SQL语法——Join详解

一、INNER JOIN

用法：

select column_name(s)
from table 1
INNER JOIN table 2
ON
table 1.column_name=table 2.column_name

例子：

　两个表：three,user

select* from three inner join user;

select* from three inner join user on three.id = user.id;

二、LEFT JOIN

 用法：

select column_name(s)
from table 1
LEFT JOIN table 2
ON table 1.column_name=table 2.column_name

例子：

select * from three left join user on three.id=user.id;

 三、RIGHT JOIN

 用法：

select column_name(s)
from table 1
RIGHT JOIN table 2
ON table 1.column_name=table 2.column_name

例子：

select * from three right join user on three.id=user.id;

四、FULL OUTER JOIN

用法：

select column_name(s)
from table 1
FULL OUTER JOIN table 2
ON table 1.column_name=table 2.column_name

例子：

select * from three full outer join user on three.id=user.id;

 mysql 报错不支持full join ,但是可以用下面的这种写法取代：

select * from three left outer join user on three.id=user.id union select * from three right outer join user on three.id=user.id；

 参考资料：

https://www.cnblogs.com/reaptomorrow-flydream/p/8145610.html