title: PLSQL - How to subtract time (hh:mi) on timestamp type
body: <p>I have two fields with timestamps type, time_in and time_out.<br>
  For example:<br> 
  <code>time_out = 02-MAY-11 07.30.00.000000 PM</code> and <br> <code>time_in = 02-MAY-11 07.57.00.000000 AM</code><br><br>
  I want to get the different HOURS from that timestamps field.<br>How to do that,.?</p>