title: SQL Shift column down 1 row
body: <p>I am trying to subtract a value from a past time period with the value in the present time period. </p>
  
  <p>*This is what I have:</p>
  
  <pre><code>Date,  present, past (identical to present)
   Jan,   100,        100
   Feb,   200,        200
  March,  300,        300
  April,  400,        400
  </code></pre>
  
  <p>*This is what I want;</p>
  
  <pre><code>Date,  present, past (past column shifted down 1 row)
  
       Jan,    100,       0
       Feb,   200,        100
      March,  300,        200
      April,  400,        300
  </code></pre>
  
  <p>Sample of code:</p>
  
  <pre><code>SELECT
        [month],
        sum([money]) as present,
        sum([money]) as past
  FROM database
  group by [month]
  </code></pre>