Java筆試題之SQL語句（單表）

題目：系統中有一個表WCEmploy(職工號，姓名，部門名，工種，工資)

一.請寫出建表語句

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

二.插入數據

insert into wcemploy values(null,'張三','車間一','鉗工',6000)
insert into wcemploy values(null,'李四','車間一','電工',8000)
insert into wcemploy values(null,'王五','車間二','車間主任',10000)

insert into wcemploy values(null,'泰日天','車間一','鉗工',6000),
(null,'風高放火','車間一','電工',8000),
(null,'沃爾沃','車間二','車間主任',10000),
(null,'CVBS','車間二','鉗工',2000),
(null,'單個人','車間三','鉗工',4500),
(null,'人頭狗','車間二','鉗工',6000),
(null,'后宮番','車間一','鉗工',1500)

多條數據插入

 

在插入數據的時候，發生了一個錯誤，插入漢字數據報錯

修改MySQL的數據庫的數據庫屬性字符集為

三.查詢語句

1.請用一個SQL語句查詢每個部門的總人數

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

 

2.請用一個SQL語句查詢出不同部門的擔任“鉗工”的職工平均工資

select department_name ,AVG(salary) from wcemploy
where type='鉗工'
GROUP BY department_name//如果沒有分組，就會出現錯誤

3.請用一個SQL語句查詢出不同部門的擔任“鉗工”的職工平均工資高於2000的部門

 

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

 

錯誤寫法：

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

4.請用一個SQL語句查詢每個部門低於平均工資的員工信息

 

select * from
wcemploy w ,(select AVG(salary) as davg,department_name//一個W表
from wcemploy
GROUP BY department_name)t//一個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