title: How to get difference between two consecutive rows for a column field using group by and order by
body: <p>EmpNo   Dept    Sales
  1   10  9
  2   20  7
  1   10  10
  1   10  5
  3   10  3
  3   10  8
  1   10  11
  4   30  5
  4   30  5</p>
  
  <p>EmpNo   Dept    Sales   Growth
  1   10  5   5
  1   10  9   4
  1   10  10  1
  1   10  11  1
  3   10  3   3
  3   10  8   5
  2   20  7   7
  4   30  5   5
  4   30  6   1</p>