title: Using a subquery in SELECT clause with a join of a table to itself
body: <p>Trying to create a subquery in the SELECT clause (using Oracle 11g). The subquery includes a join of a table to itself. I'm getting an "ORA-01427: single-row subquery returns more than one row" error message (my worst enemy...). Here's my code:</p>
  
  <pre><code>SELECT e.ISBN,
  (SELECT p2.PAGE_NUMBERS FROM PAGE_NUMBERS_TABLE p1 INNER JOIN PAGE_NUMBERS_TABLE p2
      ON p1.TITLE_CODE = p2.TITLE_CODE
      AND p2.FORMAT_CODE = 'HB'
      WHERE p1.FORMAT_CODE = 'OC') AS "Page Numbers"
      FROM ISBN_TABLE e
  </code></pre>
  
  <p>Hope this makes sense, I can clarify further on what I am looking to do here if it doesn't make sense.</p>
  
  <p>Thanks!</p>