java开发常见笔试题(数据库篇)

一.根据下列员工信息表和部门信息表完成以下SQL查询

(表1 emp_xiangyoulu 员工信息表)

(表2 dept_xiangyoulu)

1.查询所有员工信息

Select * from emp_xianyoulu;

2.查看所有部门信息

Select * from dept_xiangyoulu;

3:查看公司工资排名的第2-5名(分页查询rownum )

select * from(

select rownum rn,ename,sal from emp_xiangyoulu order by sal desc) where rn between 2 and 5;--->错! 伪列rownum和排序order by 同时出现时,先生成伪列号,再按条件排序--->导致rn对应的序号在排序之前就定了,查出的结果和预期不符;;

SELECT ROWNUM rn,e.* FROM (

SELECT * FROM emp_xiangyoulu ORDER BY sal desc) e

WHERE rn BETWEEN 2 AND 5;--->错! "RN": 标识符无效,伪列号不能直接当成一般属性直接用;

select rownum,e.* from(

select * from emp_xiangyoulu order by sal desc)e

where rownum between 2 and 5;--->错! 不报错,但查询结果为0条,原因同上;

select * from(

select rownum,e.* from(

select * from emp_xiangyoulu order by sal desc)e)

where rownum between 2 and 5;--->错! 不报错,但查询结果为0条,rownum 没取别名,直接用有影响;

select * from(

select rownum rn,e.* from(

select * from emp_xiangyoulu order by sal desc)e)

where rn between 2 and 5;--->结果正确!!!

:查看奖金为NULL的员工

select * from emp_xiangyoulu where comm is null;(不能用=,=只能判断是否为" "空字符串)

4.数据库中出现两条一样的数据,如何只留一条

DISTINCT关键字(distinct)去重;

在SELECT子句中使用，用来对指定的字段值去除重复行。

查看公司有哪些职位

SELECT DISTINCT job FROM emp;

多字段去重时，不保证单一的某个字段的值没有重复，而去重原则是这些字段值的

组合没有重复行。

SELECT DISTINCT job,deptno FROM emp

删除除了ID之外,其他都一样的冗余数据(重复数据只保留一条);

delete student where (code,name) in(

select code,name from student group by code,name having

count(name)>1)

and id not in(

select min(id) from student group by code,name having

count(name)>1);

delete student where id not in(

select min(id) from student group by code,name);

select * from student;

5.查询最低薪水高于30号部门最低工资的部门信息

SELECT deptno, MIN(sal) min_sal FROM emp

GROUP BY deptno

HAVING min_sal >(SELECT MIN(sal)

FROM emp WHERE deptno = 30);

询部门平均薪资大于2000的所有员工信息;

select * from emp where deptno in (

select deptno from emp group by deptno

hiving AVG(sal)>2000

);

9.查询每个部门每种职位的员工人数;

Select count(job),deptno,job

from emp_xiangyoulu

group by rollup(deptno,job);

10:查看从2008-08-08号到今天为止一共经历了多少天

SELECT SYSDATE-TO_DATE('2008-08-08','YYYY-MM-DD')

FROM DUAL;

--向上取整；；

--SELECT CEIL(SYSDATE-TO_DATE('2008-08-08','YYYY-MM-DD'))

FROM DUAL;

11:将每名员工入职时间以例如:(1981年12月3日的形式显示)

select ename,to_char(hiredate, 'yyyy"年"MM"月"dd"日"')

from emp_xiangyoulu;

12:查看SMITH的上司在哪个城市工作(三表关联查询)

Select ,,,,

from emp_xiangyoulu e,emp_xiangyoulu m,dept_xiangyoulu d

Where = and = and ='smith';

13:查看平均工资高于2000的那些部门名字以及所在城市

select ,avg,, from emp_xiangyoulu e,dept_xiangyoulu d

where = group by ,, having avg>2000;

14.在NEW YORK工作的员工有多少人

select count, from emp_xiangyoulu e,dept_xiangyoulu d

where = and ='NEW YORK' group by ;

15:查看低于自己所在部门平均工资的员工(将查询结果作为表来关联查

询 )

select ,, from emp_xiangyoulu e,(

select avg(sal) a_sal,deptno from emp_xiangyoulu group by deptno) d where = and < ;