title: Select only maximum value record for multiple rows
body: <p>I have one table, which having records like</p>
  
  <pre><code>Unit    Rate    Date-effected
  -------------------------------------------
  ALHA    ILS     2014-03-02 00:00:00.000
  ALHA    ILS     2014-08-02 00:00:00.000
  BUCK    ILS     2013-02-14 00:00:00.000
  BUCK    ILS     2014-03-02 00:00:00.000
  BUCK    ILS     2014-08-02 00:00:00.000
  CASC    ILD     2013-02-14 00:00:00.000
  CASC    ILD     2014-03-02 00:00:00.000
  CASC    ILD     2014-08-02 00:00:00.000   
  </code></pre>
  
  <p>now, I want only maximum date value record selection in result <code>table</code>. which is,</p>
  
  <pre><code>Unit    Rate    DateEffected
  -------------------------------------------
  ALHA    ILS     2014-08-02 00:00:00.000
  BUCK    ILS     2014-08-02 00:00:00.000
  CASC    ILD     2014-08-02 00:00:00.000   
  </code></pre>