grouping sets 的使用

grouping sets 可以用于在计算分组聚合函数值的同时计算合计值

-- 查询结果group_id为NULL的那一行即为合计值
select
    group_id
    , count(distinct user_id) as user_num
from table_name
group by group_id
grouping sets ((group_id),())

参考资料：

https://blog.****.net/u013053796/article/details/18620631

https://www.cnblogs.com/ToDoToTry/p/5474231.html

Hive分析窗口函数：http://lxw1234.com/archives/2015/04/193.htm