Question

我需要在两列之后对MySQL表进行排序，但不像常规排序。在聊天应用程序中，我希望获得按时间戳字段排序的结果，但也按发件人

分组

CREATE TABLE messages (
  id int(10) unsigned NOT NULL AUTO_INCREMENT,
  timestamp timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP,
  sender int(10) unsigned NOT NULL,
  message char(255) NOT NULL,
  PRIMARY KEY (id)
) ENGINE=MyISAM AUTO_INCREMENT=9 DEFAULT CHARSET=utf8;

INSERT INTO messages VALUES ('1', '2011-02-28 01:58:24', '3', '1');
INSERT INTO messages VALUES ('2', '2011-02-28 01:58:28', '3', '2');
INSERT INTO messages VALUES ('3', '2011-02-28 01:58:35', '1', '5');
INSERT INTO messages VALUES ('4', '2011-02-28 01:58:36', '2', '7');
INSERT INTO messages VALUES ('5', '2011-02-28 01:58:38', '3', '3');
INSERT INTO messages VALUES ('6', '2011-02-28 01:58:39', '2', '8');
INSERT INTO messages VALUES ('7', '2011-02-28 01:58:40', '1', '6');
INSERT INTO messages VALUES ('8', '2011-02-28 01:58:41', '3', '4');

所以：

ORDER BY时间戳，发件人无用

ORDER BY发件人，时间戳非常好，但不会先显示旧邮件

SELECT timestamp, sender, message FROM messages ORDER BY sender IN (SELECT DISTINCT sender FROM messages ORDER BY timestamp), timestamp;

不起作用，因为我认为它必须工作。以下是我对此查询的期望（ofc不是我从此查询得到的结果：P）：

+---------------------+--------+---------+
| timestamp           | sender | message |
+---------------------+--------+---------+
| 2011-02-28 01:58:24 |      3 | 1       |
| 2011-02-28 01:58:28 |      3 | 2       |
| 2011-02-28 01:58:38 |      3 | 3       |
| 2011-02-28 01:58:41 |      3 | 4       |
| 2011-02-28 01:58:35 |      1 | 5       |
| 2011-02-28 01:58:40 |      1 | 6       |
| 2011-02-28 01:58:36 |      2 | 7       |
| 2011-02-28 01:58:39 |      2 | 8       |
+---------------------+--------+---------+

有什么想法吗？链接？提示？什么？在此先感谢，欢迎提出任何问题

Answer 1

它适用于你ORDER BY sender asc, timestamp desc吗？

<强>更新
你可能需要这样的东西：

SELECT a.timestamp, a.sender, a.message 
FROM messages a
INNER JOIN
 (SELECT b.sender_id, MIN(b.timestamp) as timestamp 
  FROM messages b GROUP BY sender
 )c ON (c.sender = a.sender)
ORDER BY c.timestamp, a.sender

Answer 2

SELECT * FROM messages ORDER BY sender, timestamp ASC;

将按发件人排序，然后按时间戳为您提供按时间戳排序的每个发件人数据。在MySQL中，当你使用多种排序时，它只能按一种排序，然后另一种排序。

你想要实现的是......好吧，不可能，你不能将发件人分组，如果他们不符合发送者的想法......我给的是你在MySQL中最接近的

SELECT ... ORDER BY字段IN（SELECT ...）不能处理重复字段

2 个答案: