title: Prepare data at ID,Month level in SQL
body: <p>I have a table that is something like this:</p>
  
  <pre><code>ID  Date
  1   10/04/2015
  1   28/04/2015
  1   14/07/2015
  1   30/07/2015
  1   30/08/2015
  2   10/04/2016
  2   28/04/2016
  2   14/05/2016
  2   30/05/2016
  </code></pre>
  
  <p>but i am trying to achieve like:</p>
  
  <pre><code>ID  Date
  1   28/04/2015
  1   30/07/2015
  1   30/08/2015
  2   28/04/2016
  2   30/05/2016
  </code></pre>
  
  <p>Could you please help me . </p>