Oracle查询练手1

表结构

员工表

emp表结构如下：

Name	Type	Nullable	Default	Comments
EMPNO	NUMBER(4)			员工号
ENAME	VARCHAR2(10)	Y		员工姓名
JOB	VARCHAR2(9)	Y		工作
MGR	NUMBER(4)	Y		上级编号
HIREDATE	DATE	Y		雇佣日期
SAL	NUMBER(7,2)	Y		薪金
COMM	NUMBER(7,2)	Y		佣金
DEPTNO	NUMBER(2)	Y		部门编号

部门表

dept表结构如下：

Name	Type	Nullable	Default	Comments
DEPTNO	NUMBER(2)			部门编号
DNAME	VARCHAR2(14)	Y		部门名称
LOC	VARCHAR2(13)	Y		地点

提示：工资 = 薪金 + 佣金

问题

1.列出至少有一个员工的所有部门

--第一种
select dname from dept where deptno in (select deptno from emp);
--第二种
select dname from dept where deptno in (select deptno from emp group by deptno having count(deptno) >=1);
--第三种
select dname from dept a where exists (select deptno from emp b where b.deptno = a.deptno );

2.列出薪金比“SMITH”多的所有员工

--第一种
select * from emp where sal > (select sal from emp where ename = 'SMITH');
--第二种
select * from emp a,(select sal from emp where ename = 'SMITH') b where a.sal > b.sal ;
--第三种
select * from emp a where exists (select null from emp b where a.sal>b.sal and b.ename = 'SMITH');

3.列出所有员工的姓名及其直接上级的姓名

--第一种
select a.ename,b.ename as boos_name from emp a left join emp b on a.mgr = b.empno;
--第二种
select a.ename,(select ename from emp b where b.empno = a.mgr) as boos_name from emp a;

4.列出受雇日期早于其上级的所有员工

--第一种
select a.* from emp a inner join emp b on b.empno = a.mgr where a.hiredate<b.hiredate;
--第二种
select a.* from emp a where exists (select null from emp b where b.empno = a.mgr and a.hiredate<b.hiredate);

5.列出部门名称和这些部门的员工信息，同时列出那些没有员工的部门

--第一种
select a.dname,deptno,b.empno,b.ename,b.job,b.mgr,b.hiredate,b.sal,b.comm from dept a left join emp b using(deptno);
--第二种
select a.dname,b.* from dept a left join emp b on b.deptno = a.deptno;

6.列出所有“CLERK"（办事员）的姓名及其部门名称

--第一种
select a.ename,b.dname from emp a left join dept b on b.deptno=a.deptno where a.job='CLERK';
--第二种
select dname,ename from (select ename,deptno from emp where job= 'CLERK') left join dept using(deptno);

7.列出最低薪金大于1500的各种工作

--第一种
select job from emp group by job having min(sal)>1500;
--第二种
select distinct job from emp a where a.sal>1500 and not exists(select null from emp b where a.job = b.job and a.sal>b.sal);

8.列出在部门“SALES"（销售部）工作的员工的姓名，假定不知道销售部的部门编号

--第一种
select ename from emp a inner join dept b on a.deptno = b.deptno and b.dname='SALES';
--第二种
select ename from emp a where a.deptno = (select deptno from dept where dname = 'SALES');
--第三种
select ename from emp a where exists (select null from dept b where a.deptno = b.deptno and b.dname='SALES');

9.列出薪金高于公司平均薪金的所有员工

select * from emp where sal > (select avg(sal) from emp );  

10.列出与“SCOTT”从事相同工作的所有员工

--第一种
select * from emp where job =(select job from emp where ename='SCOTT');
--第二种
select * from emp a where exists (select null from emp b where a.job=b.job and b.ename='SCOTT');

11.列出薪金等于部门编号为30中员工的薪金的所有员工的姓名和薪金

--第一种
select a.ename,a.sal from emp a where a.deptno <> 30 and exists (select null from emp b where b.deptno=30 and a.sal=b.sal);
--第二种
select a.ename,a.sal from emp a where a.sal in (select sal from emp where deptno=30) and a.deptno<> 30;

12.列出薪金高于在部门编号为30工作的所有员工的薪金的员工姓名和薪金

select ename,sal from emp where sal>(select max(sal) from emp where deptno=30);

13.列出在每个部门工作的员工数量、平均薪金

select (select b.dname from dept b where b.deptno=a.deptno) as dname,count(deptno) as deptcount,avg(sal) as deptavgsal from emp a group by deptno;

14.列出所有员工的姓名、部门名称和工资（工资 = 薪金 + 佣金）

select a.ename,b.dname,a.sal+nvl2(a.comm,a.comm,0) as wage from emp a left join dept b on a.deptno= b.deptno;

15.列出所有部门的详细信息和部门人数

--第一种
select a.*,(select count(deptno) from emp b where b.deptno = a.deptno group by b.deptno) as count from dept a;
--第二种
select deptno,DNAME,LOC,coalesce(emp_count,0) from dept  left join (select count(deptno) emp_count,deptno from emp b group by b.deptno) a using(deptno);

16.列出各种工作的最低工资

--第一种
select job,min(sal) from emp group by job;
--第二种
select distinct job,sal from emp a where not exists(select null from emp b where a.job=b.job and a.sal>b.sal);

17.列出各个部门的MANAGER(经理)的最低薪金

--第一种
select a.deptno,min(sal) from emp a where a.job='MANAGER' group by a.deptno;

18.列出所有员工的年工资，按年薪从低到高排序

--第一种
select ename,(sal+nvl(comm,0))*12 as salpersal from emp order by salpersal
--第二种
select ename,(sal+coalesce(comm,0))*12 as salpersal from emp order by 2;

19.用一条SQL语句查询出emp表中每个部门工资前三位的数据，显示结果如下：

DEPTNO	SAL1	SAL2	SAL3
10	5500	5500	5500
20	4000	3000	2975
30	2850	1600	1500

select deptno, max(sal) sal1, max(decode(id, 2, sal)) sal2, min(sal) sal3
  from (select sal, deptno, id
          from (select ename,
                       sal,
                       ROW_NUMBER() over(partition by deptno order by sal desc) id,
                       deptno
                  from emp) e
         where e.id <= 3)
 group by deptno;