title: MySQL sum values of a row
body: <p>This query add user points for g1 and g2, I would like to insert the sum of these 2 values in another column called 'total_points'. I realized I can't use SUM(), because they're many columns but just one row. 
  What's the best way to do this?
  I currently have this query:</p>
  
  <pre><code> $query = "UPDATE `points` SET g1 = $g1 + 10, g2 = $g2 + 10 WHERE username = '$username'";
  </code></pre>
  
  <p>Assuming I have this values:</p>
  
  <pre><code>$g1 = '50'; $g2 = '25';
  </code></pre>