title: adding a custom calculated field for custom search screens in lightswitch
body: <p>so i have this application where i have to create a simple Search screen based on a query <strong>(this query gets all financial transactions for specified search criteria )</strong></p>
  
  <p>so what i want is to add a calculated field on the screen that shows <strong>the sum of the search results.</strong> 
  not  the sum of all records.</p>
  
  <p>i tried to add a calculated field on the financial transactions table but it doesn't make any sense ..</p>
  
  <p>what should i do in these kind of situations ? </p>
  
  <p>thanks in advance.</p>
  
  <p>Regards,</p>