wrong result of parallelperiod() for DATE in MDX

Question

I want to extract data for same period last year and last month. for this i am using Parallelperiod(), for eg

PARALLELPERIOD([date].[year],1,[date].[date].[20-Sep-2014]) , 

for which I am getting output : 21-Sep-2014

and

PARALLELPERIOD([date].[month],1,[date].[date].[20-Sep-2014]) , 

for which I am getting output : 16-Aug-2014

Same function would throw some other date for some other month

Can you guide about the issue, where i am doing wrong or if there is some other alternative to this?

Answer 1

You must have some dates that do not exist in the cube.

What the PARALLELPERIOD function is doing is saying ok we are 262 members at the [date] level into 2014 - then it goes to 2013 and finds the member at the [date] level that is also 262 members in. Therefore unless you have complete sets of dates in your cube this function will return surprising results.

Therefore the solution is to ensure that all historical dates are represented in the cube. These extra dates should not cause any extra overhead as they will be creating empty space in the cube which is dealt with very well by SSAS