Semi-addidtive measures
- can be aggregated/summed across certain measures but not others. E.g. re-order level in stock-ox. Makes no sense to sum it over time whereas profit makes total sense to sum over periods.
The aggregatefunction property of the measure will dictate how they are aggregated - e.g. lastChild, avg, min, count etc...A dimension of type 'TIME' is required for semi-additive measures to function.
NULL Values - may occur when dimensions not processed properly and will result in you pulling your hair out, wondering why the ALL level produces results but lower levels have NULLS. Make sure processing all dimensions used in a query is near the top of your list of TODOs when this kind of thing occurs!