title: Get previous month of a given date sql
body: <p>I had this:</p>
  
  <pre><code>select company
  from alldata
  where **{previous month of date("01.05.2011")}**
  IN
  (select month from alldata where SumNrSpot=0)
  </code></pre>
  
  <p>I need to find the previous month in the <code>where</code> clouse.
  Please, anybody can help?</p>