mysql中的连接查询

有如下两张表：people和stu_peo 。表中的数据如下所示：

                                                          

内连接

1、两个表之间逗号的作用相当于一个inner join。

select people.Id,people.Name,stu_peo.Id,stu_peo.Namefrom people,stu_peowhere people.Name = stu_peo.Name

2、inner join

select people.Id,people.Name,stu_peo.Id,stu_peo.Namefrom people inner join stu_peo on people.Name = stu_peo.Name

3、只写join默认是inner join

select people.Id,people.Name,stu_peo.Id,stu_peo.Namefrom people join stu_peo on people.Name = stu_peo.Name

外连接

1、left join

select people.Id,people.Name,stu_peo.Id,stu_peo.Namefrom people left join stu_peo on people.Name = stu_peo.Name

left join 是以左表（people）为基础，左表的记录会全部显示出来，而右表（stu_peo）只会显示符合on条件的记录，右表中不符合on条件的记录为显示为Null。

2、right join

select people.Id,people.Name,stu_peo.Id,stu_peo.Namefrom people right join stu_peo on people.Name = stu_peo.Name

right join 是以表右表（stu_peo）为基础，右表的记录会全部显示出来，而左表（people）只会显示符合on条件的记录，左表中不符合on条件的记录为显示为Null。