慕課網筆記（增強型 group by ）

分組函數的嵌套
目的：求部門平均工資的最大值

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

GROUP BY 語句的增強

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;

以上等於

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

group by rollup(a,b)
等價於：
group by a,b
+
group by a
+
group by null