estimated number of rows that the planner
       should expect the function to return.  This is only allowed when the
       function is declared to return a set.  The default assumption is
       1000 rows.
      </para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term><literal>SUPPORT</literal> <replaceable class="parameter">support_function</replaceable></term>

     <listitem>
      <para>
       The name (optionally schema-qualified) of a <firstterm>planner support
       function</firstterm> to use for this function.  See
       <xref linkend="xfunc-optimization"/> for details.
       You must be superuser to use this option.
      </para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term><replaceable>configuration_parameter</replaceable></term>
     <term><replaceable>value</replaceable></term>
     <listitem>
      <para>
       The <literal>SET</literal> clause causes the specified configuration
       parameter to be set to the specified value when the function is
       entered, and then restored to its prior value when the function exits.
       <literal>SET FROM CURRENT</literal> saves the value of the parameter that
       is current when <command>CREATE FUNCTION</command> is executed as the value
       to be applied when the function is entered.
      </para>

      <para>
       If a <literal>SET</literal> clause is attached to a function, then
       the effects of a <command>SET LOCAL</command> command executed inside the
       function for the same variable are restricted to the function: the
       configuration parameter's prior value is still restored at function exit.
       However, an ordinary
       <command>SET</command> command (without <literal>LOCAL</literal>) overrides the
       <literal>SET</literal> clause, much as it would do for a previous <command>SET
       LOCAL</command> command: the effects of such a command will persist after
       function exit, unless the current transaction is rolled back.
      </para>

      <para>
       See <xref linkend="sql-set"/> and
       <xref linkend="runtime-config"/>
       for more information about allowed parameter names and values.
      </para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term><replaceable class="parameter">definition</replaceable></term>

     <listitem>
      <para>
       A string constant defining the function; the meaning depends on the
       language.  It can be an internal function name, the path to an
       object file, an SQL command, or text in a procedural language.
      </para>

      <para>
       It is often helpful to use dollar quoting (see <xref
       linkend="sql-syntax-dollar-quoting"/>) to write the function definition
       string, rather than the normal single quote syntax.  Without dollar
       quoting, any single quotes or backslashes in the function definition must
       be escaped by doubling them.
      </para>

     </listitem>
    </varlistentry>

    <varlistentry>
     <term><literal><replaceable class="parameter">obj_file</replaceable>, <replaceable class="parameter">link_symbol</replaceable></literal></term>

     <listitem>
      <para>
       This form of the <literal>AS</literal> clause is used for
       dynamically loadable C language functions when the function name
       in the C language source code is not the same as the name of
       the SQL function. The string <replaceable
       class="parameter">obj_file</replaceable> is the name of the shared
       library file containing the compiled C function, and is interpreted
       as for the <link linkend="sql-load"><command>LOAD</command></link> command.  The string
       <replaceable class="parameter">link_symbol</replaceable> is the
       function's link symbol, that is, the name of the function in the C
       language source code.  If the link symbol is omitted, it is assumed to
       be the same as the name of the SQL function being defined.  The C names
       of all