多表连接

----求各个部门里薪水最高的人
SQL> select ename, sal from emp
  2  join (select deptno, max(sal) max_sal from emp group by deptno) t
  3  on (emp.deptno = t.deptno and emp.sal = t.max_sal);


----求各个部门平均薪水的等级
SQL> select deptno, avg_sal, grade from
  2  (select deptno, avg(sal) avg_sal from emp group by deptno) t
  3  join salgrade s on (t.avg_sal between s.losal and s.hisal);


----求各个部门平均的薪水等级（没人薪水等级的平均数）
SQL> select deptno, avg(grade) from
  2  (select  deptno, grade from emp join salgrade on (sal between losal and hisal)) t
  3  group by deptno;


----求雇员中谁是经理
SQL> select distinct ename from emp where empno in (select mgr from emp);


—---不用组函数求薪水的最大值
SQL> select distinct sal from emp
  2  where sal not in (select distinct e1.sal from emp e1 join emp e2
  3  on (e1.sal < e2.sal));


----求平均薪水最高的部门的部门编号
SQL> select deptno from
  2  (select deptno, avg(sal) avg_sal from emp group by deptno)
  3  where avg_sal = (select max(avg_sal) from (select deptno, avg(sal) avg_sal from emp group by deptno));// = 部门平均薪水的最大值
或者：
SQL> select deptno from
  2  (select deptno, avg(sal) avg_sal from emp group by deptno)
  3  where avg_sal = (select max(avg(sal)) from emp group by deptno);


----求平均薪水最高的部门的部门名称
//SQL> select dname from dept where deptno = 平均薪水最高的部门的部门编号;


SQL> select dname from dept where deptno =
  2  (select deptno from (select deptno, avg(sal) avg_sal from emp group by deptno)
  3  where avg_sal = (select max(avg_sal) from (select deptno, avg(sal) avg_sal from emp group by deptno)));


----求平均薪水等级最低的部门的部门名称
SQL> select deptno, avg(sal) avg_sal from emp group by deptno;//求部门平均薪水


    DEPTNO    AVG_SAL
---------- ----------
        30 1566.66667
        20       2175
        10 2916.66667


SQL> select deptno, grade gra from//求部门平均薪水等级
  2  ( select deptno, avg(sal) avg_sal from emp group by deptno )
  3  join salgrade on (avg_sal between losal and hisal);


    DEPTNO        GRA
---------- ----------
        10          4
        20          4
        30          3
SQL> select min(gra) from 
(select deptno, grade gra from  ( select deptno, avg(sal) avg_sal from emp group by deptno ) 
join salgrade on (avg_sal between losal and hisal));//求部门平均薪水等级的最小值


  MIN(GRA)
----------
         3
SQL> select deptno from (select deptno, grade gra from  ( select deptno, avg(sal
) avg_sal from emp group by deptno ) join salgrade on (avg_sal between losal and
 hisal)) where gra = (select min(gra) from (select deptno, grade gra from  ( sel
ect deptno, avg(sal) avg_sal from emp group by deptno ) join salgrade on (avg_sa
l between losal and hisal)));//求平均薪水等级最低的部门的部门编号


    DEPTNO
----------
        30
SQL> select dname from dept where deptno = 
(
select deptno from 
(
select deptno, grade gra from  
( 
select deptno, avg(sal) avg_sal from emp group by deptno 
) 
join salgrade on (avg_sal between losal and hisal)
) 
where gra = 
(
select min(gra) from 
(
select deptno, grade gra from  
( 
select deptno, avg(sal) avg_sal from emp group by deptno 
) 
join salgrade on (avg_sal between losal and hisal)
)
)
);//求平均薪水等级最低的部门的部门名称


DNAME
--------------
SALES


创建视图
SQL> create view v$_dept_avg_sal_info as
  2  select deptno, grade gra from  ( select deptno, avg(sal) avg_sal from emp g
roup by deptno ) join salgrade on (avg_sal between losal and hisal);


SQL> select dname from dept where deptno = 
(
select deptno from 
(
v$_dept_avg_sal_info
) 
where gra = 
(
select min(gra) from 
(
v$_dept_avg_sal_info
)
)
);//求平均薪水等级最低的部门的部门名称






----求部门经理平均薪水最低的部门名称
SQL> select distinct e1.ename, e1.deptno, e1.sal from emp e1 join emp e2 on (e2.
mgr = e1.empno);//求出所以经理的部门编号和薪水


SQL> select deptno, avg(sal) avg_sal from (select distinct e1.ename, e1.deptno,
e1.sal from emp e1 join emp e2 on (e2.mgr = e1.empno)) group by deptno;//求出各部门经理的平均薪水


SQL> create view v$_dept_mgr_avg_sal as
  2  select deptno, avg(sal) avg_sal from (select distinct e1.ename, e1.deptno,e1.sal 
from emp e1 join emp e2 on (e2.mgr = e1.empno)) group by deptno;//创建视图


SQL> select min(avg_sal) from v$_dept_mgr_avg_sal;求出部门经理平均薪水的最小值


SQL> select deptno from v$_dept_mgr_avg_sal where avg_sal = (
  2  select min(avg_sal) from v$_dept_mgr_avg_sal);//部门经理平均薪水最低的部门编号


SQL> select dname from dept join
  2  (select deptno from v$_dept_mgr_avg_sal where avg_sal = (
  3  select min(avg_sal) from v$_dept_mgr_avg_sal))
  4  t on dept.deptno =  t.deptno;//部门经理平均薪水最低的部门名称
 


----求薪水比普通雇员的最高薪水还要高的部门经理的名字
SQL> select t.ename from (select distinct e1.ename, e1.sal from emp e1 join emp
e2 on (e1.empno = e2.mgr)) t where t.sal > ( select max(sal) from emp where empn
o not in (select distinct mgr from emp where mgr is not null));




----薪水最高的前5名雇员
SQL> select ename, sal from
  2  (select ename, sal from emp order by sal desc) where rownum <= 5;


----求薪水最高的6到10名雇员
SQL> select r, ename, sal from
  2  (select rownum r, ename, sal from
  3  (select ename, sal from emp order by sal desc)) where r >= 6 and r <= 10;