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

<refentry id="SQL-REFRESHMATERIALIZEDVIEW">
 <indexterm zone="sql-refreshmaterializedview">
  <primary>REFRESH MATERIALIZED VIEW</primary>
 </indexterm>

 <refmeta>
  <refentrytitle>REFRESH MATERIALIZED VIEW</refentrytitle>
  <manvolnum>7</manvolnum>
  <refmiscinfo>SQL - Language Statements</refmiscinfo>
 </refmeta>

 <refnamediv>
  <refname>REFRESH MATERIALIZED VIEW</refname>
  <refpurpose>replace the contents of a materialized view</refpurpose>
 </refnamediv>

 <refsynopsisdiv>
<synopsis>
REFRESH MATERIALIZED VIEW [ CONCURRENTLY ] <replaceable class="PARAMETER">name</replaceable>
    [ WITH [ NO ] DATA ]
</synopsis>
 </refsynopsisdiv>

 <refsect1>
  <title>Description</title>

  <para>
   <command>REFRESH MATERIALIZED VIEW</command> completely replaces the
   contents of a materialized view.  The old contents are discarded.  If
   <literal>WITH DATA</literal> is specified (or defaults) the backing query
   is executed to provide the new data, and the materialized view is left in a
   scannable state.  If <literal>WITH NO DATA</literal> is specified no new
   data is generated and the materialized view is left in an unscannable
   state.
  </para>
  <para>
   <literal>CONCURRENTLY</literal> and <literal>WITH NO DATA</literal> may not
   be specified together.
  </para>
 </refsect1>

 <refsect1>
  <title>Parameters</title>

  <variablelist>
   <varlistentry>
    <term><literal>CONCURRENTLY</literal></term>
    <listitem>
     <para>
      Refresh the materialized view without locking out concurrent selects on
      the materialized view.  Without this option a refresh which affects a
      lot of rows will tend to use fewer resources and complete more quickly,
      but could block other connections which are trying to read from the
      materialized view.  This option may be faster in cases where a small
      number of rows are affected.
     </para>
     <para>
      This option is only allowed if there is at least one
      <literal>UNIQUE</literal> index on the materialized view which uses only
      column names and includes all rows; that is, it must not index on any
      expressions nor include a <literal>WHERE</literal> clause.
     </para>
     <para>
      This option may not be used when the materialized view is not already
      populated.
     </para>
     <para>
      Even with this option only one <literal>REFRESH</literal> at a time may
      run against any one materialized view.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><replaceable class="PARAMETER">name</replaceable></term>
    <listitem>
     <para>
      The name (optionally schema-qualified) of the materialized view to
      refresh.
     </para>
    </listitem>
   </varlistentry>
  </variablelist>
 </refsect1>

 <refsect1>
  <title>Notes</title>

  <para>
   While the default index for future
   <xref linkend="SQL-CLUSTER">
   operations is retained, <command>REFRESH MATERIALIZED VIEW</> does not
   order the generated rows based on this property. If you want the data
   to be ordered upon generation, you must use an <literal>ORDER BY</>
   clause in the backing query.
  </para>
 </refsect1>

 <refsect1>
  <title>Examples</title>

  <para>
   This command will replace the contents of the materialized view called
   <literal>order_summary</literal> using the query from the materialized
   view's definition, and leave it in a scannable state:
<programlisting>
REFRESH MATERIALIZED VIEW order_summary;
</programlisting>
  </para>

  <para>
   This command will free storage associated with the materialized view
   <literal>annual_statistics_basis</literal> and leave it in an unscannable
   state:
<programlisting>
REFRESH MATERIALIZED VIEW annual_statistics_basis WITH NO DATA;
</programlisting></para>
 </refsect1>

 <refsect1>
  <title>Compatibility</title>

  <para>
   <command>REFRESH MATERIALIZED VIEW</command> is a
   <productname>PostgreSQL</productname> extension.
  </para>
 </refsect1>

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

  <simplelist type="inline">
   <member><xref linkend="sql-creatematerializedview"></member>
   <member><xref linkend="sql-altermaterializedview"></member>
   <member><xref linkend="sql-dropmaterializedview"></member>
  </simplelist>
 </refsect1>

</refentry>
