php - MySQL : Order by and Group By combining not giving the latest record

Question

使用以下查询，我正在寻找一种解决方案来获取具有某些条件的最新记录。但它给了我第一条记录，而不是最新的。我认为它只考虑小组请多多指教

SELECT * FROM `contacts` WHERE `id_receiver`=1  GROUP BY `id_thread` ORDER BY created DESC

id   id_sender   id_thread sender_email   id_receiver      created(datetime)
1    2             2         51             1                2012-03-24 13:44:48
2    4             4         1              5                 2012-04-26 13:46:05
3    2             2         51             1                2012-04-09 12:12:30

要求的输出

id   id_sender  id_thread sender_email   id_receiver      created(datetime)
3    2           2         51             1                2012-04-09 12:12:30

我做了一个测试，只是交换 order by 和 group by ，给我一个错误。

任何人都可以看看这个吗？谢谢。

EDIT 编辑问题，忘了写id_thread

Answer 1

当表中没有 id_thread 列时，如何GROUP BY id_thread？

SELECT * 
FROM contacts 
WHERE id_receiver = 1 
                                 --- GROUP BY id_thread
                                 --- removed 
ORDER BY created DESC
LIMIT 1                          --- only show one row

---

根据您的评论，您想要的是每个 id_thread 的最新(按 created 排序)行，这是一个不同且更复杂的查询。这种查询甚至有一个标签，名为 [greatest-n-per-group] .

SELECT c.* 
FROM contacts AS c
  JOIN
    ( SELECT id_thread, MAX(created) AS created 
      FROM contacts 
      WHERE id_receiver = 1  
      GROUP BY id_thread
    ) AS g 
    ON (g.id_thread, g.created) = (c.id_thread, c.created) 
WHERE c.id_receiver = 1