【发布时间】：2014-09-21 08:06:15
【问题描述】：
我有一个相当大的查询，它基本上向我的用户显示了我存储在数据库中的不同论坛：
$stmt = $dbh->prepare("
SELECT
c.forum_id as category_id,
c.forum_name as category_name,
t.forum_id as id,
t.forum_name as name,
t.forum_desc as description,
(SELECT COUNT(*) FROM forum_topics WHERE forum_id=t.forum_id AND topic_deleted=0) as topics_count,
(SELECT COUNT(*) FROM forum_posts WHERE forum_id=t.forum_id AND post_deleted=0) as posts_count,
(SELECT COUNT(*) FROM forum_posts WHERE topic_id=lp.topic_id AND post_deleted=0) as last_post_count,
lp.topic_id as last_post_topic_id,
lp.topic_title as last_post_topic_title,
lp.post_time as last_post_time,
lp.username as last_post_username
FROM forum_cats as t
JOIN forum_cats as c on c.forum_id = t.forum_type_id
left join (
SELECT
ft.topic_id,
ft.title as topic_title,
tmp.post_time,
u.username,
fp.forum_id
FROM
forum_posts fp
join forum_topics ft on ft.topic_id = fp.topic_id
join users u on u.id = fp.userid
join (
select forum_id, max(`post_time`) `post_time`
from forum_posts fp
where fp.post_deleted = 0
group by forum_id
) as tmp on (fp.forum_id = tmp.forum_id and fp.post_time = tmp.post_time)
where post_deleted = 0 and ft.topic_deleted = 0
) as lp on lp.forum_id = t.forum_id
where t.forum_active = 1 and c.forum_active = 1
order by category_id, t.forum_id
");
$stmt->execute();
然后我做一个while循环来显示所有记录：
while (($row = $stmt->fetch())) {
echo $row['name'];
}
问题是，在 while 循环期间，我得到了很好的结果有时！
应该是这样的：
forum1
forum2
forum3
forum4
forum5
forum6
等等
但有时我会得到这样的结果：
forum1
forum1
forum1
forum1
forum2
forum3
forum4
forum5
forum6
某些行（哪一行是非常随机的）正在“复制”。
有人可以帮我解释一下吗？
【问题讨论】：
-
想必查询
SELECT t.forum_id FROM forum_topics t会产生同样的错误？ -
@Strawberry 你愿意详细说明吗？
-
只是一个疯狂的猜测，但是......我会说你的第三个加入（子查询）在主查询上带来了帖子，因为你可能在一个论坛上有很多帖子。你能单独运行子查询（你把它命名为
lp）并检查是否有重复的forum_id字段？ -
只是试图确定问题出在 PHP 还是 MySQL 上
-
这个连接看起来很奇怪：
FROM forum_cats as t JOIN forum_cats as c on c.forum_id = t.forum_type_id。什么是forum_cats（类别？），为什么需要通过 forum_id 和 type_id 加入该表本身？它看起来像一个错误，即使不是，它也可能返回重复项。
标签： php mysql sql pdo inner-join