Hello All,
I'm in need of some assistance with creating a rolling sum to find the sum of 3 previous months gas production. Below is an example of the basic data I will be using to find the sum.


OperatorID RRCID YearReported MonthReported YearCode DateReported GasProduction
710549 93207 2012 2 201202 2012-02-01 89
710549 93207 2012 1 201201 2012-01-01 721
710549 93207 2011 12 201112 2011-12-01 353
710549 93207 2011 11 201111 2011-11-01 409
710549 93207 2011 10 201110 2011-10-01 544
710549 93207 2011 9 201109 2011-09-01 707
710549 93207 2011 8 201108 2011-08-01 506
710549 93207 2011 7 201107 2011-07-01 536
710549 93207 2011 6 201106 2011-06-01 472

I want the sum of the Year & Month of 2012-2 to be the sum of the gas production for 2012-1, 2011-12, and 2011-11.

Why not select the sum of gas production where the yearcode is greater than 201111?

Maybe i misunderstand something?