フォローしている友達とフォロワーの関係のテーブルを

Question

どのように私は友人のSQLクエリを取得できますか？

私のSql

しかし、私は得ることができないのクエリに続いて共通の友人

id | user_id 
-------------- 
1 | 2 
2 | 3 
3 | 4 
4 | 1 

Relation Table 

id | follower_id | following_id 
-------------------------------- 
1 | 1   | 2 
2 | 2   | 1 
3 | 1   | 4 
4 | 4   | 3 
5 | 4   | 1 

"SELECT `user_id` FROM " . T_USERS . " WHERE `user_id` IN (SELECT `following_id` FROM " . T_FOLLOWERS . " WHERE `follower_id` = {$user_id} AND `following_id` <> {$user_id} AND `active` = '1') AND `active` = '1' "; 

フォロワークエリ

" SELECT `user_id` FROM " . T_USERS . " WHERE `user_id` IN (SELECT `follower_id` FROM " . T_FOLLOWERS . " WHERE `follower_id` <> {$user_id} AND `following_id` = {$user_id} AND `active` = '1') AND `active` = '1'"; 

Answer 1

SELECT `user_id` FROM " . T_USERS . " 
WHERE `user_id` IN (SELECT CASE WHEN `following_id`={$user_id} THEN `follower_id` ELSE `following_id` END user 
         FROM " . T_FOLLOWERS . " 
         WHERE `active` = '1' 
         AND ((`follower_id` = {$user_id} AND `following_id` <> {$user_id}) 
          OR (`follower_id` <> {$user_id} AND `following_id` = {$user_id})) 
         GROUP BY user 
        HAVING count(*)=2 
        ) 
    AND `active` = '1'