title: date addition when difference is column data
body: <p>how to add when add data is given in another column. Also the duration is months.</p>
  
  <pre><code>DOJ     DURATION
  --------- ----------
  25-MAY-11      6
  06-JUN-11      3
  25-MAY-11      6
  18-APR-11      2
  10-MAR-11      2
  18-APR-11      2
  10-MAR-11      2
  18-APR-11      2
  10-MAR-11      2
  06-JUN-11      3
  10-MAR-11      4
  </code></pre>
  
  <p>out put should be date plus months
  error is unidentified identifier:dateadd</p>