title: Select row twice with one column modification
body: <p>I have table and sql (running on Oracle):</p>
  
  <p>T (it's just an example, the table is huge)</p>
  
  <pre><code>a  b  c
  -------
  1  4  7
  2  5  5
  3  6  8
  </code></pre>
  
  <p>sql:</p>
  
  <pre><code>SELECT a, b, c
  FROM t
  
  union all
  
  SELECT 'R',b,c
  FROM t
  WHERE b = c AND (condition to another tables, etc)
  </code></pre>
  
  <p>It returns:</p>
  
  <pre><code>1  4  7
  2  5  5
  3  6  8
  R  5  5
  </code></pre>
  
  <p>Is it possible to avoid UNION here (and don't add JOIN)? In other words - is it possible to optimize the query to avoid Oracle look into table T twice?</p>