for a Category,I have to get previous Value in the same date of previous quarter .
=> Previous value is aggr for a category to pick value for Addmonths(Date, -3)
For eg:
Date, Value, Category, Previous Value
3/1/2011, 50, A, 0
6/1/2011, 60, A, 50
3/21/2012, 89, A, 0
6/21/3013, 56, A, 89
6/1/2012, 100, B, 0
9/1/2012, 150, B, 100
12/1/2012, 125, B, 150
3/15/2013, 190, B, 0
6/15/2013, 140, B, 190
12/1/2013, 165, A, 0
