Switch between meassure

[oracledw]

Hello,

I have a grid with columns A, B, C and D with a single meassure

I want follwing behavior:

If GRID has only Column A then show meassure M1

If GRID has Column "A" with any other column(s) then show meassure M2

If grid does not have Column "A" then show meassure M2.

M1 = SUM(Salary)

M2 = SUM(Bonus)

Thanks.