title: Find the max value in a column of app engine datastore
body: <p>I have a table in google app engine datastore as <code>ItemData</code>with columns as below.</p>
  <blockquote>
  <p>item_no, letter, f_no, s_no, t_no</p>
  </blockquote>
  <p>I need to get the max value in <code>item_no</code> column.</p>
  <p>How can I achieve this?</p>