SUMX iterator cardinality reduction to single column

Investigate if the cardinality of the iterated table can be reduced by iterating a single column.

Remarks

The SUMX function iterates an entire table, but the expression evaluated for each row seems related to a single column of the table with a product operation that requires a context transition.

If the result of the measure is additive and consistent even when the context transition has only one value of the column instead of a row of the table, then the iterator cardinality can be reduced to the unique values of the column instead of iterating the entire table. Use DISTINCT to iterate the column values to be consistent with a table reference, or use VALUES to include the blank row if needed for the correct evaluation.

Example

Replace the Customer table reference with DISTINCT on Customer[Discount].

Original code

SUMX ( 
    Customer, 
    Customer[Discount] * [Sales Amount] 
)

Possible optimization

SUMX ( 
    DISTINCT ( Customer[Discount] ), 
    Customer[Discount] * [Sales Amount] 
)