18-MySQL-Ubuntu-数据表的查询-连接(七)

students与classes表,两个表的连接字段是students.cls_id=classes.ID

(1) 左连接:left join on

左边表全取,右边表取共有的,没有的为null

select * from students as s left join classes as c on c.ID=s.cls_id

(2) 右连接:right join on

右边表全取,左边表取共有的,没有的为null

select * from students as s right join classes as c on c.ID=s.cls_id;

(3) 内连接:inner join on

两个表取共有的

select * from students inner join classes on students.cls_id=class.ID;