<!--
doc/src/sgml/ref/alter_domain.sgml
PostgreSQL documentation
-->

<refentry id="sql-alterdomain">
 <indexterm zone="sql-alterdomain">
  <primary>ALTER DOMAIN</primary>
 </indexterm>

 <refmeta>
  <refentrytitle>ALTER DOMAIN</refentrytitle>
  <manvolnum>7</manvolnum>
  <refmiscinfo>SQL - Language Statements</refmiscinfo>
 </refmeta>

 <refnamediv>
  <refname>ALTER DOMAIN</refname>
  <refpurpose>
   change the definition of a domain
  </refpurpose>
 </refnamediv>

 <refsynopsisdiv>
<synopsis>
ALTER DOMAIN <replaceable class="parameter">name</replaceable>
    { SET DEFAULT <replaceable class="parameter">expression</replaceable> | DROP DEFAULT }
ALTER DOMAIN <replaceable class="parameter">name</replaceable>
    { SET | DROP } NOT NULL
ALTER DOMAIN <replaceable class="parameter">name</replaceable>
    ADD <replaceable class="parameter">domain_constraint</replaceable> [ NOT VALID ]
ALTER DOMAIN <replaceable class="parameter">name</replaceable>
    DROP CONSTRAINT [ IF EXISTS ] <replaceable class="parameter">constraint_name</replaceable> [ RESTRICT | CASCADE ]
ALTER DOMAIN <replaceable class="parameter">name</replaceable>
     RENAME CONSTRAINT <replaceable class="parameter">constraint_name</replaceable> TO <replaceable class="parameter">new_constraint_name</replaceable>
ALTER DOMAIN <replaceable class="parameter">name</replaceable>
    VALIDATE CONSTRAINT <replaceable class="parameter">constraint_name</replaceable>
ALTER DOMAIN <replaceable class="parameter">name</replaceable>
    OWNER TO { <replaceable class="parameter">new_owner</replaceable> | CURRENT_USER | SESSION_USER }
ALTER DOMAIN <replaceable class="parameter">name</replaceable>
    RENAME TO <replaceable class="parameter">new_name</replaceable>
ALTER DOMAIN <replaceable class="parameter">name</replaceable>
    SET SCHEMA <replaceable class="parameter">new_schema</replaceable>
</synopsis>
 </refsynopsisdiv>

 <refsect1>
  <title>Description</title>

  <para>
   <command>ALTER DOMAIN</command> changes the definition of an existing domain.
   There are several sub-forms:
  </para>

  <variablelist>
   <varlistentry>
    <term><literal>SET</literal>/<literal>DROP DEFAULT</literal></term>
    <listitem>
     <para>
      These forms set or remove the default value for a domain. Note
      that defaults only apply to subsequent <command>INSERT</command>
      commands; they do not affect rows already in a table using the domain.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><literal>SET</literal>/<literal>DROP NOT NULL</literal></term>
    <listitem>
     <para>
      These forms change whether a domain is marked to allow NULL
      values or to reject NULL values.  You can only <literal>SET NOT NULL</literal>
      when the columns using the domain contain no null values.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><literal>ADD <replaceable class="parameter">domain_constraint</replaceable> [ NOT VALID ]</literal></term>
    <listitem>
     <para>
      This form adds a new constraint to a domain using the same syntax as
      <xref linkend="sql-createdomain"/>.
      When a new constraint is added to a domain, all columns using that
      domain will be checked against the newly added constraint.  These
      checks can be suppressed by adding the new constraint using the
      <literal>NOT VALID</literal> option; the constraint can later be made
      valid using <command>ALTER DOMAIN ... VALIDATE CONSTRAINT</command>.
      Newly inserted or updated rows are always checked against all
      constraints, even those marked <literal>NOT VALID</literal>.
      <literal>NOT VALID</literal> is only accepted for <literal>CHECK</literal> constraints.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><literal>DROP CONSTRAINT [ IF EXISTS ]</literal></term>
    <listitem>
     <para>
      This form drops constraints on a domain.
      If <literal>IF EXISTS</literal> is specified and the constraint
      does not exist, no error is thrown. In this case a notice is issued instead.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><literal>RENAME CONSTRAINT</literal></term>
    <listitem>
     <para>
      This form changes the name of a constraint on a domain.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><literal>VALIDATE CONSTRAINT</literal></term>
    <listitem>
     <para>
      This form validates a constraint previously added as
      <literal>NOT VALID</literal>, that is, it verifies that all values in
      table columns of the domain type satisfy the specified constraint.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><literal>OWNER</literal></term>
    <listitem>
     <para>
      This form changes the owner of the domain to the specified user.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><literal>RENAME</literal></term>
    <listitem>
     <para>
      This form changes the name of the domain.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><literal>SET SCHEMA</literal></term>
    <listitem>
     <para>
      This form changes the schema of the domain.  Any constraints
      associated with the domain are moved into the new schema as well.
     </para>
    </listitem>
   </varlistentry>
  </variablelist>

