[英]Mutual friends sql with join (Mysql)
I have two tables我有两张桌子
users table:用户表:
id|name
user_relationships用户关系
id | user_id | friend_id
and want to get names of mutual friends of 2 users.并想获得 2 个用户的共同朋友的名字。 ie:
IE:
user_relationships
1 | 1 | 3
2 | 2 | 3
users
3| sammy
users 1 and 2 have mutual friend 3. I want to get his name 'sammy' in one query.用户 1 和 2 有共同的朋友 3。我想在一次查询中得到他的名字“sammy”。
How do I do that?我怎么做?
You need to join user_relationships with itself, so that two rows with different user_id
have the same friend_id
您需要将 user_relationships 与自己加入,以便具有不同
user_id
的两行具有相同的friend_id
All mutual friends:所有共同的朋友:
select ur1.user_id user1,
ur2.user_id user2,
ur2.friend_id mutual_friend
from user_relationships ur1
JOIN user_relationships ur2 ON ur1.friend_id = ur2.friend_id
where ur1.user_id != ur2.user_id
Join with users table to get the names:加入用户表以获取名称:
select ur1.user_id user_id1,
u1.name User1,
ur2.user_id user2,
u2.name User2,
ur2.friend_id mutual_friend_id,
u3.name mutual_friend
from user_relationships ur1
JOIN user_relationships ur2 ON ur1.friend_id = ur2.friend_id
JOIN user u1 ON u1.user_id = ur1.user_id
JOIN user u2 ON u1.user_id = ur2.user_id
JOIN user u3 ON ur1.user_id = u3.user_id
where ur1.user_id != ur2.user_id
You can filter for mutual friends for some specific users using ur1.user_id = first_user
and ur2.user_id = second_user
您可以使用
ur1.user_id = first_user
和ur2.user_id = second_user
过滤某些特定用户的共同朋友
SELECT id, name
FROM users
WHERE id IN (
SELECT friend_id
FROM user_relationships
WHERE user_id IN ( 1, 2 )
GROUP BY friend_id
HAVING COUNT(friend_id) >= 2
)
or with one join:或一次加入:
SELECT friend_id, name
FROM user_relationships r
INNER JOIN users u ON r.friend_id = u.id
WHERE user_id IN ( 1, 2 )
GROUP BY friend_id
HAVING COUNT(friend_id) >= 2
You could try something like this:你可以尝试这样的事情:
select id, name from users where id in
(select friend_id from user_relationships where user_id = @user1_id and friend_id in
(select friend_id from user_relationships where user_id = @user2_id)
)
This should return all mutual friends of users with the IDs @user1_id and @user2_id.这应该返回 ID 为 @user1_id 和 @user2_id 的用户的所有共同朋友。 It's not tested yet, but should provide a starting point...
它尚未经过测试,但应该提供一个起点......
didn't check it but this query should give you a list of related user names for ID [no].没有检查它,但这个查询应该给你一个 ID [no] 的相关用户名列表。
select u1.name, u2.name
from users as u1
join user_relationships as ur
on u1.id = ur.user_id
join users as u2
on ur.friend_id = u2.id
where U1.id = [no];
BTW, you don't need an artificial id for your cross-table, as (user_id, friend_id) is already a legitimate primary key.顺便说一句,您的交叉表不需要人工 id,因为 (user_id,friend_id) 已经是合法的主键。
声明:本站的技术帖子网页,遵循CC BY-SA 4.0协议,如果您需要转载,请注明本站网址或者原文地址。任何问题请咨询:yoyou2525@163.com.