Question

我想要表记录如下：

---------------------------------------------------------------------------
id | receiver_user_id | sender_user_id | message_text | insertdate
---------------------------------------------------------------------------
6  | 33               | 42             | OLD          | 2013-05-08 10:08:53
8  | 33               | 43             | ddddd        | 2013-05-07 19:01:45
7  | 33               | 38             | Ipsum        | 2013-04-25 10:27:35
---------------------------------------------------------------------------

我正在使用此查询：

SELECT *
FROM (`player_messages`)
WHERE `receiver_user_id` =  '33'
GROUP BY sender_user_id
ORDER BY `player_messages`.`insertdate` DESC

获取如下表格记录。

---------------------------------------------------------------------------
id | receiver_user_id | sender_user_id | message_text | insertdate
---------------------------------------------------------------------------
6  | 33               | 43             | ddddd        | 2013-05-07 19:01:45
4  | 33               | 42             | NEW          | 2013-05-07 10:08:58
7  | 33               | 38             | Ipsum        | 2013-04-25 10:27:35
---------------------------------------------------------------------------

请帮忙。提前谢谢。

Answer 1

您正在选择表SELECT *中的所有字段，但您只按sender_user_id进行分组，非聚合列的值将不受管理，也不受订单的影响。

您应该像这样编写查询：

SELECT   player_messages.*
FROM     player_messages
WHERE    (receiver_user_id, sender_user_id, insertdate) IN (
           SELECT   receiver_user_id, sender_user_id, MAX(insertdate)
           FROM     player_messages
           WHERE    receiver_user_id='33'
           GROUP BY receiver_user_id, sender_user_id)
ORDER BY player_messages.insertdate DESC

这将返回所有具有每个接收者和发送者组合的最大插入日期的player_messages行。

Answer 2

当您查询MySQL数据库时，只需在查询结尾添加“ORDER BY”，即可按升序或降序对任何字段进行排序。您可以使用 ORDER BY field_name ASC 进行升序排序，或使用 ORDER BY field_name DESC 进行降序排序。

例如

"SELECT * FROM address ORDER BY name ASC"

如何在mysql中使用group by以降序获取数据

2 个答案: