The Aggregator transformation performs aggregate calculations, such as averages and sums. The Integration Service performs aggregate calculations as it reads and stores data group and row data in an aggregate cache. The Aggregator transformation is an active transformation.

The Aggregator transformation is unlike the Expression transformation, in that you use the Aggregator transformation to perform calculations on groups. The Expression transformation permits you to perform calculations on a row-by-row basis.

When you use the transformation language to create aggregate expressions, you can use conditional clauses to filter rows, providing more flexibility than SQL language.

After you create a session that includes an Aggregator transformation, you can enable the session option, Incremental Aggregation. When the Integration Service performs incremental aggregation, it passes source data through the mapping and uses historical cache data to perform aggregation calculations incrementally.