我正在开发一个消息传递系统，并试图以正确的方式获取数据，但是却被卡住了。
#Message Table
CREATE TABLE `message` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`subject` varchar(255) NOT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=7 DEFAULT CHARSET=latin1;
INSERT INTO `message` (`id`, `subject`)
VALUES
(1, 'Test'),
(2, 'Test Again'),
(6, 'Nice!'),
(7, 'Next');
#Message User Table
CREATE TABLE `message_user` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`message_id` int(11) NOT NULL,
`user_id` int(11) NOT NULL,
`interlocutor` int(11) DEFAULT NULL,
`body` text,
`folder` enum('inbox','sent') NOT NULL,
`starmark` tinyint(1) NOT NULL DEFAULT '0',
`unread` tinyint(1) NOT NULL DEFAULT '1',
`deleted` enum('none','trash','deleted') NOT NULL DEFAULT 'none',
`created_date` datetime DEFAULT CURRENT_TIMESTAMP,
PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=28 DEFAULT CHARSET=latin1;
INSERT INTO `message_user` (`id`, `message_id`, `user_id`, `interlocutor`, `body`, `folder`, `starmark`, `unread`, `deleted`, `created_date`)
VALUES
(1, 1, 1, 2, 'Hi, how are you?', 'sent', 0, 1, 'none', '2018-10-23 09:36:02'),
(2, 1, 2, 1, 'Hi, how are you?', 'inbox', 0, 1, 'none', '2018-10-23 09:36:02'),
(3, 1, 2, 1, 'I am good thanks, you?', 'sent', 0, 1, 'none', '2018-10-23 09:46:02'),
(4, 1, 1, 2, 'I am good thanks, you?', 'inbox', 0, 1, 'none', '2018-10-23 09:46:02'),
(13, 6, 1, 2, 'Hi how are you', 'sent', 0, 0, 'none', '2018-10-23 15:40:43'),
(14, 6, 2, 1, 'Hi how are you', 'inbox', 0, 1, 'none', '2018-10-23 15:40:43'),
(16, 6, 1, 2, 'Also, what time is it at yours?', 'sent', 0, 0, 'none', '2018-10-23 15:44:20'),
(17, 6, 2, 1, 'Also, what time is it at yours?', 'inbox', 0, 1, 'none', '2018-10-23 15:44:20'),
(18, 6, 2, 1, 'Hey and 18:44', 'sent', 0, 0, 'none', '2018-10-23 15:44:54'),
(19, 6, 1, 2, 'Hey and 18:44', 'inbox', 0, 1, 'none', '2018-10-23 15:44:56'),
(20, 6, 2, 1, 'You ok?', 'sent', 0, 0, 'none', '2018-10-23 15:44:56'),
(21, 6, 1, 2, 'You ok?', 'inbox', 0, 1, 'none', '2018-10-23 15:44:54'),
(22, 2, 2, 1, 'Hey', 'inbox', 0, 1, 'none', '2018-10-23 19:20:23'),
(23, 2, 1, 2, 'Hey', 'sent', 0, 1, 'none', '2018-10-23 19:20:23'),
(24, 7, 2, 1, 'Hello', 'sent', 0, 1, 'none', '2018-10-23 19:29:36'),
(25, 7, 1, 2, 'Hello', 'inbox', 0, 1, 'none', '2018-10-23 19:29:55'),
(26, 7, 1, 2, 'Hey!', 'sent', 0, 1, 'none', '2018-10-23 19:30:30'),
(27, 7, 2, 1, 'Hey!', 'inbox', 0, 1, 'none', '2018-10-23 19:30:43');
我正在尝试获取有关用户收件箱（ID 1）的消息。我想在未删除的地方显示收到的最新消息。除此之外，我还要有一个标志，指示我是否已回复该邮件。
上面的数据显示有4条消息。
消息1显示了用户1发送消息并获得响应的示例。身体应该显示“我很好，谢谢？”来自ID4。应为0。
消息2不应该显示，因为我给他们发送了一条消息，他们还没有回复。
消息6显示了混合对话的示例。他们对我的最后一次回应两次。身体应该显示“你还好吗？”来自ID 21。
消息7显示了我已答复的消息示例。正文应显示ID 25中的“ Hello”。由于ID 26而应显示为1。
我的尝试
SELECT dt.*
FROM (
SELECT m.id,
m.subject,
mu.id AS message_user_id,
mu.message_id,
mu.user_id,
mu.interlocutor,
mu.body,
mu.folder,
mu.starmark,
mu.unread,
mu.deleted,
mu.created_date,
Row_number()
OVER (PARTITION BY m.id
ORDER BY field(mu.folder, 'sent', 'inbox') DESC) AS row_no
FROM message m
JOIN message_user mu
ON m.id = mu.message_id
WHERE mu.deleted = 'none'
AND mu.user_id = 1
AND folder = 'inbox') AS dt
WHERE dt.row_no = 1
ORDER BY dt.id DESC;
此处未发出标记，并且消息ID 6显示响应ID 19而不是ID 21，因为它们两次答复。