Oracle select 笔记

emp , dept 均为Oracle内置表

--授权语句

conn sys/12346 as sysdba; 连接sysdba

grant create table , create view to scott; 授权

--求部门中哪些人的薪水最高

select ename , sal from emp

join (select max(sal) max_sal , deptno from emp group by deptno) t

on (emp.sal = t.max_sal and emp.deptno = t.deptno )

--求部门平均薪水的等级

select deptno , avg_sal , grade from

(select avg(sal) avg_sal , deptno from emp group by deptno) t

join salgrade s on (t.avg_sal between s.losal and s.hisal)

--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

--雇员中有哪些人是经理人

select empno , ename from emp

where empno in (select distinct mgr from emp)

--不准用组函数，求薪水的最高值(面试题)

select sal from emp where sal not in

(select e1.sal from emp e1

join emp e2 on (e1.sal < e2.sal) )

--求平均薪水最高的部门的部门编号

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 from emp group by deptno ) )

--求平均薪水最高的部门的部门名称

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 from emp group by deptno ) )

)

--求平均薪水的等级最低的部门的部门名称

第一种方法

select t1.deptno , dname , avg_sal , grade from

(

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)

)

)t1

join dept d on (d.deptno = t1.deptno)

where t1.grade =

(

select min(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)

)

第二种方法 创建视图

conn sys/12346 as sysdba; 连接sysdba

grant create table , create view to scott; 授权

create view v$_dept_avg_sal_info as

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);

select dname , t1.deptno , avg_sal , grade from

v$_dept_avg_sal_info t1

join dept d on (d.deptno = t1.deptno)

where t1.grade =

(

select min(grade) from v$_dept_avg_sal_info

);

--求部门经理人中平均薪水最低的部门名称

--求比普通员工的最高薪水还要高的经理人名称

第一种方法

select ename from emp

where empno in (select distinct mgr from emp where mgr is not null)

and

sal >

(

select max(sal) from emp where empno not in

(select distinct mgr from emp where mgr is not null )

)

第二种方法

select mgr , sal ,ename from emp

join

(select max(sal) max_sal from emp where empno not in

(select distinct mgr from emp where mgr is not null))t

on (t.max_sal < emp.sal)

--求薪水最高的前5名雇员

select ename , sal , rownum from

(

select ename , sal from emp order by sal desc

)

where rownum <= 5

--求薪水最高的第6到第10名雇员(重点掌握)

select ename , sal , r from

(

select ename , sal , rownum r from

( select ename , sal from emp order by sal desc )

)

where r >= 6 and r <= 10

--练习 : 求最后入职的5名员工

select ename , to_char(hiredate , 'YYYY-MM-DD HH24:MI:SS') from

(

select ename , hiredate from emp order by hiredate desc

)

where rownum <= 5

--面试题 : 比较效率

select * from emp where deptno = 10 and ename like '%A%';

select * from emp where ename like '%A%' and deptno = 10;

(理论上上面的语句比下面的语句效率高，但实际当中不一定，如果Oracle对语句

做了优化的话，就可能会把第二条语句中的deptno = 10提到ename前面)