Measure Aggregation at SELECT level vs Projection level

Aggregation at SELECT level:  starts when a query is created by an user, a reporting tool creates the SQL and sends a SELECT statement with GROUP BY (selected dimension column in Query) to the database. Then the data is returned to a microcube where the first level of aggregation occurs, the microcube projects the aggregated data onto a report, the SQL is run and the microcube gets the results.

Aggregation at projection level: This aggregation working in the report level(Microcube level). When you remove a one column from the report this aggregation works .

Every measure object should have an aggregation function. Each aggregation operation typically gets combined with an appropriate projection function as well. Most of the aggregation + projection function pairs make sense. Here is the chart that shows the typical matches.

Aggregation at SELECT Level	Aggregation Projection Level
Sum	Sum
Min	Min
Max	Max
Count	Sum
Avg	None or Avg