title: ROW_NUMBER() with Qualify clause in Vertica
body: <pre><code>select a.pm_id, a.pm_name
  from loc_table a
  qualify row_number() over(partition by pm_id order by pm_name asc) =1;
  </code></pre>
  <p>Can we write it this way in Vertica, I tried it but the qualify keyword is not taken by Vertica and the from Clause has to be at the end.
  Can anybody explain what the above query does and how can we achieve the same in Vertica.</p>