请教一个SQL查询语句写法 - V2EX

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请教一个SQL查询语句写法

brikhoff 2013-09-22 16:26:05 +08:00 2535 次点击

这是一个创建于 4402 天前的主题，其中的信息可能已经有所发展或是发生改变。

类似与新浪微博共同关注的人。多对多的问题。关注表id uid fid：id主键，uid用户uid(被关注者), fid粉丝uid(关注者)。现在有a,b两个人其uid分别为1和2，那么如何查询其共同关注的人。"SELECT * FROM `u_f` WHERE fid = 2 and uid in (SELECT uid FROM `u_f` WHERE fid = 1)"，这条语句是可以得到，但是如果是要查询三个人共同关注的呢，要查询四个人共同关注的呢，如果这样上上面那样嵌套感觉有点并不靠谱，还是本身表结构上面就有问题？

1 条回复 1970-01-01 08:00:00 +08:00

1

rpx

2013-09-22 16:42:11 +08:00

1

我的思路：
先分别查出关注者1 2 3 4所关注的对象id，（4句单独sql可以实现）
然后把这4个sql的结果当成表，直接join就可以了。

或者
select uid,count(*)
from u_f
where fid in (1,2,3,4)
group by uid
having count(*)=4 --几个人就等于几
注意性能

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