01.查询员工表所有数据，并说明使用*的缺点
select * from emp
02.查询职位（JOB）为'PRESIDENT'的员工的工资
select sal from emp where job='PRESIDENT'
03.查询佣金（COMM）为0或为NULL的员工信息
select * from emp where COMM=0 or comm=null
04.查询入职日期在1982-5-1到1981-12-31之间的所有员工信息
select * from emp where HIREDATE between to_date('1981-12-31','yyyy-mm-dd') AND to_date('1982-05-01','yyyy-mm-dd')
select * from emp where to_char (HIREDATE,'yyyy-mm-dd') between '1981-12-31' and '1982-05-01'
05.查询所有名字长度为4的员工的员工编号，姓名
select empno,ename from emp where ename like '____'
select empno,ename from emp where length(ename)=4;
06.显示10号部门的所有经理（'MANAGER'）和20号部门的所有职员（'CLERK'）的详细信息
select * from emp where (deptno=10 and job= 'MANAGER') or (deptno=20 job='CLERK')
07.显示姓名中没有'L'字的员工的详细信息或含有'SM'字的员工信息
select * from emp where ename not like '%L%' or ename like '%SM%'
08.显示各个部门经理（'MANAGER'）的工资
select SAL from emp where job='MANAGER'
09.显示佣金（COMM）收入比工资（SAL）高的员工的详细信息
select * from emp where comm > sal
10.把hiredate列看做是员工的生日，求本月过生日的员工（考察知识点：单行函数）
select * from emp where to_char(hiredate,'mm') = to_char(sysdate,'mm')
11.把hiredate列看做是员工的生日，求下月过生日的员工（考察知识点：单行函数）
select * from emp where to_char(hiredate,'mm') = to_char(add_months(sysdate,1),'mm')
12.求1982年入职的员工（考察知识点：单行函数）
select * from emp where to_char(hiredate,'yyyy') > '1982'
13.求1981年下半年入职的员工（考察知识点：单行函数）
select * from emp where to_char(hiredate,'mm') >=6
14.求1981年各个月入职的员工个数（考察知识点：组函数）
select to_char(hiredate,'mm') ,count(*) from emp where to_char(hiredate,'yyyy')='1981' group by to_char(hiredate,'mm')
15.查询各个部门的平均工资
select deptno ,avg(sal) from emp group by deptno
16.显示各种职位的最低工资
select job ,min(sal) from emp group by job;
17.按照入职日期由新到旧排列员工信息
select * from emp order by hiredate desc
18.查询员工的基本信息，附加其上级的姓名(内连接)
select t1.* ,t2.ename 上级 from emp t1 join emp t2 on t1.empno= t2.mgr;
19.显示工资比'ALLEN'高的所有员工的姓名和工资
select ename ,sal from emp where sal> (select sal from emp where ename='ALLEN');
select t1.* from emp t1 join emp t2 on nvl(t1.sal,0)> nvl(t2.sal,0) where t2.ename='ALLEN';
20.显示与'SCOTT'从事相同工作的员工的详细信息
select t1.* from emp t1 join emp t2 on t1.job = t2.job where t2.ename='SCOTT'
21.显示销售部（'SALES'）员工的姓名
select ename from emp e, dept d where e.deptno = d.deptno and d.dname='SALES';
22.显示与30号部门'MARTIN'员工工资相同的员工的姓名和工资
select t1.ename ,t1.sal from emp t1 join emp t2 on t1.sal= t2.sal where t2.ename='MARTIN'
23.查询所有工资高于平均工资的销售人员（'SALESMAN'）
select * from emp where sal > (select nvl(avg(sal),0) from emp)
24.显示所有职员的姓名及其所在部门的名称和工资
select ename ,dname,sal from emp e,dept d where e.deptno=e.deptno
25查询在研发部（'RESEARCH'）工作员工的编号，姓名，工作部门，工作所在地
select empno, ename ,dname , loc from emp e,dept d where e.deptno=e.deptno and dname='RESEARCH'
26.查询各个部门的名称和员工人数
select d.dname,count(*) from emp e,dept d where e.deptno=d.deptno group by d.dname
27.查询 各个职位 员工工资大于平均工资（平均工资包括所有员工）的人数 和员工职位
select count(*) ,job from emp where sal >(select nvl(avg(sal),0) from emp) group by job
28.查询工资相同的员工的工资和姓名 (去重复)
select t1.ename ,t1.sal from emp t1 join emp t2 on t1.sal=t2.sal where t1.empno!=t2.empno
29.查询工资最高的3名员工信息（先排序再选前三个）
select * from emp where empno in ( select empno from ( select empno from emp order by sal desc)t
where rownum<=3);
30.按工资进行排名，排名从1开始，工资相同排名相同（如果两人并列第1则没有第2名，从第3名继续排）
select e.*,(select count(*) from emp where sal>e.sal)+1 rank from emp e order by rank;
31.求入职日期相同的（年月日相同）的员工
select t1.* from emp t1 join emp t2 on to_char(t1.hiredate,'yyyy-mm-dd')= to_char(t2.hiredate,'yyyy-mm-dd') where t1.empno != t2.empno;
32.查询每个部门的最高工资
select deptno,max(sal) from emp group by deptno order by deptno;
33.查询每个部门，每种职位的最高工资
select deptno,job,max(sal) from emp group by deptno,job order by deptno,job;
34.查询每个部门有多少人
select deptno,count(*) from emp group by deptno;