title: SQL sum a field grouped by same identifier in two different columns
body: <p>The table has 4 columns Match, Winning_Player_ID, Losing_Player_ID, Quantity_Points_Exchanged_for_that_match. I would like to in a single query show the total number of points each player won and earned over all matches. </p>
  
  <p>Here is the table</p>
  
  <pre><code>M WIN LOSE QTY  
  1 100 201 10  
  2 201 100 05  
  3 100 201 05  
  4 302 100 05  
  </code></pre>
  
  <p>For output I would like total it in this way in a single query and cannot figure it out.</p>
  
  <pre><code>ID WIN LOSE
  100 15 10
  201 05 15
  302 05 00
  </code></pre>