title: SQL Delete Rows Based on Multiple Columns
body: <p>I have a table with eight columns including a device ID, a device reading type, and a device reading date. Those three columns would look like this:
  <a href="http://i.stack.imgur.com/VhMQX.jpg" rel="nofollow">Example Table</a></p>
  
  <p>What I would like to do is delete every row for which DevReadType = XX and every row with a matching DevNum but a DevReadDate that is less than the date when DevReadType = 'XX'. I haven't been able to find any examples with this kind of complex conditional. Help would be greatly appreciated!!</p>