我有一個問題從用戶之間存儲消息的表中檢索數據。 下面是表:根據第一條消息獲取最新的未讀消息
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');
假設喬治和約翰是經理人,和其他人是僱員。 我需要檢索管理員是收件人的最新未讀郵件。 同時,我必須只檢索那些他們也是對話發起人的消息。
那麼結果一定是:
- 消息ID 7: '保羅', '約翰', '不,我是拆包我的禮物',0,2012-12-26 9點05分00秒
- message id 9:'Tim','George','真的很好',0,2012-12-22 10:15:00
- message id 11:'Tim','John','That is a ',0,2012-12-27 15:20:00
我做了一個查詢,它幾乎是,但消息id 11的行缺少:
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
由於子查詢由the_other分組,因此缺少消息ID 11。 如果我按發件人和收件人分組「發件人」,它將檢索郵件標識3,但它是不需要的行。
什麼是應該解決我的問題的SQL?
做什麼你的意思是發起?爲什麼不包括記錄ID:'3'? –
在啓動時,我的意思是一個對話的第一條消息是由經理髮送的,所以John或George。 記錄3不能包含,因爲在這個對話中,第一條消息是由Alice發送的,而不是由George發送的。 在我的例子中,有4個對話,愛麗絲和喬治,約翰和保羅,喬治和蒂姆,約翰和蒂姆。最後3次對話是唯一由經理髮起的對話。 – Shaolin