title: concatenating multiple fields in one record sql
body: <p>I would like to to get the sum(gross) per month per each user AND show each event field. 
  So I would need to show these columns</p>
  
  <p>My table</p>
  
  <pre><code>  order id, user, month, event, gross
         1 jack october event2 30
         2 jack november event3 20
         3 jack november event3 20
         4 jack november event2 30
         5 sam november event2 30
         6 john october event3 20
  </code></pre>
  
  <p>For Jack the results would be</p>
  
  <pre><code>   record1
      user = jack
      month = november
      event = event2, event3
      total = 70
  
      record2
      user = jack
      month = october
      event = event3
      total = 30
  </code></pre>
  
  <p>So the solution I believe would be concatenating multiple event fields in one record. I have seen UNION do something like this creating comma separated values in one column but not sure how to use it here.</p>