title: SQL making last year's data into another column
body: <p>I have a data set that looks like:</p>
  
  <pre><code> revenue    country date    
   100    US  3/13/2014
   200    US  3/14/2014
   300    CA  3/13/2014 
   150    US  3/13/2013
   200    CA  3/13/2013
  </code></pre>
  
  <p>How can I run a query to get last year's revenue in the same date into another column?</p>
  
  <pre><code> revenue    country data    revenue_last_year
   100    US  3/13/2014   150
   200    US  3/14/2014   0 or null
   300    CA  3/13/2013   200
  </code></pre>
  
  <p>Thanks in advance!</p>