title: SQL: order by column alias
body: <p>When I run this query:</p>
  <pre><code>SELECT 'A' as table_name, count() FROM A 
  UNION ALL SELECT 'B' as table_name, count() FROM B
  UNION ALL SELECT 'C' as table_name, count() FROM C ORDER BY table_name ASC;
  </code></pre>
  <p>The output is:</p>
  <pre><code>table_name  count
  -----------------
  B            0
  C            0
  A            0
  </code></pre>
  <p>It doesn't order by column table_name, how can I order it and get the output:</p>
  <pre><code> table_name  count
   -----------------
    A            0
    B            0
    C            0
  </code></pre>