相互朋友 - SQL算法

Question

我想要找到共同的朋友。

我有一個像這樣結構的表：

 `friends` (   
    `inviter`  int(11) NOT NULL,   
    `accepter`  int(11) NOT NULL,   
    `time` datetime NOT NULL,)
ENGINE=InnoDB DEFAULT CHARSET=utf8 COLLATE=utf8_turkish_ci;

我的load_my_friends(##MY ID##); 查詢是這樣的：

SELECT  p.id , p.name,p.lastname,p.thumb
FROM  friends AS f
RIGHT JOIN  profiles AS p ON ( f.accepter = p.id OR f.inviter = p.id ) 
WHERE  f.inviter = ##MY ID##
OR  f.accepter = ##MY ID##
LIMIT 0 , 5000

你能告訴我如何獲取共同的朋友數據嗎？

注意：我沒有使用任何社交網絡腳本，如JCOW，社交引擎等。

---

編輯@ 2

在數據庫中，我有user1，user2，user3，user4，user5..userX

• user1的朋友是：2,3,6,7,8
• user2的朋友是：1,3,4,5,7,8

我想要一個可以獲取這些結果的查詢：

     | id  | name |lastname| thumb
    1|  3  |raheel|shan    | /img01.jpg
    2|  7  | arqu |x       | /img02.jpg
    3|  8  |abcdef|hijklmno| /img06.jpg

Answer 1

一個可能很容易理解的查詢如下：

SELECT p.* 
FROM 
    (
       -- all friends of User A
       SELECT accepter AS friend_id FROM friends WHERE inviter IN (##User_A_ID##)
       UNION
       SELECT inviter AS friend_id FROM friends WHERE accepter IN (##User_A_ID##)
    ) AS t1
    -- intersect with
    JOIN
    (
       -- all friends of User B
       SELECT accepter AS friend_id FROM friends WHERE inviter IN (##User_B_ID##)
       UNION
       SELECT inviter AS friend_id FROM friends WHERE accepter IN (##User_B_ID##)
    ) AS t2
    ON t1.friend_id = t2.friend_id

    JOIN profiles p on p.id=t1.friend_id

Answer 2

也許有人可以想出一個更簡單的方法來做到這一點，但這是我的理由：

SELECT id,name,lastname FROM profiles, 
  (SELECT *
   FROM friends 
   WHERE  
       (inviter = 1 OR accepter = 1) 
       AND (accepter IN ( 
             SELECT inviter 
             FROM   friends 
             WHERE  accepter = 2 AND inviter != 1)
          OR accepter IN ( 
             SELECT accepter 
             FROM   friends 
             WHERE  inviter = 2 AND accepter != 1)
          OR inviter IN ( 
             SELECT inviter 
             FROM   friends 
             WHERE  accepter = 2 AND inviter != 1)
          OR inviter IN (
             SELECT accepter
             FROM   friends 
             WHERE  inviter = 2 AND accepter != 1)))
    f
    WHERE id != 1 AND (inviter = id OR accepter = id);

其中user1的id = 1，user2的id = 2

看看 - http://sqlfiddle.com/#!2/15951/8

Answer 3

如果您只是想要在兩個用戶（User_A和User_B）之間共享的朋友列表，那么這可能就足夠了：

SELECT accepter 
FROM   friends 
WHERE  inviter = ##User_A_ID## 
       AND accepter IN ( 
          SELECT accepter 
          FROM   friends 
          WHERE  inviter = ##User_B_ID## )

加入您的個人資料表以獲取其他相關數據。

Answer 4

SELECT * 
FROM profiles p
WHERE p.id IN (
    SELECT f_id 
    FROM (
        SELECT accepter as f_id FROM friends where inviter IN (1,2)
        UNION
        SELECT inviter as f_id FROM friends where accepter IN (1,2)
    ) friends 
    GROUP BY f_id
    HAVING count(*) > 1
)

假設友誼是獨特的行....