【Hive】Hive高級聚合（grouping sets、rollup、cube）

Hive高級聚合（0.10開始支持）

高級聚合功能相當於group by 加強

grouping sets：多個group by 進行union all，在同一個數據集進行多重group by
      該關鍵字可以實現同一數據集的多重group by操作。事實上GROUPING SETS是多個GROUP BY進行UNION ALL操作的簡單表達，它僅僅使用一個stage完成這些操作。GROUPING SETS的子句中如果包含()數據集，則表示整體聚合。

select name,work_space[0] from employee group by name, work_space[0] grouping sets((name,work_space[0]),name,());

// 上面語句與下面語句等效

select name, work_space[0] as main_place, count(employee_id) as emp_id_cnt

from employee

group by name, work_space[0]
UNION ALL
select name, work_space[0] as main_place, count(employee_id) as emp_id_cnt

from employee

group by name

UNION ALL
select name, work_space[0] as main_place, count(employee_id) as emp_id_cnt

from employee;

rollup  

group by a,b,c with rollup <=> grouping sets((a,b,c),(a,b),(a),())

cube

group by a,b,c with cube <=> grouping sets((a,b,c),(a,b),(a,c),(b,c),(a),(b),(c),())

參考：https://www.jianshu.com/p/9502e1d58f45