I have a group which totals some values, in the group I also want to include a sum of the current value plus the 2 previous values. This need to be repeated in each group (the first 2 obviously won't total but that is ok.

Group       Value          90day
1                  10               10
2                    9                19
3                    7                26
4                   1                 17
5                    5                 13

Thanks