title: Mysql SUM of SUM
body: <p>Is it possible to make a sum of sum in one select query?</p>
  
  <p>Something like this:</p>
  
  <pre><code>SELECT id, SUM(current_price - bought_price)*amount AS profit FROM purchase WHERE purchase_id = 1 GROUP BY id 
  </code></pre>
  
  <p>I want the sum of all returned <code>profit</code></p>