Mysql 根据第一条消息获取最新未读消息

从存储用户之间消息的表中检索数据是一个问题。 这是表格：

CREATE TABLE messages
(
    id INT UNSIGNED NOT NULL AUTO_INCREMENT,
    sender  VARCHAR(20), 
    recipient  VARCHAR(30),
    content TEXT,
    is_read TINYINT(1),
    created_at DATETIME,
    PRIMARY KEY (`id`) ,
    INDEX idx_sender (sender) ,
    INDEX idx_recipient (recipient)
);

INSERT INTO messages (id, sender, recipient, content, is_read, created_at)
VALUES
-- Alice and George
(1, 'Alice', 'George', 'Happy new year', 1, '2012-12-24 23:05:00'),
(2, 'George', 'Alice', 'It is chrimas night...', 1, '2012-12-24 23:10:00'),
(3, 'Alice', 'George', 'Happy Xmas then', 0, '2012-12-25 00:00:00'),
-- John and Paul
(4, 'John', 'Paul', 'Hi Paul', 1, '2012-12-26 09:00:00'),
(5, 'Paul', 'John', 'Hi John', 1, '2012-12-26 09:05:00'),
(6, 'John', 'Paul', 'Have you done this ?', 1, '2012-12-26 09:10:00'),
(7, 'Paul', 'John', 'No I was unpacking my gifts', 0, '2012-12-26 09:05:00'),
-- George and Tim
(8, 'George', 'Tim', 'How was the end of the world ?', 1, '2012-12-22 10:10:00'),
(9, 'Tim', 'George', 'Really nice !', 0, '2012-12-22 10:15:00'),
-- John and Tim
(10, 'John', 'Tim', 'I don\'t know if I should fire you for new year\'s eve', 1, '2012-12-27 15:20:00'),
(11, 'Tim', 'John', 'That is a great idea!', 0, '2012-12-27 15:20:00');

假设乔治和约翰是经理，其他人是雇员。 我需要检索经理是收件人的最新未读邮件。 同时，我必须只检索那些同时也是对话发起人的消息

因此，结果必须是：

• 消息id 7:'保罗'，'约翰'，'不，我正在打开我的礼物'，01212-2609:05:00
• 消息id 9:'蒂姆'，'乔治'，'真不错'，01212-22 10:15:00
• 信息id 11:‘蒂姆’、‘约翰’、‘这是个好主意！’，2012年12月27日15:20:00

我做了一个查询，几乎是这样，但是缺少消息id 11的行：

SELECT
    m.*
FROM
    messages m
INNER JOIN (
    -- retrieve the first message (fm)
    SELECT t.sender, t.recipient
    FROM (
        SELECT id, sender, recipient, content, created_at,
        IF ( sender IN ('John', 'George'), sender, recipient ) AS the_other
        FROM messages
        WHERE
            sender  IN ('John', 'George')
            OR recipient IN ('John', 'George')
        ORDER BY
        created_at ASC
    ) t
    GROUP BY
        the_other
    HAVING t.sender IN ('John', 'George')
) fm ON fm.recipient = m.sender
    AND fm.sender = m.recipient
WHERE
    m.recipient IN ('John', 'George')
    AND m.is_read = 0
ORDER BY
    m.created_at DESC
LIMIT 0, 10

缺少消息id 11，因为子查询正在由\u other进行分组。 如果我按发件人和收件人拆分“分组依据”，它将检索邮件id 3，但这是不需要的行

---

解决我的问题的SQL应该是什么？

可以使用下面的查询：

select a.* from
(select id, sender, recipient, content, is_read, max(created_at)
from message where recipent in ('John', 'George') and is_read = 0 
group by sender) a,    message b (select id, sender, recipient,
content, is_read, min(created_at) 
from message where sender in ('John', 'George') group by recipient) b
where a.sender=b.recepient

---

最后我找到了一个解决方案，但我认为这不是最优化的查询：

SELECT
    m.*
FROM
    messages m
INNER JOIN (
    -- retrieve the first messages (fm)

    SELECT t.sender, t.recipient
    FROM (
        SELECT id, sender, recipient, content, created_at,
        IF ( sender = 'John', recipient, sender ) AS the_other
        FROM messages
        WHERE
            sender  = 'John'
            OR recipient = 'John'
        ORDER BY
        created_at ASC
    ) t
    GROUP BY
        the_other
    HAVING t.sender = 'John'

    UNION

    SELECT t.sender, t.recipient
    FROM (
        SELECT id, sender, recipient, content, created_at,
        IF ( sender = 'George', recipient, sender ) AS the_other
        FROM messages
        WHERE
            sender  = 'George'
            OR recipient = 'George'
        ORDER BY
        created_at ASC
    ) t
    GROUP BY
        the_other
    HAVING t.sender = 'George'

) fm ON fm.recipient = m.sender
    AND fm.sender = m.recipient
WHERE
    m.recipient IN ('John', 'George')
    AND m.is_read = 0
ORDER BY
    m.created_at DESC
LIMIT 0, 10

---

你所说的“发起”是什么意思？为什么不包括记录ID:

3

？在initiated中，我的意思是对话的第一条消息是由经理John或George发送的。记录3不能包括在内，因为在此对话中，第一条消息是由Alice而不是George发送的。在我的例子中有4个对话，爱丽丝和乔治，约翰和保罗，乔治和蒂姆，约翰和蒂姆。最后3次对话是经理发起的唯一对话。我确认了您的查询错误，但它给了我错误的结果：我不想要记录3，记录11缺失