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

1 create table WCEmploy(2     id int AUTO_INCREMENT PRIMARY KEY,3     `name` char(8) not null,4     department_name char(16),5     type char(8),6     salary double7 )

二.插入数据

1 insert into wcemploy values(null,'张三','车间一','钳工',6000)2 insert into wcemploy values(null,'李四','车间一','电工',8000)3 insert into wcemploy values(null,'王五','车间二','车间主任',10000)

1 insert into wcemploy values(null,'泰日天','车间一','钳工',6000),2 (null,'风高放火','车间一','电工',8000),3 (null,'沃尔沃','车间二','车间主任',10000),4 (null,'CVBS','车间二','钳工',2000),5 (null,'单个人','车间三','钳工',4500),6 (null,'人头狗','车间二','钳工',6000),7 (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 wcemployGROUP 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 wcemploywhere 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 wcemploywhere type='钳工' GROUP BY department_nameHAVING AVG(salary)>2000

 

错误写法：

select department_name ,AVG(salary)as avgsalary from wcemploywhere type='钳工'  and AVG(salary)>2000GROUP 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 * fromwcemploy w ,(select AVG(salary) as davg,department_name//一个W表from wcemployGROUP BY department_name)t//一个t表where w.department_name = t.department_name and w.salary

1 select w.*,davg from2 wcemploy w 3 left join (select AVG(salary) as davg,department_name4 from wcemploy5 GROUP BY department_name )t on w.department_name = t.department_name6 where w.department_name = t.department_name and w.salary