title: Problem with a SQL SELECT Query
body: <p>I have a table GAMES with this information:</p>
  
  <pre><code>- Id_Game (int)
  - Id_Referee1 (int)
  - Id_Referee2 (int)
  </code></pre>
  
  <p>These are some rows:</p>
  
  <pre><code>ID_GAME    ID_REFEREE1    ID_REFEREE2
  1          1000           728
  2          1004           813
  3          728            1004
  4          1004           1000
  </code></pre>
  
  <p>I want to have a list with the number of games that a referee has officiated, doesn't matter if as a Referee1 or Referee2. In this case, I would like to receive this list order by number of games DESC.</p>
  
  <pre><code>REFEREE    NUMBER OF GAMES
  1004       3
  728        2
  1000       2
  813        1
  </code></pre>
  
  <p>Which would be the SQL query? I have no idea of how to join fields Id_Referee1 and Id_Referee2...</p>
  
  <p>THANKS</p>