The hive Groupby output is not included in the Groupby field

Today to help colleagues test, found in the code has a good hive function:

Collect_set can output fields that are not included in the GroupBy. The condition is that this field value corresponds to the primary key being unique.

Select   A,  collect_set (b) [0],  count (*)          --also want to output the B field corresponding to each primary key from (   select ' A ' A, ' B ' b from   Test.dual) Agroup by A;                                   --According to a group by

　　

The hive Groupby output is not included in the Groupby field