跟着AI学sql

格鸰爱童话2026-04-14 9:25

1、左连接（返回左表全部） l e f t j o in . . o n . . . .

表1 Person(PersonId,FirstName,LastName)

表2 Address(AddressId,PersonId,City,State)

查询每个人的姓、名、城市、州，没有人的地址也要显示

复制代码

select p.FirstName,p.LastName,a.City,a.State
 from Person p
 left join Address a 
on p.PersonId = a.PersonId;

2、求第二高薪水

表 Employee(id,salary)

复制代码

select salary from Employee 
order by salary desc 
limit 1 offset 1

3、超过经理收入的员工

表Employee(id，name，salary，managerId)

复制代码

select e1.name as Employee from Employee e1 
join Employee e2 
on e1.managerId = e2.id 
where e1.salary > e2.salary

4、查找重复电子邮箱

表Person(id，email)

复制代码

select email from Person group by email 
where having count(emil)>1

5、从不买东西的客户

Customers(id,name), Orders(id,customerId)

复制代码

select name from Customers where 
id not in (select customerId from Orders)
解法2
select c.name as Customers from Customers c 
left join  Orders o 
on c.id=o.customerId 
where o.id is null

6、超过5名学生的课

Courses(studnet,class)

复制代码

select class from Courses group by class 
having count(distinct student) >= 5

注意

where是分组之前过滤，having是分组之后过滤

先where在group by，先groupby在having

复制代码

where->groupby->having