MySQL JOIN

2024.6.30

1.INNER JOIN：取交集

 

2024.7.4

1.JOIN等价于INNER JOIN，相同的key匹配上时会产生笛卡尔积！

举个例子

Mysql中表student_table(id,name,birth,sex)，插入如下记录：

('1004' , '张三' ,'2000-08-06' , '男');
('1009' , '李四', '2000-01-01', '男');
('1010' , '李四', '2001-01-01', '男');
('1006' , '王五', '2000-08-06' , '女');
('1008' , '张三', '2002-12-01', '女');
('1012' , '张三', '2001-12-01', '女');
('1011' , '李四', '2002-08-06' , '女');

 

执行

select t1.*,t2.*
from (
select * from student_table where sex = '男' ) t1 
join 
(select * from student_table where sex = '女')t2 
on  t1.name = t2.name ; 

结果是

 

2024.7.9

1.MySQL不支持 FULL JOIN