceable class="parameter">domainname</replaceable></term>
<listitem>
<para>
The name of a domain to be created.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><replaceable class="PARAMETER">data_type</replaceable></term>
<listitem>
<para>
The data type of the domain. This may include array specifiers.
Refer to the <citetitle>User's Guide</citetitle> for further
information about data types and arrays.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>DEFAULT
<replaceable>default_expr</replaceable></literal></term>
<listitem>
<para>
The <literal>DEFAULT</> clause assigns a default data value for
the column whose column definition it appears within. The value
is any variable-free expression (subselects and cross-references
to other columns in the current table are not allowed). The
data type of the default expression must match the data type of the
domain.
</para>
<para>
The default expression will be used in any insert operation that
does not specify a value for the domain. If there is no default
for a domain, then the default is NULL.
</para>
<note>
<para>
The default of a column will be tested before that of the domain.
</para>
</note>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>CONSTRAINT <replaceable class="PARAMETER">constraint_name</replaceable></literal></term>
<listitem>
<para>
An optional name for a domain. If not specified,
the system generates a name.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>NOT NULL</></term>
<listitem>
<para>
The column is not allowed to contain NULL values. This is
equivalent to the column constraint <literal>CHECK (<replaceable
class="PARAMETER">column</replaceable> NOT NULL)</literal>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>NULL</></term>
<listitem>
<para>
The column is allowed to contain NULL values. This is the default.
</para>
<para>
This clause is only available for compatibility with
non-standard SQL databases. Its use is discouraged in new
applications.
</para>
</listitem>
</varlistentry>
</variablelist>
</para>
</refsect2>
<refsect2 id="R2-SQL-CREATEDOMAIN-2">
<refsect2info>
<date>2002-02-24</date>
</refsect2info>
<title>
Outputs
</title>
<para>
<variablelist>
<varlistentry>
<term><computeroutput>
CREATE DOMAIN
</computeroutput></term>
<listitem>
<para>
Message returned if the domain is successfully created.
</para>
</listitem>
</varlistentry>
</variablelist>
</para>
</refsect2>
</refsynopsisdiv>
<refsect1 id="R1-SQL-CREATEDOMAIN-1">
<refsect1info>
<date>2002-02-24</date>
</refsect1info>
<title>
Description
</title>
<para>
<command>CREATE DOMAIN</command> allows the user to register a new user data
domain with PostgreSQL for use in the current data base. The
user who defines a domain becomes its owner.
<replaceable class="parameter">domainname</replaceable> is
the name of the new type and must be unique within the
types and domains defined for this database.
</para>
<para>
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 tables constraints individually.
</para>
</refsect1>
<refsect1>
<title>Examples</title>
<para>
This example creates the <type>country_code</type> data type and then uses the
type in a table definition:
<programlisting>
CREATE DOMAIN country_code char(2) NOT NULL;
CREATE TABLE countrylist (id INT4, country country_code);
</programlisting>
</para>
</refsect1>
<refsect1 id="SQL-CREATEDOMAIN-compatibility">
<title>Compatibility</title>
<para>
This <command>CREATE DOMAIN</command> command is a
<productname>PostgreSQL</productname> extension. CHECK and FOREIGN KEY
constraints are currently unsupported.
</para>
</refsect1>
<refsect1 id="SQL-CREATEDOMAIN-see-also">
<title>See Also</title>
<simplelist type="inline">
<member><xref linkend="sql-dropdomain"></member>
<member><citetitle>PostgreSQL Programmer's Guide</citetitle></member>
</simplelist>
</refsect1>
</refentry>
<!-- Keep this comment at the end of the file
Local variables:
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