title: Conversion of String having date format with AM/PM to DD-MM-YYYY HH24:MI:SS format
body: <p>Might be simple but I am unable to resolve this.</p>
  
  <p>I want to do a minus the date between 2 tables for validation- 
  One is an external table.
  The external table has varchar2 for date column -format is 3/03/2014 6:00:28 AM
   table2 has a date datatype which is of format '03-MAR-2014 06:00:28'.</p>
  
  <p>Can someone help me with this. I am getting errors like ORA29913, ORA 01830 etc while doing minus between 2 after doing a to_date of first string</p>
  
  <p>Thanks,</p>