How to calculate Moving Sum over 3 months
How can we calulate moving sum from a cube with historical transaction data? For example we want to generate a report in Bex Analyzer with the sum over 3 months as follows:
[Year] [Month] [Issue qty] [Issue qty last 3 months]
2008 Jan 10 10
2008 Feb 19 29
2008 Mar 6 35
2008 Apr 23 48
2008 May 15 44
2008 Jun 17 55
2008 Jul 4 36
So the column [Issue qty last 3 months] for the month of June must contain the total qty issued over June, May and April.
The aggregation for the monthly Issue qty will of course automatically be done by BEx Analyzer, but as far as I can see the aggregation over the last 3 months is not possible in Query Designer or BEx Analyzer (without using "Convert to formula").
Does anyone know how to calculate a moving sum like this (in the Front-End or the Back-End)?