少于运算符给出奇怪的结果

Question

所以我有这个查询将几个表连接在一起并返回数据

SELECT * FROM userposts up
INNER JOIN userpostmeta upm
ON up.up_postID = upm.upm_postID
INNER JOIN userbasicprofile ubp
ON up.up_userID = ubp.ubp_userID
WHERE up.up_userID = :self OR up.up_userID IN (SELECT ufs_userID2 FROM userfriends where ufs_userID1 = :u)
AND
up.up_indexid < $startIndex AND up.up_indexid > 0
ORDER BY up.up_indexid DESC
LIMIT $limit

表格userposts有一个名为'up_indexid'的列，它是AUTO INCREMENT

问题是 ，当我为支持31发送$startIndex的值时，它显示indexid 31以下的indexid ，但也显示其上方的帖子。

为什么会这样呢？ 我已经尝试了多个断点，但是似乎没有任何解决方案。

Answer 1

原因与<无关，这是由于您的mysql查询中包含OR

SELECT * FROM userposts up
INNER JOIN userpostmeta upm
ON up.up_postID = upm.upm_postID
INNER JOIN userbasicprofile ubp
ON up.up_userID = ubp.ubp_userID
WHERE up.up_userID = :self 
OR up.up_userID #OR makes things unexpected
  IN (SELECT ufs_userID2 FROM userfriends where ufs_userID1 = :u) 
AND
up.up_indexid < $startIndex AND up.up_indexid > 0
ORDER BY up.up_indexid DESC
LIMIT $limit

Answer 2

尝试这样做：

'SELECT * FROM userposts up
INNER JOIN userpostmeta upm
ON up.up_postID = upm.upm_postID
INNER JOIN userbasicprofile ubp
ON up.up_userID = ubp.ubp_userID
WHERE up.up_userID = :self OR up.up_userID IN (SELECT ufs_userID2 FROM userfriends where ufs_userID1 = :u)
AND
up.up_indexid < ' . intval($startIndex) . ' AND up.up_indexid > 0
ORDER BY up.up_indexid DESC
LIMIT ' . intval($limit)

我注意到您正在使用Binding和字符串中的变量，为什么不只绑定startIndex并限制呢？ 另外，您可能想看一下偏移量，这可能是一个更好的解决方案，例如LIMIT 100，10（所以从第10个条目开始有100个条目）

Answer 3

根据https://dev.mysql.com/doc/refman/8.0/en/operator-precedence.html OR的优先级低于AND，因此您的WHERE子句解释为：

WHERE up.up_userID = :self OR (up.up_userID IN (SELECT ufs_userID2 FROM userfriends where ufs_userID1 = :u)
AND
up.up_indexid < $startIndex AND up.up_indexid > 0)
ORDER BY up.up_indexid DESC
LIMIT $limit

我想您想要的是以下内容：

WHERE (up.up_userID = :self OR up.up_userID IN (SELECT ufs_userID2 FROM userfriends where ufs_userID1 = :u))
AND
up.up_indexid < $startIndex AND up.up_indexid > 0
ORDER BY up.up_indexid DESC
LIMIT $limit