title: Summing by Column
body: <p>Suppose we have the following columns:</p>
  
  <pre><code>       X           Y         Z
      Category     Date      Amount
         A         January   10
         A         February  20
         A         March     30
         B         January   34 
         B         February  45
         B         March     65
         C         January   87
         C         February  98
         C         March     100
         D         January   80
         D         February  90
  </code></pre>
  
  <p>I want to sum the <code> Amount </code> column by <code> Category </code> and <code> Date </code>. So for Category A, we would have the sum of the amount be 10+20+30 = 60 for the dates between January and March. In Oracle BI, how would we do this? Note that Some categories might have missing dates. So I want to sum the Amounts for the only the the available dates between January and March. Category D, for example, has March missing. So the total amount would be 80+90 = 170.</p>
  
  <p>When I do the following, I just get the sum of all the amounts:</p>
  
  <pre><code>   sum("Z"."Amount")
  </code></pre>