title: Using alias in sql to compute other value
body: <p>I've this query. I want to perform addition on Total1 and Total2 which are aliases. My query is not working  mysql is showing Unknown column error.</p>
  
  <pre><code>SELECT p.Quantity*p.Price AS Total1,
         p.Quantity+p.Tax AS Total2,
         p.Total1+p.Total2 AS Total
  FROM p
  ORDER BY id
  </code></pre>