My solution was something like this:
DeskI only:
a)
– First of all, You need to drag all the dimensions and measures in the query panel.
– Create one block Table1 with Dimension W and measure B.
– Create another block Table2 with Dimension Y and measure A.
– Next create another block Table3 with Dimension W and Y with A or C.
– Place the blocks on top of each other.
b) You would create a @prompt something like @Prompt{‘Select option:’,‘A’,{‘Dim W’,‘Dim Y’,‘Both’},mono,constrained)
c) Based the on the user input, Let’s assume user has selected ‘Dim W’, then you will display Table1 and HIDE Table2 and Table3 in your report. Similarly you have to do for other selections.
Check this link, I did it long back to display different graphs based on the user selection:
How to show and hide report blocks based on user selection.
BO_Chief 
(BOB member since 2004-06-06)