Java笔试题之SQL语句（单表）

题目：系统中有一个表WCEmploy(职工号，姓名，部门名，工种，工资)

一.请写出建表语句

create table WCEmploy(
    id int AUTO_INCREMENT PRIMARY KEY,
    `name` char(8) not null,
    department_name char(16),
    type char(8),
    salary double
)

二.插入数据

insert into wcemploy values(null,'张三','车间一','钳工',6000)
insert into wcemploy values(null,'李四','车间一','电工',8000)
insert into wcemploy values(null,'王五','车间二','车间主任',10000)

insert into wcemploy values(null,'泰日天','车间一','钳工',6000),
(null,'风高放火','车间一','电工',8000),
(null,'沃尔沃','车间二','车间主任',10000),
(null,'CVBS','车间二','钳工',2000),
(null,'单个人','车间三','钳工',4500),
(null,'人头狗','车间二','钳工',6000),
(null,'后宫番','车间一','钳工',1500)

多条数据插入

在插入数据的时候，发生了一个错误，插入汉字数据报错

修改MySQL的数据库的数据库属性字符集为

三.查询语句

1.请用一个SQL语句查询每个部门的总人数

select department_name ,COUNT(DISTINCT id) from wcemploy
GROUP BY department_name

2.请用一个SQL语句查询出不同部门的担任“钳工”的职工平均工资

select department_name ,AVG(salary) from wcemploy
where type='钳工'
GROUP BY department_name//如果没有分组，就会出现错误

3.请用一个SQL语句查询出不同部门的担任“钳工”的职工平均工资高于2000的部门

select department_name ,AVG(salary)as avgsalary from wcemploy
where type='钳工' 
GROUP BY department_name
HAVING AVG(salary)>2000

错误写法：

select department_name ,AVG(salary)as avgsalary from wcemploy
where type='钳工'  and AVG(salary)>2000
GROUP BY department_name

4.请用一个SQL语句查询每个部门低于平均工资的员工信息

select * from
wcemploy w ,(select AVG(salary) as davg,department_name//一个W表
from wcemploy
GROUP BY department_name)t//一个t表
where w.department_name = t.department_name and w.salary<davg

select w.*,davg from
wcemploy w 
left join (select AVG(salary) as davg,department_name
from wcemploy
GROUP BY department_name )t on w.department_name = t.department_name
where w.department_name = t.department_name and w.salary<davg