An extractor used when planning the physical execution of an aggregation. Compared with a logical
aggregation, the following transformations are performed:
Unnamed grouping expressions are named so that they can be referred to across phases of
aggregation
Aggregations that appear multiple times are deduplicated.
The computation of the aggregations themselves is separated from the final result. For
example, the count in count + 1 will be split into an AggregateExpression and a final
computation that computes count.resultAttribute + 1.
An extractor used when planning the physical execution of an aggregation. Compared with a logical aggregation, the following transformations are performed:
countincount + 1will be split into an AggregateExpression and a final computation that computescount.resultAttribute + 1.