title: Complicated mySQL Query Order By
body: <p>Example Data:</p>
  
  <pre>
  ╔════╦════════════╦════════════╦═══════╦═══════════╦════════╗
  ║ ID ║   START    ║    STOP    ║ USER  ║   FILE    ║  SIZE  ║
  ╠════╬════════════╬════════════╬═══════╬═══════════╬════════╣
  ║  1 ║ 1330133409 ║ 1330133410 ║ user1 ║ file1.zip ║ 300000 ║
  ║  2 ║ 1330133409 ║ 1330133410 ║ user1 ║ file2.zip ║ 300500 ║
  ║  3 ║ 1330133409 ║ 1330133410 ║ user2 ║ file1.zip ║ 300000 ║
  ║  4 ║ 1330133409 ║ 1330133410 ║ user2 ║ file2.zip ║ 300500 ║
  ║  5 ║ 1330133409 ║ 1330133410 ║ user1 ║ file3.zip ║ 500000 ║
  ║  6 ║ 1330133409 ║ 1330133310 ║ user6 ║ file3.zip ║ 500000 ║
  ╚════╩════════════╩════════════╩═══════╩═══════════╩════════╝
  </pre>
  
  <p>I need to create a MySQL query that computes <code>PER_USER_AVERAGE_BANDWIDTH</code> where <code>PER_USER_AVERAGE_BANDWIDTH = SUM(SIZE) / (STOP - START)</code>, and then order by <code>PER_USER_AVERAGE_BANDWIDTH</code> to produce results like this:</p>
  
  <pre>
  ╔═══════╦════════════════════════════╗
  ║ USER  ║ PER_USER_AVERAGE_BANDWIDTH ║
  ╠═══════╬════════════════════════════╣
  ║ user3 ║ 110.37                     ║
  ║ user1 ║ 100.25                     ║
  ║ user2 ║ 75.70                      ║
  ╚═══════╩════════════════════════════╝
  </pre>
  
  <p>Clear as mud ;) Anyone?</p>