title: Subtract two Columns from a Specific Row
body: <p>I have a table similar to the one below:</p>
  
  <pre>
  <b>ID</b>    <b>Vote_Up</b>    <b>Vote_Down</b>   <b>Vote_Total</b>
  1         3            1             2
  2         1            3            -2
  3         23           7             16
  4         5            1             4
  5         7            5             2
  6         2            2             0
  7         9            1             8
  </pre>
  
  <p>How do i Come up with the Vote_Total?</p>