title: Select newest entry from each column
body: <p>I have a SQL table about as follows:</p>
  
  <pre><code>id | timestamp | position | size | level
  </code></pre>
  
  <ul>
  <li><code>id</code> is the primary key and will always have a value</li>
  <li><code>timestamp</code> is a numerical time representation</li>
  <li><code>position</code>, <code>size</code> and <code>level</code> may have a value, or they may be null</li>
  </ul>
  
  <p>I want to execute a query which will get the newest non-null position, size and level as determined by the timestamp in the row it belongs to.</p>
  
  <p>How do I do that?</p>