Hash Match and Stream Aggregate Operators in SQL Server

Andy Brownsword rounds up the usual suspects:

In the last post we looked at how TOP and MAX operators compared. We saw the execution plan for a MAX function used a Stream Aggregate operator which is one of two which we can use for aggregation

I wanted to look at the two operators and how they perform the same tasks in different ways. The way they function is key to understanding why the engine may choose to use one over the other and the impact this can have on the performance of a query.

The two operators in question: the Hash Match (Aggregate) and Stream Aggregate

Read on for a discussion of how each operator works and when each makes sense for the optimizer to use.