Question

表格结构

    CREATE TABLE IF NOT EXISTS `mail_box` (
      `msg_id` int(11) NOT NULL AUTO_INCREMENT,
      `sender_id` int(11) NOT NULL,
      `receiver_id` int(11) NOT NULL,
      `message` text NOT NULL,
      `date` timestamp NOT NULL,
      `attachment` varchar(255) NOT NULL,
      `status` tinyint(1) NOT NULL,
      PRIMARY KEY (`msg_id`)
    ) ENGINE=InnoDB  DEFAULT CHARSET=latin1 AUTO_INCREMENT=10 ;

    CREATE TABLE IF NOT EXISTS `users` (
    `id` int(11) NOT NULL,
    `name` varchar(255) NOT NULL
     ) ENGINE=InnoDB DEFAULT CHARSET=latin1;

需要查询列出每个用户的最新5条消息。

查询我尝试使用信息中心列表

SELECT usr.name as Receiver,usr1.name as Sender, message,date
FROM mail_box 
JOIN users as usr on usr.id = receiver_id 
JOIN users as usr1 on usr1.id = sender_id 
ORDER BY date DESC
LIMIT 5

此查询将我的结果限制为5，不显示每个用户的最新5条消息。

Answer 1

标准SQL有窗口函数，很容易解决这个问题，但mysql还不支持窗口函数。在auto_increment中使用myisam表的特殊功能应该可以解决问题：

DROP TEMPORARY TABLE IF EXISTS _tmp_user;
CREATE TEMPORARY TABLE IF NOT EXISTS _tmp_user(sender_id int not null, send_order int not null auto_increment, msg_id int not null, primary key (sender_id,send_order), unique key (msg_id)) ENGINE=MYISAM;

INSERT _tmp_user(sender_id,send_order,msg_id)
SELECT m.sender_id,NULL,m.msg_id
FROM mail_box m
ORDER BY `date`
DESC;

SELECT usr.name as Receiver,usr1.name as Sender, message,date
FROM _tmp_user t
INNER JOIN mail_box m
ON t.msg_id=m.msg_id
JOIN users as usr on usr.id = m.receiver_id 
JOIN users as usr1 on usr1.id = m.sender_id 
WHERE t.send_order<=5;

Mysql消息应用程序列表来自每个用户的最新5条消息

查询我尝试使用信息中心列表

1 个答案: