GROUPING SETS 함수로 ROLLUP, CUBE 함수를 표현해보자! GROUP BY ROLLUP (A,B) == GROUP BY GROUPING SETS (NULL, (A), (A,B)) == GROUP BY GROUPING SETS ((), (A), (A,B)) GROUP BY CUBE (A,B) == GROUP BY GROUPING SETS (NULL, (A), (B), (A,B)) == GROUP BY GROUPING SETS ((), (A), (B), (A,B))
