多表关联查询

两表关联查询的sql语句，咱们会发现限制条件不一样是，查询出来的结果是不同的。

1.下面我们使用左链接查询：

select a.id,a.articlename,a.articledes,a.listimg,a.author,a.click,b.userid from yxdj_post as a left join yxdj_postfavorite as b on a.id=b.articlecode and b.userid='$userid' where a.`status`=1 order by $sort $order limit $offset,$pagesize

当咱们设置$userid变量为1041288时，咱们将会看到以下结果：

2.去掉左连接（left）查询:

select a.id,a.articlename,a.articledes,a.listimg,a.author,a.click,b.userid from yxdj_post as a join yxdj_postfavorite as b on a.id=b.articlecode and b.userid='$userid' where a.`status`=1 order by $sort $order limit $offset,$pagesize

select a.id,a.articlename,a.articledes,a.listimg,a.author,a.click,b.userid from yxdj_post as a left join yxdj_postfavorite as b on a.id=b.articlecode  where a.`status`=1 and b.userid='$userid' order by $sort $order limit $offset,$pagesize

3.若是咱们把限制条件更换一下位置同时也设置$userid变量为1041288时会发现：