title: How to get difference between 2 columns
body: <p>I have a query that is producing something like this:</p>
  
  <pre><code>StartTimestamp  |  EndTimestamp
  ================================
  100             | 450
  --------------------------------
  150             | 500
  </code></pre>
  
  <p>I'd like the result to also include the difference between EndTimestamp and StartTimestamp:</p>
  
  <pre><code>StartTimestamp  |  EndTimestamp  |  Difference
  ==============================================
  100             | 450            | 350
  ----------------------------------------------
  150             | 600            | 450
  </code></pre>
  
  <p>How do I do this in MySQL?</p>