Question

在MySql中我有表：

idPost | idPostParent | postText                              | dateCreated         |
1      | 1            |  This is parent post no1              | 2012-01-01 12:00:00 |
2      | 2            |  This is parent post no2              | 2012-01-02 13:00:00 |
3      | 1            |  This is first reply on idPost:1      | 2012-01-02 13:30:00 | 
4      | 4            |  This is parent post no3              | 2012-01-04 10:00:00 |
5      | 2            |  This is first reply on idPost:2      | 2012-01-04 11:00:00 |
6      | 1            |  This is second reply on idPost:1     | 2012-01-05 15:00:00 |
7      | 2            |  This is second reply on idPost:2     | 2012-01-06 17:00:00 |

注意：

如果idPost = idPostParent
REPLY post is detedted idPostParent和回复是与idPostParent中的post writen相关。

我需要SQL查询来按照某些规则对表中的记录集进行排序和分组：

帖子必须按idPostParent分组（父帖先是然后是它回复）
最新输入的PARENT帖子或最新输入的回复必须位于顶部。

结果集应为：

idPost | idPostParent | postText                              | dateCreated         |
2      | 2            |  This is parent post no2              | 2012-01-02 13:00:00 |
5      | 2            |  This is first reply on idPost:2      | 2012-01-04 11:00:00 |
7      | 2            |  This is second reply on idPost:2     | 2012-01-06 17:00:00 |
1      | 1            |  This is parent post no1              | 2012-01-01 12:00:00 |
3      | 1            |  This is first reply on idPost:1      | 2012-01-02 13:30:00 |
6      | 1            |  This is second reply on idPost:1     | 2012-01-05 15:00:00 |
4      | 4            |  This is parent post no3              | 2012-01-04 10:00:00 |

原因： PARENT post idPost = 2有最新输入的回复帖子，因此其主题必须位于表格顶部。

感谢任何可能为解决方案做出贡献的人！

Answer 1

这适用于您的测试数据

SELECT
posts.*
FROM posts
INNER JOIN 
  (
    SELECT idPostParent, MAX(dateCreated) as dateLastAnswer
    FROM posts
    GROUP by idPostParent
  ) AS pp ON posts.idPostParent=pp.idPostParent
ORDER BY pp.dateLastAnswer DESC, idPost ASC

Answer 2

这是一种方式：

SELECT p.*
FROM posts p
LEFT JOIN
 (SELECT idPostParent, MAX(dateCreated) AS time_of_newest
  FROM posts
  GROUP BY idPostParent) p2
 ON p.idPostParent = p2.idPostParent
ORDER BY time_of_newest DESC, idPost=p.idPostParent DESC, dateCreated DESC

说明：

子查询

SELECT idPostParent, MAX(dateCreated) AS time_of_newest
  FROM posts
  GROUP BY idPostParent

选择每个“线程”（idPostParent）创建的最大日期。

这是主LEFT JOIN表的posts d，因此每个线程都有一个time_of_newest用于该线程。

我们按time_of_newest DESCENDING排序（这会将线程2放在线程4前面的线程1前面。）

然后，我们按idPost=idPostParent1 DESC排序，以便在回复之前获得父帖（父帖在这里有1个，回复所有都有0，因为我们排序降序父帖首先出现。）

最后，我们按dateCreated DESC排序，以便按顺序获得回复。

Answer 3

这样的东西？

SELECT op.*, (SELECT MAX(ip.dateCreated) FROM posts ip WHERE ip.idPostParent = op.idPostParent) newestParentReply 
FROM posts op ORDER BY newestParentReply DESC, op.dateCreated ASC

尚未测试过。使用必须为每个帖子执行的子查询，它的表现也非常糟糕。

MySql：需要SQL查询来按一些规则对表中的记录集进行排序和分组

3 个答案: