Count Distinct in CE_AGGREGATION?

Is there a way to use Count Distinct in CE_AGGREGATION?

I tried

var_out = CE_AGGREGATION(:var, [COUNT(DISTINCT "A") as "COUNT"], ["B", "C"]);

to get the number of distinct values of "A" for each combination of "B" and "C", but activation fails.

My workaround currently is to use two aggregations:

var_dummy = CE_AGGREGATION(:var, [COUNT("A") as "DUMMY"], ["A", "B", "C"]);

var_out = CE_AGGREGATION(:var_dummy, [COUNT("A") as "COUNT"], ["B", "C"]);

It works well but I am not sure if this is the most efficient way to do it (performance).

For example, would it be better to get :var from an analytical view (already aggregated to columns "A", "B", "C" --> only one CE_AGGREGATION needed) instead of using CE_COLUMN_TABLE and two aggregations?

Thanks for your Feedback,

Fabian