Question

我有用户表和 user_followings 表。表格的基本结构如下：

users: id, name, email
users_followings: following_user_id, follower_user_id

follower_user_id是关注其他人的人。
following_user_id是被其他人跟踪的人人

我希望可以点击特定用户查看所有信息，例如谁跟随他/她以及他/她正在跟随的人。

SELECT 
      users.id, 
      users.name, 
      users.email 
                 from users
                 JOIN user_followings ON 
                                      user_followings.follower_user_id = users.id
                 WHERE user_followings.following_user_id = 1

此查询基本上连接两个表并获取所需的结果。

现在假设一个名为“A”的用户已登录，他正在查看用户X的个人资料。有许多人关注了用户X.

让我们说John，Mike，Rusev，Jack等

如何编写一个查询，告诉用户'A'是否跟随John，Mike，Rusev，Jack等跟随上面的查询。

因此，用户A应该能够知道他是否关注John，Mike，Rusev，Jack等

Answer 1

我的理解是OP希望看到用户跟随当前用户（A）的用户A正在查看（X）

在我的例子中，A是id = 1，X是id = 6

SELECT fu.id, fu.name, fu.email
FROM users u
JOIN users_followings f ON f.userId = u.id
JOIN users fu on fu.id = f.follower
WHERE f.userId = 1 
AND f.follower IN (SELECT follower 
                   FROM users_followings 
                   WHERE userId = 6)

我将follower_user_id更改为关注者，将following_user_id更改为userId以免混淆自己

Answer 2

假设id = 1的用户正在查看id = 2的用户的详细信息，并且您希望id = 1的用户知道id = 2的用户的以下或关注者是否与具有id的用户相关以任何方式= 1。试试这个：

SELECT C.*, 
(SELECT 1 FROM user_followings D WHERE D.following_user_id=1 AND 
  C.id=D.follower_user_id LIMIT 1) flwx_viewing_user,
(SELECT 1 FROM user_followings E WHERE E.follower_user_id=1 AND  
  C.id=E.following_user_id LIMIT 1) viewing_user_flwx
FROM
(SELECT A.id, A.name, A.email, 'following' relation 
FROM users 
WHERE EXIST (SELECT 1 
             FROM user_followings B 
             WHERE B.following_user_id=2)
UNION ALL
SELECT A.id, A.name, A.email, 'followers' relation 
FROM users 
WHERE EXIST (SELECT 1 
             FROM user_followings B 
             WHERE B.follower_user_id=2)) C;

Answer 3

我不确定我是否正确但是A的ID = 1而X的ID = 5。如果后面跟着A

，则此查询将为每个跟在X后面的用户返回信息

SELECT
  *,
  CASE WHEN exists(
      SELECT *
      FROM following AFOLLOW
      WHERE AFOLLOW.follower_user_id = 1
            AND XFOLLOWED.follower_user_id = AFOLLOW.following_user_id)
    THEN 'FOLLOWING'
  ELSE 'NOTFOLLOWING' END
FROM following XFOLLOWED
WHERE following_user_id = 5
      AND follower_user_id <> 1;

两个表和连接和左连接在一起

3 个答案: