title: Use 'as' multiple times
body: <p>I have this:</p>
  
  <pre><code>SELECT
     posts.id,
     (SELECT COUNT(*) FROM votes WHERE votes.post = posts.id) AS votesCount,
     (SELECT SUM(vote) FROM votes WHERE votes.post = posts.id) AS votesUp
  FROM posts WHERE posts.id = 1
  </code></pre>
  
  <p>How do i get the difference between <strong>votesCount</strong> and <strong>votesUp</strong> without doing other SELECT? Something like:</p>
  
  <pre><code>SELECT
     posts.id,
     (SELECT COUNT(*) FROM votes WHERE votes.post = posts.id) AS votesCount,
     (SELECT SUM(vote) FROM votes WHERE votes.post = posts.id) AS votesUp,
     votesCount - votesUp AS votesDown
  FROM posts WHERE posts.id = 1
  </code></pre>
  
  <p>Is it possible, or do i have to call another SELECT anyway?
  Thanks.</p>
  
  <p>Btw, sorry for my bad english.</p>