答案：
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.查询职位(JOB)为'PRESIDENT'的员工的工资
select * from emp where job = 'PRESIDENT';
3.查询佣金(COMM)为0或为NULL的员工信息
select * from emp where comm = 0 or comm is null;
4.查询入职日期在1981-5-1 到1981-12-31之间的所有员工信息
select * from emp where hiredate
between to_date('1981-5-1','yyyy-mm-dd') and to_date('1981-12-31','yyyy-mm-dd');
5.查询所有名字长度为4 的员工的员工编号,姓名
select * from emp where length(ename) = 4;
6.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 and job='CLERK';
7.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%';
8.显示各个部门经理('MANAGER')的工资
select sal from emp where job = 'MANAGER';
9.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
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
12. 求1982年入职的员工
13. 求1981年下半年入职的员工
between to_date('1981-7-1','yyyy-mm-dd') and to_date('1982-1-1','yyyy-mm-dd') - 1;
14. 求1981年各个月入职的的员工个数
select count(*),to_char(trunc(hiredate,'month'),'yyyy-mm')
from emp where to_char(hiredate,'yyyy')='1981'
group by trunc(hiredate,'month')
order by trunc(hiredate,'month');
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
select e.*,e2.ename from emp e,emp e2 where e.mgr = e2.empno;
19. 显示工资比'ALLEN'高的所有员工的姓名和工资
select * from emp where sal > (select sal from emp where ename='ALLEN');
20. 显示与'SCOTT'从事相同工作的员工的详细信息
select * from emp where job = (select * from emp where 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 ename,sal from emp
where sal = (select sal from emp where deptno=30 and ename='MARTIN');
23. 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('SALESMAN')
select * from emp where job='SALESMAN' and sal > (select avg(sal) from emp);
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 = d.deptno and danme='RESEARCH';
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
28. 查询工资相同的员工的工资和姓名
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
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)
31. 求入职日期相同的(年月日相同)的员工
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
33. 查询每个部门,每种职位的最高工资
34. 查询每个员工的信息及工资级别
35. 查询工资最高的第6-10名员工
select * 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
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
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
(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
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
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
where sumsal >(select avg(sum(sal)) from emp group by deptno) and se.deptno =d.deptno;
42. 查询大于各部门总工资的平均值的部门下的员工信息
where sumsal >(select avg(sum(sal)) from emp group by deptno) and se.deptno =e.deptno;
43. 查询没有员工的部门信息
select d.* from dept d left join emp e on (e.deptno = d.deptno) where empno is null;
44. 查询当前月有多少天
select trunc(add_months(sysdate,'month') - trunc(sysdate,'month') from dual;
45. 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
SELECT job,COUNT(empno)
FROM emp
GROUP BY job HAVING MIN(sal)>1500 ;
46. 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
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 ;
47. 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
SELECT e.ename,e.sal,d.dname FROM emp e,51); font-family:Arial; font-size:14px">WHERE sal > ALL (SELECT sal FROM emp WHERE deptno=30) AND e.deptno=d.deptno;
48. 列出所有部门的详细信息和部门人数
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 ;
49. 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
WHERE job<>'SALESMAN'
GROUP BY job HAVING sum>5000
ORDER BY sum ;
50. 客户表a(idnameaddress)登陆流水表b(idtime)购物流水表c(idtimeproductidproductnum)
1.求每个客户的最新登陆时间time,姓名name,客户id?
selecta.id,a.name,d.timeastime
fromaleftjoin(selectid,max(time)astimefrombgroupbyid)d
ona.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)
