GROUPING SETS 允许你为多个列组合生成分组汇总。它类似于多个 GROUP BY 子句的 UNION ALL 操作，但更加简洁和高效

首先：创建表及接入测试数据

create table students
(id number(15,0),
area varchar2(10),
stu_type varchar2(2),
score number(20,2));
insert into students values(1, '111', 'g', 80 );
insert into students values(1, '111', 'j', 80 );
insert into students values(1, '222', 'g', 89 );
insert into students values(1, '222', 'g', 68 );
insert into students values(2, '111', 'g', 80 );
insert into students values(2, '111', 'j', 70 );
insert into students values(2, '222', 'g', 60 );
insert into students values(2, '222', 'j', 65 );
insert into students values(3, '111', 'g', 75 );
insert into students values(3, '111', 'j', 58 );
insert into students values(3, '222', 'g', 58 );
insert into students values(3, '222', 'j', 90 );
insert into students values(4, '111', 'g', 89 );
insert into students values(4, '111', 'j', 90 );
insert into students values(4, '222', 'g', 90 );
insert into students values(4, '222', 'j', 89 );
commit;

sql示例：

select id, area, stu_type, sum(score) score
from students
group by grouping sets((id, area, stu_type), (id, area), id)
order by id, area, stu_type;

1. (id, area, stu_type)：按照 id、area 和 stu_type 三个字段进行分组，求出每个分组的 score 总和。
2. (id, area)：按照 id 和 area 两个字段进行分组，求出每个分组的 score 总和。
3. id：仅按照 id 字段进行分组，求出每个分组的 score 总和。

GROUPING SETS 等效于 UNION ALL 的写法 

select * from (select id, area, stu_type, sum(score) from students group by id, area, stu_typeunion allselect id, area, null, sum(score) from students group by id, areaunion allselect id, null, null, sum(score) from students group by id
) order by id, area, stu_type;

 总结：

• GROUPING SETS 是一种非常强大的 SQL 分组和聚合工具，它让我们能够在同一个查询中对多种不同的列组合进行聚合，避免了重复编写多个 GROUP BY 子句的麻烦，并且比使用 UNION ALL 更加高效。理解 GROUPING SETS 可以帮助我们在分析数据时获得更多层次的汇总信息。

• GROUPING SETS：提供了最大的灵活性，允许你指定任意的列组合进行分组汇总。你可以精确地控制哪些列组合需要进行聚合，而不像 ROLLUP 或 CUBE 那样会自动生成所有的汇总维度。