title: Number of days between two given dates
body: <p>How do I calculate number of days between the to dates strictly using HQL alone. </p>
  
  <p>supposing <code>Current_Date</code> and <code>Expiry_Date</code> are two dates fetched from database. I want to calculate days between <code>Current_Date</code> and <code>Expiry_Date</code>. </p>
  
  <p>Also, How will I handle, if any of the value is <code>null</code> ?</p>