Question

当我有两张表时，如何显示最近的帖子，这两张表都包含一个名为 creation_date 的列

如果我所要做的就是根据创建的帖子获取最新的帖子，这将很简单，但如果帖子包含回复，我需要将其纳入等式。如果帖子有更新的回复，我想获得created_on值的回复，但也获得帖子post_id和subject。

帖子表格结构：

CREATE TABLE `posts` (
  `post_id` bigint(20) unsigned NOT NULL auto_increment,
  `cat_id` bigint(20) NOT NULL,
  `user_id` bigint(20) NOT NULL,
  `subject` tinytext NOT NULL,
  `comments` text NOT NULL,
  `created_on` datetime NOT NULL,
  `status` varchar(10) NOT NULL default 'INACTIVE',
  `private_post` varchar(10) NOT NULL default 'PUBLIC',
  `db_location` varchar(10) NOT NULL,
  PRIMARY KEY  (`post_id`)
) ENGINE=MyISAM  DEFAULT CHARSET=latin1 AUTO_INCREMENT=7 ;

回复表格结构：

CREATE TABLE `replies` (
  `reply_id` bigint(20) unsigned NOT NULL auto_increment,
  `post_id` bigint(20) NOT NULL,
  `user_id` bigint(20) NOT NULL,
  `comments` text NOT NULL,
  `created_on` datetime NOT NULL,
  `notify` varchar(5) NOT NULL default 'YES',
  `status` varchar(10) NOT NULL default 'INACTIVE',
  `db_location` varchar(10) NOT NULL,
  PRIMARY KEY  (`reply_id`)
) ENGINE=MyISAM  DEFAULT CHARSET=latin1 AUTO_INCREMENT=5 ;

到目前为止，这是我的查询。我删除了提取日期的尝试。

$strQuery = "SELECT posts.post_id, posts.created_on, replies.created_on, posts.subject ";
$strQuery = $strQuery."FROM posts ,replies ";
$strQuery = $strQuery."WHERE posts.post_id = replies.post_id ";
$strQuery = $strQuery."AND posts.cat_id = '".$row->cat_id."'";

Answer 1

$strQuery = "
  SELECT posts.post_id, GREATEST(posts.created_on, replies.created_on)  AS latestDate, posts.subject
  FROM posts, replies
  WHERE posts.post_id = replies.post_id
  AND posts.cat_id = {$row->cat_id}
  GROUP BY posts.post_id
  ORDER BY latestDate DESC;
";

更新：在第二次看，上面实际上是不正确的，因为它不包括那些还没有任何回复的帖子。更正确的方法是：

$strQuery = "
  SELECT posts.post_id, GREATEST(posts.created_on, replies.created_on) AS latestDate,
  FROM posts
  LEFT JOIN replies ON (posts.post_id = replies.post_id)
  WHERE posts.cat_id = {$row->cat_id}
  GROUP BY posts.post_id
  ORDER BY latestDate DESC
  LIMIT 0,1;
";

Answer 2

SELECT posts.post_id，posts.subject，replies.post_id

来自帖子   LEFT JOIN回复ON post.post_id = replies.post_id

WHERE posts.cat_id ='$ row-＆gt; cat_id'

ORDER BY posts.post_id DESC，replies.post_id DESC

没有回复的那个将返回NULL，您可以在输出中使用PHP过滤掉。

Answer 3

获取最新帖子，对帖子的最新回复，然后获取最新的帖子。

这使用order by created_on desc limit 1仅从表中获取最后一项。我建议在两个表的created_on列上添加密钥，在回复表中为post_id列添加密钥。

更新：cat_id也需要建立索引。

select * from (
select * from 
(
select p.post_id, p.created_on , 'post' as post_type
from posts p
where p.cat_id = '$row->cat_id'
order by p.created_on  desc limit 1
)post
union 
select * from 
(
select p.post_id, r.created_on , 'reply'
from posts p
inner join replies r on r.post_id = p.post_id
where p.cat_id = '$row->cat_id'
order by r.created_on  desc limit 1
)reply
)big order by big.created_on limit 1;

根据日期获取最新帖子

3 个答案: