title: Use Alias in other column in SELECT statement
body: <p>I am looking to do some basic math on my <code>SELECT</code> query and columns..</p>
  
  <pre><code>SELECT Rider, 
  COUNT(if(Result = 1, Result, NULL)) AS "Firsts", 
  COUNT(if(Result = 2, Result, NULL)) AS "Seconds", 
  COUNT(if(Result = 3, Result, NULL)) AS "Thirds", 
  COUNT(if(Result = " ", Result, NULL)) AS "NP",
  COUNT(*) AS "Total",
  "Firsts"/"Total"*100 AS "S/R"
  FROM meeting_master
  WHERE RaceDayDate&gt;="2012-01-01"
  GROUP BY meeting_master.Rider
  ORDER BY Firsts DESC
  LIMIT 100
  </code></pre>
  
  <p>My problem (and lack of MySQL knowledge) is to have the <code>S/R</code> column calculate the math in the 7th line...</p>