https://cwiki.apache.org/confluence/display/Hive/Enhanced+Aggregation%2C+Cube%2C+Grouping+and+Rollup
GROUP BY a, b, c WITH CUBE is equivalent to
GROUP BY a, b, c GROUPING SETS ( (a, b, c), (a, b), (b, c), (a, c), (a), (b), ©, ( )).
ROLLUP clause is used with GROUP BY to compute the aggregate at the hierarchy levels of a dimension.
GROUP BY a, b, c with ROLLUP assumes that the hierarchy is “a” drilling down to “b” drilling down to “c”.
GROUP BY a, b, c, WITH ROLLUP is equivalent to GROUP BY a, b, c GROUPING SETS ( (a, b, c), (a, b), (a), ( )).
