<!--
doc/src/sgml/ref/alter_index.sgml
PostgreSQL documentation
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<refentry id="SQL-ALTERINDEX">
 <refmeta>
  <refentrytitle>ALTER INDEX</refentrytitle>
  <manvolnum>7</manvolnum>
  <refmiscinfo>SQL - Language Statements</refmiscinfo>
 </refmeta>

 <refnamediv>
  <refname>ALTER INDEX</refname>
  <refpurpose>change the definition of an index</refpurpose>
 </refnamediv>

 <indexterm zone="sql-alterindex">
  <primary>ALTER INDEX</primary>
 </indexterm>

 <refsynopsisdiv>
<synopsis>
ALTER INDEX [ IF EXISTS ] <replaceable class="PARAMETER">name</replaceable> RENAME TO <replaceable class="PARAMETER">new_name</replaceable>
ALTER INDEX [ IF EXISTS ] <replaceable class="PARAMETER">name</replaceable> SET TABLESPACE <replaceable class="PARAMETER">tablespace_name</replaceable>
ALTER INDEX [ IF EXISTS ] <replaceable class="PARAMETER">name</replaceable> SET ( <replaceable class="PARAMETER">storage_parameter</replaceable> = <replaceable class="PARAMETER">value</replaceable> [, ... ] )
ALTER INDEX [ IF EXISTS ] <replaceable class="PARAMETER">name</replaceable> RESET ( <replaceable class="PARAMETER">storage_parameter</replaceable> [, ... ] )
</synopsis>
 </refsynopsisdiv>

 <refsect1>
  <title>Description</title>

  <para>
   <command>ALTER INDEX</command> changes the definition of an existing index.
   There are several subforms:

  <variablelist>

   <varlistentry>
    <term><literal>IF EXISTS</literal></term>
    <listitem>
     <para>
      Do not throw an error if the index does not exist. A notice is issued
      in this case.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><literal>RENAME</literal></term>
    <listitem>
     <para>
      The <literal>RENAME</literal> form changes the name of the index.
      There is no effect on the stored data.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><literal>SET TABLESPACE</literal></term>
    <listitem>
     <para>
      This form changes the index's tablespace to the specified tablespace and
      moves the data file(s) associated with the index to the new tablespace.
      See also
      <xref linkend="SQL-CREATETABLESPACE">.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><literal>SET ( <replaceable class="PARAMETER">storage_parameter</replaceable> = <replaceable class="PARAMETER">value</replaceable> [, ... ] )</literal></term>
    <listitem>
     <para>
      This form changes one or more index-method-specific storage parameters
      for the index.  See
      <xref linkend="SQL-CREATEINDEX">
      for details on the available parameters.  Note that the index contents
      will not be modified immediately by this command; depending on the
      parameter you might need to rebuild the index with
      <xref linkend="SQL-REINDEX">
      to get the desired effects.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><literal>RESET ( <replaceable class="PARAMETER">storage_parameter</replaceable> [, ... ] )</literal></term>
    <listitem>
     <para>
      This form resets one or more index-method-specific storage parameters to
      their defaults.  As with <literal>SET</>, a <literal>REINDEX</literal>
      might be needed to update the index entirely.
     </para>
    </listitem>
   </varlistentry>

  </variablelist>
  </para>

 </refsect1>

 <refsect1>
  <title>Parameters</title>

    <variablelist>

     <varlistentry>
      <term><replaceable class="PARAMETER">name</replaceable></term>
      <listitem>
       <para>
        The name (possibly schema-qualified) of an existing index to
        alter.
       </para>
      </listitem>
     </varlistentry>

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

     <varlistentry>
      <term><replaceable class="PARAMETER">tablespace_name</replaceable></term>
      <listitem>
       <para>
        The tablespace to which the index will be moved.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><replaceable class="PARAMETER">storage_parameter</replaceable></term>
      <listitem>
       <para>
        The name of an index-method-specific storage parameter.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><replaceable class="PARAMETER">value</replaceable></term>
      <listitem>
       <para>
        The new value for an index-method-specific storage parameter.
        This might be a number or a word depending on the parameter.
       </para>
      </listitem>
     </varlistentry>

    </variablelist>
 </refsect1>

 <refsect1>
  <title>Notes</title>

   <para>
    These operations are also possible using
    <xref linkend="SQL-ALTERTABLE">.
    <command>ALTER INDEX</> is in fact just an alias for the forms
    of <command>ALTER TABLE</> that apply to indexes.
   </para>

   <para>
    There was formerly an <command>ALTER INDEX OWNER</> variant, but
    this is now ignored (with a warning).  An index cannot have an owner
    different from its table's owner.  Changing the table's owner
    automatically changes the index as well.
   </para>

   <para>
    Changing any part of a system catalog index is not permitted.
   </para>
 </refsect1>

 <refsect1>
  <title>Examples</title>
  <para>
   To rename an existing index:
<programlisting>
ALTER INDEX distributors RENAME TO suppliers;
</programlisting>
  </para>

  <para>
   To move an index to a different tablespace:
<programlisting>
ALTER INDEX distributors SET TABLESPACE fasttablespace;
</programlisting>
  </para>

  <para>
   To change an index's fill factor (assuming that the index method
   supports it):
<programlisting>
ALTER INDEX distributors SET (fillfactor = 75);
REINDEX INDEX distributors;
</programlisting></para>

 </refsect1>

 <refsect1>
  <title>Compatibility</title>

  <para>
   <command>ALTER INDEX</> is a <productname>PostgreSQL</productname>
   extension.
  </para>
 </refsect1>


 <refsect1>
  <title>See Also</title>

  <simplelist type="inline">
   <member><xref linkend="sql-createindex"></member>
   <member><xref linkend="sql-reindex"></member>
  </simplelist>
 </refsect1>
</refentry>