Question

我有一个令我困惑的MySQL查询。我试图从两个不同的表（模糊和用户）中获取特定信息，同时将其限制为仅关注的人。

我有以下查询：

SELECT DISTINCT blurbs.text, blurbs.timestamp, users.name, 
     users.username, users.profilepic, users.id 
FROM blurbs,users 
LEFT OUTER JOIN follows 
ON blurbs.uid = follows.following AND follows.follower = ? 
WHERE (blurbs.uid = $user_id OR follows.following IS NOT NULL) 
     AND (LOWER(blurbs.text) LIKE '%$query%' OR LOWER(users.name) LIKE '%$query%') 
     AND blurbs.is_private=0 AND blurbs.uid=users.id 
LIMIT 0,30

它没有正常工作，但由于连接，我变得过于困惑。

我应该怎么做才能解决这个问题？

Answer 1

尝试通过where子句仅使用所有连接条件，例如

      select a.*, b.*     //<-- Selectign data from first two tables
      from table1 a, table2 b, table1 c
       where a.id = b.id         //<-- joining condition for first two tables
       and a.xxx= c.yyyyy        //some relation with third table
       and c.aaa =....           //filter conditions using third table
       and c.bbb =...            //filter conditions using third table

尝试按以下方式对您的查询进行修改：

   SELECT DISTINCT blurbs.text, blurbs.timestamp, users.name, 
       users.username, users.profilepic, users.id 
   FROM blurbs,users, follows
   WHERE blurbs.uid=users.id
     AND blurbs.uid = follows.following 
     AND follows.follower = ?
     AND (blurbs.uid = $user_id OR follows.following IS NOT NULL) 
     AND (LOWER(blurbs.text) LIKE '%$query%' OR LOWER(users.name) LIKE '%$query%') 
     AND blurbs.is_private=0
   LIMIT 0,30

完成此操作后，我希望您能更好地控制/管理所需的过滤条件。

Answer 2

虽然我不完全确定这是否正是您正在寻找的，但让我根据我对您的问题的理解来解释我的所作所为。首先，在模糊和用户之间进行INNER JOIN而不是交叉连接，假设有一个用户进行模糊处理此外，既然你说你只想把它限制在跟随者，我想你可以用INNER JOIN替换LEFT OUTER来帮助过滤掉非跟随者。

SELECT DISTINCT 
     blurbs.text, 
     blurbs.timestamp, 
     users.name, 
     users.username, 
     users.profilepic, 
     users.id 
FROM blurbs 
INNER JOIN users 
     ON blurbs.uid = users.id 
INNER JOIN follows 
     ON blurbs.uid = follows.following 
     AND follows.follower = users.id 
WHERE blurbs.uid = $user_id 
     AND (LOWER(blurbs.text) LIKE '%$query%' OR LOWER(users.name) LIKE '%$query%') 
     AND blurbs.is_private=0 
LIMIT 0,30

从两个表中选择单个值，同时从第三个表中获取条件

2 个答案: