1.查询员工表所有数据, 并说明使用*的缺点
风哥Oracle教程指示：
select * from emp;
使用*的缺点有：查询出了不必要的列；效率上不如直接指定列名。

2.查询大于各部门总工资的平均值的部门下的员工信息
风哥Oracle教程指示：
select e.*,sumsal from emp e, (select sum(sal) sumsal, deptno from emp group bydeptno) se
where sumsal >(select avg(sum(sal)) from emp group by deptno) and se.deptno =e.deptno;

3.查询没有员工的部门信息
风哥Oracle教程指示：
select d.* from dept d left join emp e on (e.deptno = d.deptno) where empno is null;

4.查询当前月有多少天
风哥Oracle教程指示：
select trunc(add_months(sysdate,1),'month') - trunc(sysdate,'month') from dual;

5.列出最低薪金大于1500的各种工作及此从事此工作的全部雇员人数
风哥Oracle教程指示：
SELECT job,COUNT(empno)
FROM emp
GROUP BY job HAVING MIN(sal)>1500 ;

6.列出薪金高于公司平均薪金的所有员工，所在部门，上级领导，公司的工资等级
风哥Oracle教程指示：
SELECT e.empno,e.ename,d.dname,m.ename,s.grade
FROM emp e,dept d,emp m,salgrade s
WHERE sal>(SELECT AVG(sal) FROM emp) AND e.mgr=m.empno AND d.deptno=e.deptno(+)AND e.sal BETWEEN s.losal AND s.hisal ;

7.列出薪金高于在部门30工作的所有员工的薪金的员工姓名和薪金、部门名称
风哥Oracle教程指示：
SELECT e.ename,e.sal,d.dname FROM emp e,dept d
WHERE sal > ALL (SELECT sal FROM emp WHERE deptno=30) AND e.deptno=d.deptno;

8.列出所有部门的详细信息和部门人数
风哥Oracle教程指示：
SELECT d.dname,d.loc,dt.count
FROM dept d,(SELECT deptno,COUNT(*) count FROM emp GROUP BY deptno) dt
WHERE d.deptno=dt.deptno ;

9.显示非销售人员工作名称以及从事同一工作雇员的月工资的总和，并且要满足从事同一工作的雇员的月工资合计大于$5000，输出结果按月工资的合计升序排列
风哥Oracle教程指示：
SELECT job,SUM(sal) sum
FROM emp
WHERE job<>'FGEDU'
GROUP BY job HAVING sum>5000
ORDER BY sum ;

10.把hiredate列看做是员工的生日,求本月过生日的员工
风哥Oracle教程指示：
select * from emp where to_char(hiredate, 'mm') = to_char(sysdate , 'mm');

11.显示销售部('SALES')员工的姓名
风哥Oracle教程指示：
select ename from emp e, dept d where e.deptno = d.deptno and d.dname='SALES';

12.显示与30号部门'ITPUX'员工工资相同的员工的姓名和工资
风哥Oracle教程指示：
select ename, sal from emp
where sal = (select sal from emp where deptno=30 and ename='ITPUX');

13.查询所有工资高于平均工资(平均工资包括所有员工)的销售人员('FGEDU')
风哥Oracle教程指示：
select * from emp where job='FGEDU' and sal > (select avg(sal) from emp);

14.显示所有职员的姓名及其所在部门的名称和工资
风哥Oracle教程指示：
select ename, job, dname from emp e, dept d where e.deptno = d.deptno;

15.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
风哥Oracle教程指示：
select empno,ename,dname,loc from emp e, dept d
where e.deptno = d.deptno and danme='RESEARCH';

16.显示各种职位的最低工资
风哥Oracle教程指示：
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
风哥Oracle教程指示：
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
风哥Oracle教程指示：
select e.*, e2.ename from emp e, emp e2 where e.mgr = e2.empno;

19.显示工资比'fgedu'高的所有员工的姓名和工资
风哥Oracle教程指示：
select * from emp where sal > (select sal from emp where ename='fgedu');

20.显示与'itpux'从事相同工作的员工的详细信息
风哥Oracle教程指示：
select * from emp where job = (select * from emp where ename='itpux');

21.把hiredate列看做是员工的生日,求下月过生日的员工
风哥Oracle教程指示：
select * from emp where to_char(hiredate, 'mm') = to_char(add_months(sysdate,1) ,'mm');

22.求1992年入职的员工
风哥Oracle教程指示：
select * from emp where to_char(hiredate,'yyyy') = '1992';

23.求1991年下半年入职的员工
风哥Oracle教程指示：
select * from emp where hiredate
between to_date('1991-7-1','yyyy-mm-dd') and to_date('1992-1-1','yyyy-mm-dd') - 1;

24.求1991年各个月入职的的员工个数
风哥Oracle学习教程指示：
select count(*), to_char(trunc(hiredate,'month'),'yyyy-mm')
from emp where to_char(hiredate,'yyyy')='1991'
group by trunc(hiredate,'month')
order by trunc(hiredate,'month');

