MySQL问题求助呀各位大神！！！

Question

有三张表：Students表，Friends表和Salary表，请问如何找出朋友工资比自己高的人？

创建三张表的代码如下：

create table Students(
ID int NOT NULL ,
s_name char(10) NOT NULL ,
primary key(ID)
)ENGINE=InnoDB;
create table Friends(
ID int NOT NULL ,
Friend_ID int NOT NULL ,
primary key(ID)
)ENGINE=InnoDB;
create table Salary(
ID int NOT NULL ,
Salaries int NOT NULL ,
primary key(ID)
)ENGINE=InnoDB;

insert into Students(ID,
s_name)
values(1,'甲'),
(2,'乙'),
(3,'丙'),
(4,'丁');
insert into Friends(ID,
Friend_ID)
values(1,2),
(2,3),
(3,4),
(4,1);
insert into Salary(ID,
Salaries)
values(1,2000),
(2,1000),
(3,5000),
(4,500);

Answer 1

SELECT s.ID,sa.Salaries,f.ID,sa2.Salaries
FROM students s
LEFT JOIN Friends f ON s.id = f.Friend_ID
LEFT JOIN Salaries sa on sa.id = s.id
LEFT JOIN Salaries sa2 on f.id = sa2.id
WHERE sa2.Salaries < sa.Salaries

你试一下看看是不是要的结果