title: MySQL SUM values of difference between two columns
body: <p>I have two columns in one of my tables called TIME_OUT and TIME_IN.  These are both decimal values.  I basically want to sum the difference of these columns.  I have the query below that outputs the difference with no issue, but I'd like to then SUM the difference:</p>
  
  <pre><code>SELECT (TIME_IN-TIME_OUT) AS DIFF FROM TABLE_timelogs WHERE YEAR(LOG_DATE) = YEAR(NOW());
  
  +------+
  | DIFF | 
  +------+
  | 10.0 |
  |  4.0 |
  |  3.0 |
  +------+
  </code></pre>
  
  <p>Is there a way to integrate SUM into the query so that the ultimate output is 17.0?  Thank you in advance!</p>