Step: GROUP BY
If the GROUP BY keyword is used, or there is implicit grouping due to the
- use of aggregates in the projection, then grouping is performed by the
- Group function.
+ use of aggregates in HAVING or ORDER BY clauses, or in the
+ projection, then grouping is performed by the Group function.
In this case, before grouping, the solution set is converted into a solution
sequence by applying the ToList function.
Next, the Group function