慕课网笔记（增强型 group by ）

分组函数的嵌套
目的：求部门平均工资的最大值

select max(avg(sal)) from emp group by deptno;

GROUP BY 语句的增强

select deptno,job,sum(sal) from emp group by deptno,job order by deptno;
select sum(sal) from emp group by deptno;
select sum(sal) from emp;

以上等于

select deptno,job,sum(sal) from emp group by rollup(deptno,job);

group by rollup(a,b)
等价于：
group by a,b
+
group by a
+
group by null