This operator represents the grouping of rows.
Operator name: GRPBY
Represents: The grouping of rows according to common values of designated columns or functions. This operation is required to produce a group of values, or to evaluate set functions.
If no GROUP BY columns are specified, the GRPBY operator can still be used if there are aggregation functions in the SELECT list, indicating that the entire table is treated as a single group when doing that aggregation.