咋们来实战一下

一、先查出表两个表的数据

SELECT * FROM apps t1

SELECT * FROM user t2;

二、left join（左关联）

SELECT * FROM apps t1
LEFT JOIN `user` t2
ON t1.id=t2.id

 三、right join（右关联）

SELECT * FROM apps t1
RIGHT JOIN `user` t2
ON t1.id=t2.id

 四、join（内关联）

SELECT * FROM apps t1
JOIN `user` t2
ON t1.id=t2.id