How to Move Qty in Bex query from present month to 'N' month before

Hi All,

Is there any way I can do some formula in BEx query to achieve best result for my issue.

I want to shift qty from one month to another month based on lead time (in months).

example : I have lead time '3' then my quantity shift always 3months ahead if do not have history 3 month then shift to 2 month.

if do not have 2 month before then shift to 1 month before .

if do not have any previous month display then no shifting show in same month.

is possible in BEx Query.

explanation: first month demand 40 qty but even lead time 2 there is no previous month display so required same month '40'

second month 30 qty also lead time 2 but only one month have previous so add to previous month required so added.

third month demand 20 qty also lead time 2 so two month before means 1st month so added to required first month .

4th month deman 20 lead time 2 so two months ahead required so that 2nd month updated with 20.

months

lead time 1 2 3 4

2 demand 40 30 20 20

required 90 20

Now I want formula to achieve Required qty, is there any way we can dynamically get when BEx query run .

if not understand will explain again.

Thanks and Regards,

Harikiran.