  <para>
   You must own the domain to use <command>ALTER DOMAIN</command>.
   To change the schema of a domain, you must also have
   <literal>CREATE</literal> privilege on the new schema.
   To alter the owner, you must also be a direct or indirect member of the new
   owning role, and that role must have <literal>CREATE</literal> privilege on
   the domain's schema.  (These restrictions enforce that altering the owner
   doesn't do anything you couldn't do by dropping and recreating the domain.
   However, a superuser can alter ownership of any domain anyway.)
  </para>
 </refsect1>

 <refsect1>
  <title>Parameters</title>

   <para>
    <variablelist>
     <varlistentry>
      <term><replaceable class="parameter">name</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 or rename.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><literal>NOT VALID</literal></term>
      <listitem>
       <para>
        Do not verify existing stored data for constraint validity.
       </para>
      </listitem>
     </varlistentry>


     <varlistentry>
      <term><literal>CASCADE</literal></term>
      <listitem>
       <para>
        Automatically drop objects that depend on the constraint,
        and in turn all objects that depend on those objects
        (see <xref linkend="ddl-depend"/>).
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><literal>RESTRICT</literal></term>
      <listitem>
       <para>
        Refuse to drop the constraint if there are any dependent
        objects. This is the default behavior.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><replaceable class="parameter">new_name</replaceable></term>
      <listitem>
       <para>
        The new name for the domain.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><replaceable class="parameter">new_constraint_name</replaceable></term>
      <listitem>
       <para>
        The new name for the constraint.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><replaceable class="parameter">new_owner</replaceable></term>
      <listitem>
       <para>
        The user name of the new owner of the domain.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><replaceable class="parameter">new_schema</replaceable></term>
      <listitem>
       <para>
        The new schema for the domain.
       </para>
      </listitem>
     </varlistentry>

    </variablelist>
   </para>
  </refsect1>

 <refsect1>
  <title>Notes</title>

  <para>
   Although <command>ALTER DOMAIN ADD CONSTRAINT</command> attempts to verify
   that existing stored data satisfies the new constraint, this check is not
   bulletproof, because the command cannot <quote>see</quote> table rows that
   are newly inserted or updated and not yet committed.  If there is a hazard
   that concurrent operations might insert bad data, the way to proceed is to
   add the constraint using the <literal>NOT VALID</literal> option, commit
   that command, wait until all transactions started before that commit have
   finished, and then issue <command>ALTER DOMAIN VALIDATE
   CONSTRAINT</command> to search for data violating the constraint.  This
   method is reliable because once the constraint is committed, all new
   transactions are guaranteed to enforce it against new values of the domain
   type.
  </para>

  <para>
   Currently, <command>ALTER DOMAIN ADD CONSTRAINT</command>, <command>ALTER
   DOMAIN VALIDATE CONSTRAINT</command>, and <command>ALTER DOMAIN SET NOT
   NULL</command> will fail if the named domain or any derived domain is used
   within a container-type column (a composite, array, or range column) in
   any table in the database.  They should eventually be improved to be able
   to verify the new constraint for such nested values.
  </para>

 </refsect1>

 <refsect1>
  <title>Examples</title>

  <para>
   To add a <literal>NOT NULL</literal> constraint to a domain:
<programlisting>
ALTER DOMAIN zipcode SET NOT NULL;
</programlisting>
   To remove a <literal>NOT NULL</literal> constraint from a domain:
<programlisting>
ALTER DOMAIN zipcode DROP NOT NULL;
</programlisting>
  </para>

  <para>
   To add a check constraint to a domain:
<programlisting>
ALTER DOMAIN zipcode ADD CONSTRAINT zipchk CHECK (char_length(VALUE) = 5);
</programlisting>
  </para>

  <para>
   To remove a check constraint from a domain:
<programlisting>
ALTER DOMAIN zipcode DROP CONSTRAINT zipchk;
</programlisting>
  </para>

  <para>
   To rename a check constraint on a domain:
<programlisting>
ALTER DOMAIN zipcode RENAME CONSTRAINT zipchk TO zip_check;
</programlisting>
  </para>

  <para>
   To move the domain into a different schema:
<programlisting>
ALTER DOMAIN zipcode SET SCHEMA customers;
</programlisting></para>
 </refsect1>

 <refsect1 id="sql-alterdomain-compatibility">
  <title>Compatibility</title>

  <para>
   <command>ALTER DOMAIN</command> conforms to the <acronym>SQL</acronym>
   standard, except for the <literal>OWNER</literal>, <literal>RENAME</literal>, <literal>SET SCHEMA</literal>, and
   <literal>VALIDATE CONSTRAINT</literal> variants, which are
   <productname>PostgreSQL</productname> extensions.  The <literal>NOT VALID</literal>
   clause of the <literal>ADD CONSTRAINT</literal> variant is also a
   <productname>PostgreSQL</productname> extension.
  </para>
 </refsect1>

 <refsect1 id="sql-alterdomain-see-also">
  <title>See Also</title>

  <simplelist type="inline">
   <member><xref linkend="sql-createdomain"/></member>
   <member><xref linkend="sql-dropdomain"/></member>
  </simplelist>
 </refsect1>

</refentry>
