title: Join two sql queries
body: <p>I have two SQL queries, where the first one is:</p>
  
  <pre><code>select Activity, SUM(Amount) as "Total Amount 2009"
  from Activities, Incomes
  where Activities.UnitName = ? AND
        Incomes.ActivityId = Activities.ActivityID
  GROUP BY Activity
  ORDER BY Activity;
  </code></pre>
  
  <p>and the second one is:</p>
  
  <pre><code>select Activity, SUM(Amount) as "Total Amount 2008"
  from Activities, Incomes2008
  where Activities.UnitName = ? AND
        Incomes2008.ActivityId = Activities.ActivityID
  GROUP BY Activity
  ORDER BY Activity;
  </code></pre>
  
  <p>(Dont mind the '?', they represent a parameter in birt).
  What i want to achieve is the following:
  I want an SQL query that returns the same as the first query, but with an additional (third) column which looks exactly like "Total Amount 2008" (from the 2nd query).</p>