title: django.db aggregation across multiple fields
body: <p>I have a table like so:</p>
  
  <pre><code>ID state  A    B    C
  ----------------------
  1   MD    x    x    x
  
  2   MD    x    x    x
  
  3   WA    x    x    x
  
  4   KY    x    x    x
  </code></pre>
  
  <p>I would like to filter by state, and return the sum of B and C. I can get the sums for B or C individually like so:</p>
  
  <pre><code>Table.objects.filter(state=MD).aggregate(x=Sum('B'))
  </code></pre>
  
  <p>I can get the data for B and C like so:</p>
  
  <pre><code>Table.objects.filter(state=MD).values('B', 'C')
  </code></pre>
  
  <p>I'm looking for a way to combine the two operations without resorting to raw SQL.</p>