<application>PL/SQL</application> version, but you have to remember to use
     <function>quote_literal</function> and
     <function>quote_ident</function> as described in <xref
     linkend="plpgsql-statements-executing-dyn"/>.  Constructs of the
     type <literal>EXECUTE 'SELECT * FROM $1';</literal> will not work
     reliably unless you use these functions.
    </para>
   </sect3>

   <sect3 id="plpgsql-porting-optimization">
    <title>Optimizing <application>PL/pgSQL</application> Functions</title>

    <para>
     <productname>PostgreSQL</productname> gives you two function creation
     modifiers to optimize execution: <quote>volatility</quote> (whether
     the function always returns the same result when given the same
     arguments) and <quote>strictness</quote> (whether the function
     returns null if any argument is null).  Consult the <xref
     linkend="sql-createfunction"/>
     reference page for details.
    </para>

    <para>
     When making use of these optimization attributes, your
     <command>CREATE FUNCTION</command> statement might look something
     like this:

<programlisting>
CREATE FUNCTION foo(...) RETURNS integer AS $$
...
$$ LANGUAGE plpgsql STRICT IMMUTABLE;
</programlisting>
    </para>
   </sect3>
  </sect2>

  <sect2 id="plpgsql-porting-appendix">
   <title>Appendix</title>

   <para>
    This section contains the code for a set of Oracle-compatible
    <function>instr</function> functions that you can use to simplify
    your porting efforts.
   </para>

   <indexterm>
    <primary><function>instr</function> function</primary>
   </indexterm>

<programlisting><![CDATA[
--
-- instr functions that mimic Oracle's counterpart
-- Syntax: instr(string1, string2 [, n [, m]])
-- where [] denotes optional parameters.
--
-- Search string1, beginning at the nth character, for the mth occurrence
-- of string2.  If n is negative, search backwards, starting at the abs(n)'th
-- character from the end of string1.
-- If n is not passed, assume 1 (search starts at first character).
-- If m is not passed, assume 1 (find first occurrence).
-- Returns starting index of string2 in string1, or 0 if string2 is not found.
--

CREATE FUNCTION instr(varchar, varchar) RETURNS integer AS $$
BEGIN
    RETURN instr($1, $2, 1);
END;
$$ LANGUAGE plpgsql STRICT IMMUTABLE;


CREATE FUNCTION instr(string varchar, string_to_search_for varchar,
                      beg_index integer)
RETURNS