MySQL 一对多子选择 max UNIX_TIMESTAMP() from date答案

【问题标题】：MySQL one to many subselect max UNIX_TIMESTAMP() from dateMySQL 一对多子选择 max UNIX_TIMESTAMP() from date
【发布时间】：2012-12-20 10:33:09
【问题描述】：

我有一个查询，除了从与帖子相关的 cmets 获取最大日期之外，它运行良好。

所以我想做的是：

关系：1 个帖子到许多 cmets
使用 max() 在 UNIX_TIMESTAMP() 中获取每个帖子的“最新评论日期”
按“最新发布日期”或“最新评论日期”对整个查询进行排序。因此，根据每行按“最新发布日期”或“最新评论日期”排序。
因此，顶部的记录要么是最新的帖子，要么是帖子的评论晚于任何会进入顶部的帖子。

任何帮助将不胜感激。

无需获取最大最新评论日期并按最新排序即可工作的查询

SELECT DISTINCT wallposts.p_id,wallposts.type,wallposts.value,wallposts.media,wallposts.youtube,wallposts.post_type,wallposts.tagedpersons,wallposts.title AS thetitle,wallposts.url,wallposts.description,wallposts.cur_image,wallposts.uip,wallposts.likes,wallposts.userid,wallposts.posted_by,wallposts.post as postdata,wallusers.*, UNIX_TIMESTAMP() - wallposts.date_created AS TimeSpent,wallposts.date_created,wallposts.course 
        FROM wallposts,wallusers
        where (
        wallposts.userid =4276 OR
        wallposts.tagedpersons LIKE '%4276%' OR
        EXISTS (SELECT * FROM wallcomments WHERE wallposts.p_id = wallcomments.post_id AND wallcomments.tagedpersons LIKE '%4276%')
        ) 
        AND wallusers.mem_id = wallposts.userid
        order by wallposts.p_id desc

我试图解决问题但失败的那个：

   SELECT DISTINCT wallposts.p_id,wallposts.type,wallposts.value,wallposts.media,wallposts.youtube,wallposts.post_type,wallposts.tagedpersons,wallposts.title AS thetitle,wallposts.url,wallposts.description,wallposts.cur_image,wallposts.uip,wallposts.likes,wallposts.userid,wallposts.posted_by,wallposts.post as postdata,wallusers.*, UNIX_TIMESTAMP() - wallposts.date_created AS TimeSpent,wallposts.date_created,wallposts.course 
                FROM wallposts,wallusers
                JOIN wallusers wu on wallposts.userid = wu.mem_id
                LEFT JOIN wallcomments wc ON wc.post_id(SELECT date_created as commentdate_created, UNIX_TIMESTAMP() - max(date_created) as latestcomment
                FROM wallcomments wc WHERE wallposts.p_id = wc.post_id LIMIT 1)
                where (
                wallposts.userid = 4276 OR
                wallposts.tagedpersons LIKE '%4276%' OR
                EXISTS (SELECT * FROM wallcomments WHERE wallposts.p_id = wallcomments.post_id AND wallcomments.tagedpersons LIKE '%4276%')
                ) 
                order by greatest(latestcomment, TimeSpent) DESC

【问题讨论】：

标签： mysql sql

【解决方案1】：

查询本身对我来说有点奇怪 - LEFT JOIN 似乎已损坏，请再次检查：

SELECT 
      DISTINCT wallposts.p_id,
      wallposts.type,
      wallposts.value,
      wallposts.media,
      wallposts.youtube,
      wallposts.post_type,
      wallposts.tagedpersons,
      wallposts.title AS thetitle,
      wallposts.url,
      wallposts.description,
      wallposts.cur_image,
      wallposts.uip,
      wallposts.likes,
      wallposts.userid,
      wallposts.posted_by,
      wallposts.post as postdata,
      wallusers.*,
      UNIX_TIMESTAMP() - wallposts.date_created AS TimeSpent,
      wallposts.date_created,
      wallposts.course 
FROM wallposts, wallusers
      JOIN wallusers wu 
            on wallposts.userid = wu.mem_id
      LEFT JOIN wallcomments wc 
            ON wc.post_id (
                  SELECT 
                        date_created as commentdate_created, 
                        UNIX_TIMESTAMP() - max(date_created) as latestcomment
                  FROM wallcomments wc 
                  WHERE wallposts.p_id = wc.post_id LIMIT 1
            )
WHERE (
            wallposts.userid = 4276 OR
            wallposts.tagedpersons LIKE '%4276%' OR
            EXISTS (
                  SELECT * 
                  FROM wallcomments 
                  WHERE wallposts.p_id = wallcomments.post_id 
                        AND wallcomments.tagedpersons LIKE '%4276%'
            )
      )
order by greatest(latestcomment, TimeSpent) DESC

【讨论】：

什么意思 LEFT JOIN 似乎已损坏。我不确定我是否需要使用 LEFT JOIN。我将您的代码复制并粘贴到 phpmyadmin 中，这是错误 - #1064 - 您的 SQL 语法有错误；检查与您的 MySQL 服务器版本相对应的手册，以在第 27 行的“SELECT date_created as commentdate_created,”附近使用正确的语法
我所做的一切 - 格式化给定的代码，使其可读
好的，并没有真正帮助我在写的时候已经读过了。为什么不直接编辑我的问题并重新格式化。