取得平均薪水最高的部门的部门名称

select t.deptno,max(avgsal),d.dname from (select deptno,avg(sal) as avgsal from emp group by deptno) tjoin dept don t.deptno = d.deptno

或者另外一种方法也可以

select t.deptno,t.avgsal,d.dname from (select deptno,avg(sal) as avgsal from emp group by deptno order by avgsal desc limit 1) tjoin dept don t.deptno = d.deptno