Postgresql根据共同好友的数量来选择你可能认识的人 - Postgresql select people you may know orderded by number of mutual friends

我正在建立一个社交网络，我希望我的会员能够轻松地找到新朋友。就像在Facebook上一样，我想向他们推荐一些他们可能通过共同朋友的数量认识的人。

我的PostgreSQL友谊数据库结构如下：

> PROFILES_FRIENDSHIPS
> ----------------------
> - fri_profile_from // int, Person who sent the friendship request
> - fri_profile_to // int, Person who received the friendship request
> - fri_accepted // tinyint, has the person accepted the friendship request?

这是我在PostgreSQL中发现的查询，用于查找2个配置文件(ID为24的配置文件和ID为26的配置文件(之间的共同好友数量：

SELECT COUNT(*)
FROM profiles AS p
INNER JOIN (
        SELECT (
        CASE    WHEN ( 26 = f.fri_profile_from ) THEN f.fri_profile_to 
                    ELSE f.fri_profile_from END) AS fri_profile_from 
        FROM profiles_friendships AS f 
        WHERE 1 = 1
        AND (f.fri_profile_to = 26 OR f.fri_profile_from = 26) 
        AND fri_accepted = 1) 
AS f1 
ON (f1.fri_profile_from = p.pro_id) 
INNER JOIN (
        SELECT (
        CASE    WHEN ( 24 = f.fri_profile_from ) THEN f.fri_profile_to 
                    ELSE f.fri_profile_from END) AS fri_profile_from 
        FROM profiles_friendships AS f 
        WHERE 1 = 1
        AND (f.fri_profile_to = 24 OR f.fri_profile_from = 24) 
        AND fri_accepted = 1) 
AS f2 
ON (f2.fri_profile_from = p.pro_id)

现在我一直在尝试转换这个查询，让它找到我最共同的朋友的个人资料，但他们不是我的朋友。但没有成功。。。我也在这个网站上研究了很多例子，但大多数都是在友谊表中使用双重记录。就像如果24是26的朋友一样，有两个记录：(24，26(和(26，24(。这使他们更容易加入并找到共同的朋友，但这不是我想要建立数据库的方式。

如果有人能帮我开始这个问题，我将非常感激。

WITH friends AS(
  SELECT p.pro_id, CASE WHEN f.fri_profile_from = p.pro_id THEN f.fri_profile_to 
                    ELSE f.fri_profile_from END AS friend_id
  FROM profiles
)
SELECT f2.pro_id, count(*) as friend_count
FROM friends AS f1
  JOIN friends AS f2
    ON f1.friend_id=f2.friend_id
       AND f1.pro_id != f2.pro_id
       AND f1.pro_id != f2.friend_id
WHERE f1.pro_id = :user_id
GROUP BY f2.pro_id
ORDER BY friend_count;

步骤1让所有不是朋友的

Select * 
From profiles
where (from/to_friendship is not myID)

步骤2包括一个列有#共同的朋友和订单通过它

select *, 
  (select count(*) from [mutual friends query]) as NrOfMutualFriends)
From profiles
where (from/to_friendship is not myID)
Order by NrOfMutualFriends

编辑：共同好友查询：

步骤1选择我的所有朋友和他的所有朋友

select if(from = myId, to, from) as myfriendids
from PROFILES_FRIENDSHIPS where from = myid or to = myid
select if(from = hisId, to, from) as hisfriendids
from PROFILES_FRIENDSHIPS where from = hisId or to = hisId

步骤2将这些查询合并为1个

select count(*) 
from 
  ( select if(from = myId, to, from) as myfriendids
    from PROFILES_FRIENDSHIPS where from = myid or to = myid) myfriends
inner join 
  ( select if(from = hisId, to, from) as hisfriendids
  from PROFILES_FRIENDSHIPS where from = hisId or to = hisId) hisfriends
on myfriendsids = hisfriendsids

您可以轻松创建双记录格式的内联视图：

with cte_friends(user_id, friend_id) as (
    select
        fri_profile_from, fri_profile_to
    from PROFILES_FRIENDSHIPS
    where fri_accepted = 1
    union all -- or union if there could be duplicates
    select
        fri_profile_to, fri_profile_from
    from PROFILES_FRIENDSHIPS
    where fri_accepted = 1
)
select
    f2.friend_id, count(distinct f2.user_id)
from cte_friends as f1
    inner join cte_friends as f2 on f2.user_id = f1.friend_id
    left outer join cte_friends as f3 on f3.user_id = f2.friend_id and f3.friend_id = f1.user_id
where
    f1.user_id = 1 and f3.user_id is null and
    f2.friend_id != 1
group by f2.friend_id
order by 2 desc

sql-fiddle演示