12 month rolling total routine
I'm looking at building a 12 month rolling total routine with a table which I think makes sense. It would look something like this:
CustomerID | Date | cMonth | Value | CRolling12MonthSummary
Each date would be the first of the month, the cMonth would pull the month (Jan, Feb, Mar) from the date field and the value would be entered manually or uploaded.
How do I get this to do rolling 12 month summaries based on the value? Obviously the first 11 rows of cRolling12MonthSummary are empty, but how do I set the 12 month range which would move +1 for each successive summary row etc?
Thanks in advance