Creating Count Distinct Calculation in DMR

[Cognos91]

All,

I have a requirement to calculate count distinct (data item 1) when (data item 2 is null and not null).
This calculation works perfectly fine in a relational model. I created a new data item (data item 1 - which is the ID being counted) and Data Item 2 (which is the flag based on a secondary ID being null / not null). The report displays the count distinct values correctly.

However, when I drag the measure (that is Data Item 1) in my regular dimension and use Data Item 2 as a separate query subject in my DMR, then this calculation does not work correctly. I am getting a total of the count of IDs that is contained in my fact table.

How should a count distinct calculation be included in DMR?

Thanks

[Cognos91]

The calculation in DMR was created in the regular measure dimension. There was no need to create a separate calculated measure.