function call in the arguments of a window function,
    but not vice versa.
   </p><p>
    If there is a need to filter or group rows after the window calculations
    are performed, you can use a sub-select.  For example:

</p><pre class="programlisting">
SELECT depname, empno, salary, enroll_date
FROM
  (SELECT depname, empno, salary, enroll_date,
          rank() OVER (PARTITION BY depname ORDER BY salary DESC, empno) AS pos
     FROM empsalary
  ) AS ss
WHERE pos &lt; 3;
</pre><p>

    The above query 