title: Return one record per month
body: <p>I haven't figured out how to group by date to get one 1 record per month this is my query:</p>
  
  <pre><code>select Date, weight 
    from Usrs 
   where usr = b 
   order by month
  </code></pre>
  
  <p>Which returns:</p>
  
  <pre><code>user b
  date        weight
  15/03/2017  18
  15/03/2017  14
  19/02/2017  19
  18/03/2017  9
  22/04/2017  24
  30/04/2017  33
  01/05/2017  15
  03/05/2017  30
  </code></pre>
  
  <p>but I only need the last record of each month so what I want it will be like this</p>
  
  <pre><code>date        weight
  15/03/2017  18
  19/02/2017  19
  18/03/2017  9
  30/04/2017  33
  03/05/2017  30
  </code></pre>
  
  <p>Any ideas how could I achieve my goal?</p>