title: how do i get last result in group by MySQL query (not the first)
body: <p>I have the following table:</p>
  
  <pre>
  +--+-------------------+---------------------+-----------------------+
  |ID| lt_user           | lt_time_stamp       | lt_activity_operation |
  +--+-------------------+---------------------+-----------------------+
  |1 | External Sales    | 2013-02-15 15:17:34 | login                 |
  |2 | External Sales    | 2013-03-20 16:25:09 | login                 |
  |3 | Internal Sales    | 2013-07-29 13:09:22 | login                 |
  |4 | Internal Sales    | 2013-08-01 11:06:11 | login                 |
  |5 | Internal sales    | 2013-08-02 10:06:59 | login                 |
  |6 | internal sales    | 2013-08-02 10:21:38 | login                 |
  |7 | internal sales    | 2013-08-07 16:13:01 | login                 |
  |8 | Internal Sales    | 2013-08-12 10:51:16 | login                 |
  +--+-------------------+---------------------+-----------------------+
  </pre>
  
  <p>I'm trying to retrieve the last instance (Time stamp) of each user once.</p>
  
  <p>What i need is: </p>
  
  <pre>
  +--+-------------------+---------------------+-----------------------+
  |ID| lt_user           | lt_time_stamp       | lt_activity_operation |
  +--+-------------------+---------------------+-----------------------+
  |2 | External Sales    | 2013-03-20 16:25:09 | login                 |
  |8 | Internal Sales    | 2013-08-12 10:51:16 | login                 |
  +--+-------------------+---------------------+-----------------------+
  </pre>
  
  <p>What I'm getting is:</p>
  
  <pre>
  +--+-------------------+---------------------+-----------------------+
  |ID| lt_user           | lt_time_stamp       | lt_activity_operation |
  +--+-------------------+---------------------+-----------------------+
  |3 | Internal Sales    | 2013-07-29 13:09:22 | login                 |
  |1 | External Sales    | 2013-02-15 15:17:34 | login                 |
  +--+-------------------+---------------------+-----------------------+
  </pre>
  
  <p>My Query is:</p>
  
  <pre><code>SELECT lt_user, lt_time_stamp, lt_activity_operation
    FROM log_table
   GROUP BY lt_user
   ORDER BY lt_time_stamp DESC;
  </code></pre>
  
  <p>Thanks</p>