2

我在从存储用户之间消息的表中检索数据时遇到问题。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 George 和 John 是经理，其他人是员工。我需要检索管理员是收件人的最新未读消息。同时，我必须只检索它们也是对话发起者的那些消息。

所以结果必须是：

  • message id 7 : 'Paul', 'John', 'No I was unpacking my gift', 0, 2012-12-26 09:05:00
  • 消息 id 9 : 'Tim', 'George', 'Really nice', 0, 2012-12-22 10:15:00
  • message id 11 : 'Tim', 'John', 'That is a great idea!', 0, 2012-12-27 15:20:00

我进行了一个查询，几乎就是这样，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，因为子查询按 the_other 分组。如果我按发件人和收件人拆分“分组依据”，它将检索消息 id 3，但它是不需要的行。

解决我的问题的 SQL 应该是什么？

4

2 回答 2

0

Finally I've found a solution but I don't think this is the most optimized query :

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

http://sqlfiddle.com/#!2/30f5a/17/0

于 2012-12-27T07:48:19.213 回答
0

可以使用以下查询：

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
于 2012-12-26T09:57:38.953 回答