title: ORACLE SQL Query only Overlapping Timeframes
body: <p><strong>Data From <code>Emp</code> table:</strong></p>
  
  <pre><code>NUM  DEPT   HIRED_SDT                       HIRED_EDT
  ---  -----  ------------------------------  ------------------------------
  1    Sales  October, 01 2012 11:00:00+0000  October, 01 2012 11:30:00+0000
  2    Sales  October, 01 2012 11:22:00+0000  October, 01 2012 12:40:00+0000
  3    Sales  October, 01 2012 13:00:00+0000  October, 01 2012 13:50:00+0000
  4    CC     October, 01 2012 14:00:00+0000  October, 01 2012 15:00:00+0000
  5    CC     October, 01 2012 15:00:00+0000  October, 01 2012 16:10:00+0000
  6    CC     October, 01 2012 16:00:00+0000  October, 01 2012 17:20:00+0000
  </code></pre>
  
  <p><strong>Desired Result:</strong></p>
  
  <p>Only the overlapping timeframes grouped per departement </p>
  
  <p>==> eg. within <code>Sales</code> there are 2 out of 3 records overlapping</p>
  
  <pre><code>NUM  DEPT   HIRED_SDT                       HIRED_EDT
  ---  -----  ------------------------------  ------------------------------
  1    Sales  October, 01 2012 11:00:00+0000  October, 01 2012 11:30:00+0000
  2    Sales  October, 01 2012 11:22:00+0000  October, 01 2012 12:40:00+0000
  5    CC     October, 01 2012 15:00:00+0000  October, 01 2012 16:10:00+0000
  6    CC     October, 01 2012 16:00:00+0000  October, 01 2012 17:20:00+0000
  </code></pre>
  
  <p><a href="http://sqlfiddle.com/#!4/91730/1" rel="nofollow">http://sqlfiddle.com/#!4/91730/1</a></p>