How to perform a Distinct Sum using MDX? - mdx

Question

So I have data like this:
Date EMPLOYEE_ID HEADCOUNT TERMINATIONS
1/31/2011 1 1 0
2/28/2011 1 1 0
3/31/2011 1 1 0
4/30/2011 1 1 0
...
1/31/2012 1 1 0
2/28/2012 1 1 0
3/31/2012 1 1 0
1/31/2012 2 1 0
2/28/2011 2 1 0
3/31/2011 2 1 0
4/30/2011 2 0 1
1/31/2012 3 1 0
2/28/2011 3 1 0
3/31/2011 3 1 0
4/30/2011 3 1 0
...
1/31/2012 3 1 0
2/28/2012 3 1 0
3/31/2012 3 1 0
And I want to sum up the headcount, but I need to remove the duplicate entries from the sum by the employee_id. From the data you can see employee_id 1 occurs many times in the table, but I only want to add its headcount column once. For example if I rolled up on year I might get a report using this query:
with member [Measures].[Distinct HeadCount] as
??? how do I define this???
select { [Date].[YEAR].children } on ROWS,
{ [Measures].[Distinct HeadCount] } on COLUMNS
from [someCube]
It would product this output:
YEAR Distinct HeadCount
2011 3
2012 2
Any ideas how to do this with MDX? Is there a way to control which row is used in the sum for each employee?

Answer 1

You can use an expression like this:
WITH MEMBER [Measures].[Distinct HeadCount] AS
Sum(NonEmpty('the set of the employee ids', 'all the dates of the current year (ie [Date].[YEAR].CurrentMember)'), [Measures].[HeadCount])
If you want a more generic expression you can use this:
WITH MEMBER [Measures].[Distinct HeadCount] AS
Sum(NonEmpty('the set of the employee ids',
Descendants(Axis(0).Item(0).Item(0).Hierarchy.CurrentMember, Axis(0).Item(0).Item(0).Hierarchy.CurrentMember.Level, LEAVES)),
IIf(IsLeaf(Axis(0).Item(0).Item(0).Hierarchy.CurrentMember),
[Measures].[HeadCount],
NULL))