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<!--
$Header: /cvsroot/pgsql/doc/src/sgml/ref/alter_domain.sgml,v 1.5 2002/12/06 05:07:16 momjian Exp $
PostgreSQL documentation
-->
<refentry id="SQL-ALTERDOMAIN">
<refmeta>
<refentrytitle id="sql-alterdomain-title">ALTER DOMAIN</refentrytitle>
<refmiscinfo>SQL - Language Statements</refmiscinfo>
</refmeta>
<refnamediv>
<refname>
ALTER DOMAIN
</refname>
<refpurpose>
change the definition of a domain
</refpurpose>
</refnamediv>
<refsynopsisdiv>
<refsynopsisdivinfo>
<date>2002-11-27</date>
</refsynopsisdivinfo>
<synopsis>
ALTER DOMAIN <replaceable class="PARAMETER">domain</replaceable>
{ SET DEFAULT <replaceable class="PARAMETER">value</replaceable> | DROP DEFAULT }
ALTER DOMAIN <replaceable class="PARAMETER">domain</replaceable>
{ SET | DROP } NOT NULL
ALTER DOMAIN <replaceable class="PARAMETER">domain</replaceable>
ADD <replaceable class="PARAMETER">domain_constraint</replaceable>
ALTER DOMAIN <replaceable class="PARAMETER">domain</replaceable>
DROP CONSTRAINT <replaceable class="PARAMETER">constraint_name</replaceable> [ RESTRICT | CASCADE ]
</synopsis>
<refsect2 id="R2-SQL-ALTERDOMAIN-1">
<refsect2info>
<date>2002-11-27</date>
</refsect2info>
<title>
Inputs
</title>
<para>
<variablelist>
<varlistentry>
<term><replaceable class="PARAMETER"> domain </replaceable></term>
<listitem>
<para>
The name (possibly schema-qualified) of an existing domain to
alter.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><replaceable class="PARAMETER"> domain_constraint </replaceable></term>
<listitem>
<para>
New domain constraint for the domain.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><replaceable class="PARAMETER"> constraint_name </replaceable></term>
<listitem>
<para>
Name of an existing constraint to drop.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>CASCADE</term>
<listitem>
<para>
Automatically drop objects that depend constraint.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>RESTRICT</term>
<listitem>
<para>
Refuse to drop the constraint if there are any dependent
objects. This is the default behavior.
</para>
</listitem>
</varlistentry>
</variablelist>
</para>
</refsect2>
<refsect2 id="R2-SQL-ALTERDOMAIN-2">
<refsect2info>
<date>1998-04-15</date>
</refsect2info>
<title>
Outputs
</title>
<para>
<variablelist>
<varlistentry>
<term><computeroutput>ALTER DOMAIN</computeroutput></term>
<listitem>
<para>
Message returned from domain alteration.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><computeroutput>ERROR</computeroutput></term>
<listitem>
<para>
Message returned if domain is not available.
</para>
</listitem>
</varlistentry>
</variablelist>
</para>
</refsect2>
</refsynopsisdiv>
<refsect1 id="R1-SQL-ALTERDOMAIN-1">
<refsect1info>
<date>2002-11-27</date>
</refsect1info>
<title>
Description
</title>
<para>
<command>ALTER DOMAIN</command> changes the definition of an existing domain.
There are several sub-forms:
</para>
<variablelist>
<varlistentry>
<term>SET/DROP DEFAULT</term>
<listitem>
<para>
These forms set or remove the default value for a column. Note
that defaults only apply to subsequent <command>INSERT</command>
commands; they do not cause rows already in a table using the domain.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>SET/DROP NOT NULL</term>
<listitem>
<para>
These forms change whether a domain is marked to allow NULL
values or to reject NULL values. You may only <literal>SET NOT NULL</>
when the tables using the domain contain no null values in the domain
based column.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>ADD <replaceable class="PARAMETER">domain_constraint</replaceable></term>
<listitem>
<para>
This form adds a new constraint to a table using the same syntax as
<xref linkend="SQL-CREATEDOMAIN" endterm="SQL-CREATEDOMAIN-TITLE">.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>DROP CONSTRAINT</term>
<listitem>
<para>
This form drops constraints on a domain.
</para>
</listitem>
</varlistentry>
</variablelist>
<para>
You must own the domain to use <command>ALTER DOMAIN</>; except for
<command>ALTER TABLE OWNER</>, which may only be executed by a superuser.
</para>
</refsect1>
<refsect1 id="R1-SQL-ALTERDOMAIN-2">
<title>
Usage
</title>
<para>
To add a NOT NULL constraint to a column:
<programlisting>
ALTER DOMAIN zipcode SET NOT NULL;
</programlisting>
To remove a NOT NULL constraint from a column:
<programlisting>
ALTER DOMAIN zipcode DROP NOT NULL;
</programlisting>
</para>
<para>
To add a check constraint to a table:
<programlisting>
ALTER DOMAIN zipcode ADD CONSTRAINT zipchk CHECK (char_length(VALUE) = 5);
</programlisting>
</para>
<para>
To remove a check constraint from a table and all its children:
<programlisting>
ALTER DOMAIN zipcode DROP CONSTRAINT zipchk;
</programlisting>
</para>
</refsect1>
</refentry>
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