ASA SQL User's Guide
  Query Optimization and Execution
    Query execution algorithms

Grouping

Grouping algorithms compute a summary of their input. They are applicable only if the query contains a GROUP BY clause, or if the query contains aggregate functions (such as SELECT COUNT(*) FROM T).

For more information, see Hash group by, Ordered group by, Indexed group by, and Single group by.

Hash group by
Ordered group by
Indexed group by
Single group by