MDX Help With Sets

Hello,

I'm new to MDX and was hoping someone could answer this question. I'm working on an MDX query, a simplified version is below.

What I'm trying to do is to pull 2 sets, based on a date range. Based on those, I'd like to see the total "cost" measure for each set, and divide one by another.

What I'm finding is that when I run the query below, the cost is broken out by month. So, my select statement gives me the cost for January 2008 and February 2008 in the CurrentPeriod set, and for January, February, etc. 2007 in the PriorPeriodData set. What I want instead is to get the total "cost" measure for all the months in each set. I believe this is what I'd get if I put the date range in a subcube or a where clause - but in that case, I wouldn't be working with 2 distinct sets.

Is there some other way to write this, or to combine all the months in the set before the measures?



WITH

SET [CurrentPeriod] AS

'{[Activity Date].[Date].&[2008-01-01T00:00:00]:[Activity Date].[Date].&[2008-02-01T00:00:00]}'

SET [PriorPeriod] AS

'{[Activity Date].[Date].&[2007-01-01T00:00:00]:[Activity Date].[Date].&[2007-12-01T00:00:00]}'

MEMBER [Measures].[Cost Variance] AS

'([CurrentPeriod],[Measures].[Cost]) /

([PriorPeriodData],[Measures].[Cost])'

SELECT NON EMPTY {

([CurrentPeriod],[Measures].[Cost]),

([PriorPeriodData],[Measures].[Cost]),

([Measures].[Cost Variance])

} ON COLUMNS

FROM [Cube]


Thanks for your help!