求部门平均薪水的等级
- A.求部门平均薪水的等级。
select deptno,avg_sal,grade from
(select deptno,avg(sal) avg_sal from emp group by deptno)t
join salgrade s on(t.avg_sal between s.losal and s.hisal)
- B.求部门平均的薪水等级
select deptno,avg(grade) from
(select deptno,ename, grade from emp join salgrade s on(emp.sal between s.losal and
s.hisal)) t
group by deptno
- C.那些人是经理
select ename from emp where empno in(select mgr from emp);
select ename from emp where empno in(select distinct mgr from emp);
- D.不准用组函数，求薪水的最高值（面试题）
select distinct sal from emp where sal not in(
select distinct e1.sal from emp e1 join emp e2 on (e1.sal<e2.sal));
- E.平均薪水最高的部门编号
select deptno,avg_sal from
(select avg(sal)avg_sal,deptno from emp group by deptno)
where avg_sal=
(select max(avg_sal)from
(select avg(sal) avg_sal,deptno from emp group by deptno)
)
- F.平均薪水最高的部门名称
select dname from dept where deptno=
(
select deptno from
(select avg(sal)avg_sal,deptno from emp group by deptno)
where avg_sal=
(select max(avg_sal)from
(select avg(sal) avg_sal,deptno from emp group by deptno)
)
)
- G.求平均薪水的等级最低的部门的部门名称
组函数嵌套
如：平均薪水最高的部门编号，可以E.更简单的方法如下：
select deptno,avg_sal from
(select avg(sal) avg_sal,deptno from emp group by deptno)
where avg_sal =
(select max(avg(sal)) from emp group by deptno)
组函数最多嵌套两层
分析：
首先求
1.平均薪水： select avg(sal) from group by deptno;
2.平均薪水等级： 把平均薪水当做一张表，需要和另外一张表连接salgrade
select deptno,grade avg_sal from
( select deptno,avg(sal) avg_sal from emp group by deptno) t
join salgrade s on(t.avg_sal between s.losal and s.hisal)
上面结果又可当成一张表。
DEPTNO GRADE AVG_SAL
-------- ------- ----------
30 3 1566.66667
20 4 2175
10 4 2916.66667
3.求上表平均等级最低值
select min(grade) from
(
select deptno,grade,avg_sal from
(select deptno,avg(sal) avg_sal from emp group by deptno)t
join salgrade s on(t.avg_sal between s.losal and s.hisa)
)
4.把最低值对应的2结果的那张表的对应那张表的deptno, 然后把2对应的表和另外一张表做连接。
select dname ,deptno,grade,avg_sal from
(
select deptno,grade,avg_sal from
(select deptno,avg(sal) avg_sal from emp group by deptno)t
join salgrade s on(t.avg_sal between s.losal and s.hisal)
) t1
join dept on (t1.deptno = dept.deptno)
where t1.grade =
(
select deptno,grade,avg_sal from
(select deptno,avg(sal) avg_sal from emp group by deptno) t
join salgrade s on(t.avg_sal between s.losal and s.hisal)
)
)
结果如下：
DNAME DEPTNO GRADE AVG_SAL
-------- ------- -------- --------
SALES 30 3 1566.6667
- H: 视图（视图就是一张表，一个字查询）
G中语句有重复，可以用视图来简化。
conn sys/bjsxt as sysdba;
grant create table,create view to scott;
conn scott/tiger
创建视图：
create view v$_dept_avg-sal_info as
select deptno,grade,avg_sal from
( select deptno,avg(sal) avg_sal from emp group by deptno)t
join salgrade s on 9t.avg_sal between s.losal and s.hisal)
然后
select * from v$_dept_avg-sal_info
结果如下：
DEPTNO GRADE AVG_SAL
-------- ------- ----------
30 3 1566.66667
20 4 2175
10 4 2916.66667
然后G中查询可以简化成：
select dname,t1.deptno,grade,avg_sal from
v$_dept_avg-sal_info t1
join dept on9t1.deptno =dept.deptno)
where t1.grade=
(
select min(grade) from v$_dept_avg-sal_info t1
)