25.查询各个部门的平均工资
风哥Oracle教程指示：
select deptno,avg(sal) from emp group by deptno;

26.查询各个部门的名称和员工人数
风哥Oracle教程指示：
select * from (select count(*) c, deptno from emp group by deptno) e
inner join dept d on e.deptno = d.deptno;

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
风哥Oracle教程指示：
select job, count(*) from emp where sal > (select avg(sal) from emp) group by job;

28.查询工资相同的员工的工资和姓名
风哥Oracle教程指示：
select * from emp e where (select count(*) from emp where sal = e.sal group by sal)> 1;

29.查询工资最高的3名员工信息
风哥Oracle教程指示：
select * from (select * from emp order by sal desc) 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,从第三名继续排)
风哥Oracle教程指示：
select e.*, (select count(*) from emp where sal > e.sal)+1 rank from emp e order byrank;

31.求入职日期相同的(年月日相同)的员工
风哥Oracle教程指示：
select * from emp e where (select count(*) from emp where e.hiredate=hiredate)>1;

32.查询每个部门的最高工资
风哥Oracle教程指示：
select deptno, max(sal) maxsal from emp group by deptno order by deptno;

33.查询每个部门,每种职位的最高工资
风哥Oracle教程指示：
select deptno, job, max(sal) from emp group by deptno, job order by deptno, job;

34.查询每个员工的信息及工资级别
风哥Oracle教程指示：
select e.*, sg.grade from emp e, salgrade sg where sal between losal and hisal;

35.查询工资最高的第6-10名员工
风哥Oracle教程指示：
select * from (select e.*,rownum rn from(select * from emp order by sal desc) e where rownum <=10) where rn > 5;

36.查询各部门工资最高的员工信息
风哥Oracle教程指示：
select * from emp e where e.sal = (select max(sal) from emp where (deptno =e.deptno));

37.查询每个部门工资最高的前2名员工
风哥Oracle教程指示：
select * from emp e where
(select count(*) from emp where sal > e.sal and e.deptno = deptno) < 2
order by deptno, sal desc;

38.查询出有3个以上下属的员工信息
风哥Oracle教程指示：
select * from emp e where
(select count(*) from emp where e.empno = mgr) > 2;

39.查询所有大于本部门平均工资的员工信息
风哥Oracle教程指示：
select * from emp e where sal >
(select avg(sal) from emp where (deptno = e.deptno))
order by deptno;

40.查询平均工资最高的部门信息
风哥Oracle教程指示：
select d.*, avgsal from dept d, (select avg(sal) avgsal, deptno from emp group bydeptno) se
where avgsal = (select max(avg(sal)) from emp group by deptno) and d.deptno =se.deptno;

41.查询大于各部门总工资的平均值的部门信息
风哥Oracle教程指示：
select d.*,sumsal from dept d, (select sum(sal) sumsal, deptno from emp group bydeptno) se
where sumsal >(select avg(sum(sal)) from emp group by deptno) and se.deptno =d.deptno;

42.查询职位(JOB)为'fgedu'的员工的工资
风哥Oracle教程指示：
select * from emp where job = 'fgedu';

43.查询佣金(COMM)为0或为NULL的员工信息
风哥Oracle教程指示:
select * from emp where comm = 0 or comm is null;

44.查询入职日期在1991-5-1 到1991-12-31之间的所有员工信息
风哥Oracle教程指示：
select * from emp where hiredate
between to_date('1991-5-1','yyyy-mm-dd') and to_date('1991-12-31','yyyy-mm-dd');

45.查询所有名字长度为4 的员工的员工编号,姓名
风哥Oracle教程指示：
select * from emp where length(ename) = 4;

46.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
风哥Oracle教程指示：
select * from emp where deptno = 10 and job = 'MANAGER' or deptno = 20 and job='CLERK';

47.显示姓名中没有'L'字的员工的详细信息或含有'fg'字的员工信息
风哥Oracle教程指示：
select * from emp where ename not like '%L%' or ename like '%fg%';

48.客户表a(id name address) 登陆流水表b(id time) 购物流水表c(id time productid productnum)
1.求每个客户的最新登陆时间time,姓名name,客户id?
风哥Oracle教程指示：
select a.id,a.name,d.time as time
from a left join (select id,max(time) as time from b group by id) d
on a.id =d.id ;

2.查最新登陆并且已经购买商品的客户id,name,登陆的时间time(一条sql语句)
风哥Oracle教程指示：
select a.id,a.name,d.time as time
from a,(select id,max(time) as time from b group by id) d
where a.id =d.id
and exists (select * from c where id = a.id);

49.显示各个部门经理('MANAGER')的工资
风哥Oracle教程指示：
select sal from emp where job = 'MANAGER';

50.显示佣金(COMM)收入比工资(SAL)高的员工的详细信息
风哥Oracle教程指示：
select * from emp where comm > sal;