Question

好的，所以在试图解决10个青少年的问题后，我不太清楚如何解决它。

我有1个MySQL查询从数据库中提取所有10个最新帖子，并在帖子表中显示在博客页面的第0页上。我使用LIMIT和偏移量，这样PHP每页只能显示10个帖子。这很有用：

$sql = "
SELECT u.name
     , u.avatar
     , p.id
     , p.user_id
     , p.title
     , p.article
     , DATE_FORMAT(p.set_in,'%d/%m/%Y') date
     , DATE_FORMAT(p.last_edited,'%d/%m/%Y->%H:%i') edited
     , p.genre
     , p.band_image
     , p.albums 
  FROM posts p 
  JOIN users u 
    ON u.id = p.user_id 
 ORDER 
    BY p.set_in DESC
 LIMIT $offset, $rec_limit
";

现在我希望MySQL只选择属于我提供的帖子的评论，而不是将所有评论和使用PHP匹配的帖子与帖子的相关ID相匹配，但我似乎无法破解由于某种原因它失败了。基于可以删除帖子的事实，我不能使用ID范围的一些静态逻辑。

现在这是我的查询，但这是一个非常糟糕的问题，并不适用于更大的网站：

$sql3 = "SELECT u.name,u.avatar,p.id,p.user_id,DATE_FORMAT(c.post_date,'%d/%m/%Y->%H:%i') date, c.ctitle, c.comment, c.id, c.user_id, c.post_id cid FROM comments c "
            . " JOIN users u ON u.id = c.user_id "
            . " JOIN posts p ON c.post_id = p.id "
            . " ORDER BY c.post_date DESC";

这是评论表：

id  post_id user_id ctitle  comment post_date   
1   40  1   hinew   hinew   2017-08-08 00:41:10 
3   40  1   Another Comment test comment    2017-08-08 00:49:15 
4   45  20  How are you fine    2017-08-08 01:06:30 
5   1   1   aftersomefix    yeahhhh 2017-08-08 01:14:12 
6   1   26  dsfgdfg dfgdfg  2017-08-08 01:14:58 
7   45  1   TEST    TEST    2017-08-08 20:42:38

这是帖子表：

id  user_id title   article set_in      last_edited genre   band_image  albums  
1   1   Demo Text   This is the first post demo text    2017-08-05 18:40:55 2017-08-07 21:17:04 yoyo    2017.08.07.20.17.04-02aacec988bf439c277e2a2b611a23...   popo    
18  19  This is a test  test    2017-08-06 18:43:57 2017-08-07 21:18:11 another test    2017.08.07.20.18.11-177120fbd1a8951e2a70907f5600e5...   wow this is a test  
19  20  This is a 3ed   TEST    2017-08-06 18:49:10 2017-08-07 21:19:14 So many test moses  2017.08.07.20.19.14-17362774_10154643389487979_824...   yes i know we have many tests   
38  1   rtyrtyrty   asdasd  2017-08-07 15:19:57 2017-08-07 21:14:56 Metalcore   2017.08.07.20.14.56-17098309_963035173797767_82275...   aert
jhkghjk
aertaert    
39  1   Dude    Yes I think it does!    2017-08-07 19:54:21 2017-08-07 21:11:47 Is this actually working?   2017.08.07.19.00.53-81c0e26d68e0d29ceb619758e164da...   hi  
40  1   Test albums This is a decp  2017-08-07 20:16:26 2017-08-07 21:11:23 albums genre    2017.08.07.20.01.50-tenor.gif   one,two,tree,four,five,789789,lol   
41  1   BAND EX 1   DESC EX 1   2017-08-08 00:27:45 0000-00-00 00:00:00 GENRE EX 1  2017.08.07.23.27.45-19399240_10158895409495261_149...   EX 1    
42  1   Band ex2    Desc ex 2   2017-08-08 00:28:19 0000-00-00 00:00:00 Genre ex2   2017.08.07.23.28.19-13240136_1004564029622092_8185...   ex 2    
43  1   Name 3  Desc 3  2017-08-08 00:28:52 0000-00-00 00:00:00 Genre 3 2017.08.07.23.28.52-reptilian-death-the-dawn-of-co...   3   
44  1   Name 4  4   2017-08-08 00:29:15 0000-00-00 00:00:00 4   2017.08.07.23.29.15-Best Melodic Death Metal Cover...   4   
45  1   WHAT    hehe    2017-08-08 00:31:52 0000-00-00 00:00:00 MURDER  2017.08.07.23.31.52-Best Melodic Death Metal Cover...   cool

我试图制作一个对我不起作用的WHERE IN，并且作为SQL noobie我找不到包含分页因素的任何相关解决方案。

Answer 1

从第一个查询中删除p.id以外的所有内容，并将其用作子查询。然后将其与评论表一起加入：

SELECT c.*, u.* -- select the columns you need
FROM comments c
JOIN users u ON u.id = c.user_id
JOIN (
    SELECT p.id -- other columns if needed in the outer query
    FROM posts p 
    ORDER BY p.set_in DESC
    LIMIT $offset, $rec_limit
) p ON p.id = c.post_id

MySQL仅选择属于在特定页面上查看的帖子的评论（使用LIMIT进行分页）

1 个答案: