postgresql/doc/src/sgml/ref/call.sgml

<!--
doc/src/sgml/ref/call.sgml
PostgreSQL documentation
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<refentry id="sql-call">
 <indexterm zone="sql-call">
  <primary>CALL</primary>
 </indexterm>

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

 <refnamediv>
  <refname>CALL</refname>
  <refpurpose>invoke a procedure</refpurpose>
 </refnamediv>

 <refsynopsisdiv>
<synopsis>
CALL <replaceable class="parameter">name</replaceable> ( [ <replaceable class="parameter">argument</replaceable> ] [, ...] )
</synopsis>
 </refsynopsisdiv>

 <refsect1>
  <title>Description</title>

  <para>
   <command>CALL</command> executes a procedure.
  </para>

  <para>
   If the procedure has any output parameters, then a result row will be
   returned, containing the values of those parameters.
  </para>
 </refsect1>

 <refsect1>
  <title>Parameters</title>

  <variablelist>
   <varlistentry>
    <term><replaceable class="parameter">name</replaceable></term>
    <listitem>
     <para>
      The name (optionally schema-qualified) of the procedure.
     </para>
    </listitem>
   </varlistentry>

  <varlistentry>
    <term><replaceable class="parameter">argument</replaceable></term>
    <listitem>
     <para>
      An argument expression for the procedure call.
     </para>

     <para>
      Arguments can include parameter names, using the syntax
      <literal><replaceable class="parameter">name</replaceable> =&gt; <replaceable class="parameter">value</replaceable></literal>.
      This works the same as in ordinary function calls; see
      <xref linkend="sql-syntax-calling-funcs"/> for details.
     </para>

     <para>
      Arguments must be supplied for all procedure parameters that lack
      defaults, including <literal>OUT</literal> parameters.  However,
      arguments matching <literal>OUT</literal> parameters are not evaluated,
      so it's customary to just write <literal>NULL</literal> for them.
      (Writing something else for an <literal>OUT</literal> parameter
      might cause compatibility problems with
      future <productname>PostgreSQL</productname> versions.)
     </para>
    </listitem>
   </varlistentry>
  </variablelist>
 </refsect1>

 <refsect1>
  <title>Notes</title>

  <para>
   The user must have <literal>EXECUTE</literal> privilege on the procedure in
   order to be allowed to invoke it.
  </para>

  <para>
   To call a function (not a procedure), use <command>SELECT</command> instead.
  </para>

  <para>
   If <command>CALL</command> is executed in a transaction block, then the
   called procedure cannot execute transaction control statements.
   Transaction control statements are only allowed if <command>CALL</command>
   is executed in its own transaction.
  </para>

  <para>
   <application>PL/pgSQL</application> handles output parameters
   in <command>CALL</command> commands differently;
   see <xref linkend="plpgsql-statements-calling-procedure"/>.
  </para>
 </refsect1>

 <refsect1>
  <title>Examples</title>
<programlisting>
CALL do_db_maintenance();
</programlisting>
 </refsect1>

 <refsect1>
  <title>Compatibility</title>

  <para>
   <command>CALL</command> conforms to the SQL standard,
   except for the handling of output parameters.  The standard
   says that users should write variables to receive the values
   of output parameters.
  </para>
 </refsect1>

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

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