sql中join与left-join图解区别

t1表内容如下：

t2表内容如下：

下面来简述join和left join/right join的区别：

inner join

select * from t1 inner join t2 on t1.id = t2.id;

公共部分的数据才会被查询出来；

left join

select * from t1 left join t2 on t1.id = t2.id;

查询出来的结果和前表记录数一样多；

right join

select * from t1 right join t2 on t1.id = t2.id;

能转化为

select * from t2 left join t1 on t1.id = t2.id;