SSAS - Sum of Top or Bottom - sum

Question

SELECT
[Measures].[Internet Sales Amount] ON COLUMNS
,Tail
(
[Date].[Calendar Year].[Calendar Year].MEMBERS
,2
) ON ROWS
FROM [Adventure Works];
Above MDX query gives me output as :
Year Internet Sales Amount
CY 2003 $9,791,060.30
CY 2004 $9,770,899.74
I understood how this query worked but I want to create Calculated measure in a cube which will always give me sum of bottom 2 years. How to do this? I am a newbie to SSAS. I am good at designing simple measures and dimensions but when it comes to using MDX, I am mostly stuck.
PS: I tried using TopCount, BottomCount etc but here I want to order by "Year", which is a dimension.
Any help would be appreciated.
Thanks,
Parry

Answer 1

The following query calculates a measure for sum the the last 2 years of the Date dimension:
WITH
MEMBER [Measures].[Sales from the last 2 Years]
AS Aggregate( Tail( [Date].[Calendar Year].[Calendar Year].Members, 2)
, [Measures].[Internet Sales Amount]
)
SELECT { [Measures].[Sales from the last 2 Years]
} ON COLUMNS
, { Tail( [Date].[Calendar Year].[Calendar Year].Members, 2)
} ON ROWS
FROM [Adventure Works]
Other interesting query, would be calculating a measure for the sum of each year and its previous:
WITH
MEMBER [Measures].[Sales from 2 years]
AS Aggregate( { [Date].[Calendar Year].CurrentMember.PrevMember
: [Date].[Calendar Year].CurrentMember }
, [Measures].[Internet Sales Amount]
)
SELECT { [Measures].[Internet Sales Amount]
, [Measures].[Sales from 2 years]
} ON COLUMNS
, NON EMPTY
{ [Date].[Calendar Year].[Calendar Year]
} ON ROWS
FROM [Adventure Works]
It does a sum, because the aggregation type of the measure [Measures].[Internet Sales Amount] is Sum, and the Aggregate function aggregates according to the measure's aggregation type.
Key Concepts in MDX
Aggregate function reference
MDX is a hard topic to grasp; if you're starting out, I recommend you read the book MDX Solutions, 2nd edition.