title: Is it possible to use the same table twice in a select query?
body: <p>Hi I have the following query, and I'm wondering what it means:</p>
  
  <pre><code>SELECT c1.id as sender, c2.id as replier
     FROM contacts c1, contacts c2;
  </code></pre>
  
  <p>How can you use the same table twice?</p>