title: What's wrong with this simple MySQL syntax? Summing the dates
body: <p>Among the rest, I've got three columns in my table:</p>
  
  <p><code>start</code>- <strong>timestamp</strong>, the default value is <code>CURRENT_TIMESTAMP</code></p>
  
  <p><code>duration</code>- <strong>datetime</strong>, usually <code>0000-00-07 00:00:00</code> (one week)</p>
  
  <p><code>end</code> - <strong>timestamp</strong>, the default value is <code>0000-00-00 00:00:00</code></p>
  
  <p>Here's what I do:</p>
  
  <pre><code>UPDATE `banners` SET `end` = `start` + `duration` WHERE `id` = 93
  </code></pre>
  
  <p>No errors appear, the <code>id</code> is exact - but the operation doesn't execute, the <code>end</code> field just remains at zeros.</p>
  
  <p>What's wrong? Any quotes, brackets needed? I also tried making the middle field the <strong>timestamp</strong> type as well with no result.</p>