Question

我有3张桌子。

myMembers
------------------------------------
id | username | privacy
------------------------------------
1  | userA    | 0
2  | userB    | 1
3  | userC    | 0
4  | userD    | 1

following
--------------------------------
id  | user_id  | follower_id
--------------------------------
1   | 2        | 1

posts
-------------------------------------
id  |  userID | username   | statusMsg
--------------------------------------
1   |  4      | userD    | Issac Newton is genius
2   |  2      | userB    | Newton Saw apple
3   |  3      | userC    | Newtonian Physics
4   |  1      | userA    | Calculus came from Sir Newton

有一个搜索字段。当登录用户在表“帖子”中搜索“关键字”时，我想省略那些将其隐私设置为“1”且WHERE搜索者没有关注用户B的用户的结果。

查询应该在逻辑上执行此操作。

SELECT * from posts WHERE (match the keyword) 
            AND ( 
                if (poster's privacy (which is set in myMembers)==1){
                    if (seacher is following poster){
                        select this post
                    }
                }
                   else { select this post
                }
             )
                   LIMIT results to 5 rows

因此对于关键字“牛顿”，如果userA正在搜索，则应返回“posts”中的2,3,4行。如果userD正在搜索，则只返回“posts”中的第1,3和4行，

基于隐私和以下内容编辑：标记以备将来搜索：mySql中WHERE子句中的IF条件

Answer 1

请尝试此查询（也在SQL Fiddle上）：

SELECT p.id, p.user_id, m.username, m.privacy,
       searcher.username "Searcher", p.status_msg
  FROM posts p
  JOIN members m ON m.id = p.user_id
  LEFT JOIN following f ON p.user_id = f.user_id
  JOIN members searcher ON searcher.username = 'userA'
 WHERE (m.privacy = 0 OR (m.privacy = 1 AND f.follower_id = searcher.id)
                      OR m.id = searcher.id)
   AND p.status_msg LIKE '%New%'
 ORDER BY p.id
 LIMIT 5;

我从username表中删除了posts字段，因为它是多余的。此外，我将表和列命名略有不同，因此查询可能需要对架构进行外观修改。

WHERE子句中的第一行是您要查找的那一行，它按以下顺序选择帖子：

来自没有隐私的成员的第一篇帖子;
然后发布来自当前searcher;
最后，会员本人的帖子。

修改

此查询使用原始标识符：

SELECT p.id, p.`userID`, m.username, m.privacy, searcher.username "Searcher", p.`statusMsg` FROM posts p JOIN `myMembers` m ON m.id = p.`userID` LEFT JOIN following f ON p.`userID` = f.user_id JOIN `myMembers` searcher ON searcher.username = 'userD' WHERE (m.privacy = 0 OR f.follower_id = searcher.id OR m.id = searcher.id) AND p.`statusMsg` LIKE '%New%' ORDER BY p.id LIMIT 5;

编辑2：

为避免重复，以防来自posts表的用户有多个粉丝，应按以下方式更改加入和过滤条件（在SQL Fiddle上）：

SELECT p.id, p.user_id, m.username, m.privacy, searcher.username "Searcher", p.status_msg FROM posts p JOIN members m ON m.id = p.user_id JOIN members searcher ON searcher.username = 'userC' LEFT JOIN following f ON p.user_id = f.user_id AND follower_id = searcher.id WHERE (m.privacy = 0 OR (m.privacy = 1 AND f.id IS NOT NULL) OR m.id = searcher.id) ORDER BY p.id LIMIT 5;

Answer 2

试试这个：

SELECT a.*
FROM posts a
     LEFT JOIN (SELECT user_id
                FROM following a1
                     INNER JOIN myMembers b1
                       ON a1.follower_id = b1.id
                  WHERE a1.follower_id = 1 AND
                        b1.privacy = 1
                ) b
                ON a.userID = b.user_id AND
WHERE a.statusMsg LIKE '%search%' AND
      b.user_id IS NULL
LIMIT 5;

没有子查询的

或更好的方法：

SELECT a.*
FROM posts a
     LEFT JOIN myMembers b
         ON a.userID = b.id AND
            b.privacy = 1
     LEFT JOIN following c
         ON a.userID = c.user_id AND
            c.follower_id = 1
WHERE a.statusMsg LIKE '%search%' AND
      b.id IS NULL AND
      c.user_id IS NULL
LIMIT 5;

请参阅：A Visual Explanation of SQL Joins

Answer 3

尝试以下方法：

SET @my_user_id= 1;

SELECT * FROM posts p
INNER JOIN myMembers m ON p.user_id= m.id  
WHERE statusMsg LIKE '%'
AND privacy=0
AND user_id IN (SELECT follower_id FROM following f WHERE f.user_id=@my_user_id)
LIMIT 5

具有隐私条件检查的查询中的mysql查询

3 个答案: