title: Updating a sql table with new column
body: <p>I am using mysql and I have a table with columns: postid, userid, datestamp</p>
  
  <p>I want to create a new column called 'entry' that numbers the entries chronologically according to datestamp</p>
  
  <p>So, for the rows:</p>
  
  <pre><code>3705    1   2003-12-08 13:42:13
  3711    15  2003-11-12 15:22:01
  3701    2   2004-01-11 01:22:12
  </code></pre>
  
  <p>I want to end up with:</p>
  
  <pre><code>3705    1   2003-12-08 13:42:13 2
  3711    15  2003-11-12 15:22:01 1
  3701    2   2004-01-11 01:22:12 3
  </code></pre>
  
  <p>How can I perform this task?</p>