加入3個表格和（限制2行ORDER BY time DESC）

Question

我知道這個問題已經被問了很多次了，但是我在執行時遇到了問題。
我做了一個減少的例子，所以很容易重現。
我想加入3個表，但在最後一個我想限制在2行DESC

CREATE TABLE `cars` (
`car_id` int(11) NOT NULL AUTO_INCREMENT, 
`plate` varchar(10) NOT NULL, 
`km` int(11) NOT NULL, 
`status` tinyint(1) NOT NULL, 
PRIMARY KEY (`car_id`) 
) ENGINE=MyISAM DEFAULT CHARSET=latin1 AUTO_INCREMENT=6 ; 
INSERT INTO `cars` (`car_id`, `plate`, `km`, `status`) VALUES 
(1, 'ABC1234', 130123, 1), 
(2, 'DEF1234', 100123, 1), 
(3, 'QWE1234', 5000, 1), 
(4, 'ASD1234', 3000, 1), 
(5, 'ZXC1234', 23000, 0); 

---

CREATE TABLE `cars_to_users` (
`car_id` int(11) NOT NULL, 
`user_id` int(11) NOT NULL, 
UNIQUE KEY `car_id` (`car_id`,`user_id`) 
) ENGINE=MyISAM DEFAULT CHARSET=latin1; 
INSERT INTO `cars_to_users` (`car_id`, `user_id`) VALUES 
(1, 1), 
(2, 1), 
(3, 2), 
(4, 2), 
(5, 2); 

---

CREATE TABLE `service` (
`id` int(11) NOT NULL AUTO_INCREMENT, 
`car_plate` varchar(10) NOT NULL, 
`s_timestamp` int(10) NOT NULL, 
`price` double NOT NULL, 
PRIMARY KEY (`id`) 
) ENGINE=MyISAM DEFAULT CHARSET=latin1 AUTO_INCREMENT=111 ; 
INSERT INTO `service` (`id`, `car_plate`, `s_timestamp`, `price`) VALUES 
(1, 'ABC1234', 1312300100, 30), 
(2, 'DEF1234', 1312300100, 15), 
(3, 'QWE1234', 1312300100, 16), 
(4, 'ASD1234', 1312300100, 50), 
(5, 'ABC1234', 1312300200, 50), 
(6, 'DEF1234', 1312300200, 25), 
(7, 'QWE1234', 1312300200, 30), 
(8, 'ABC1234', 1312300300, 20), 
(9, 'ASD1234', 1312300300, 60), 
(10, 'ABC1234', 1312300400, 15), 
(11, 'ASD1234', 1312300400, 20); 

我要的是這個

car_id plate km car_plate s_timestamp price 
3 QWE1234 5000 QWE1234 1312300200 30 
3 QWE1234 5000 QWE1234 1312300100 16 
4 ASD1234 3000 ASD1234 1312300400 20 
4 ASD1234 3000 ASD1234 1312300300 60 

2行來自「s ervice「表中USER_ID的每一輛= 2的s_timestamp降序排列

ORDER BY s_timestamp LIMIT 2 DESC 

我嘗試此查詢，但給我的一切，從行‘服務’

SELECT ctu.user_id, c.car_id, c.plate, c.km, s.car_plate, s.s_timestamp, s.price 
FROM cars_to_users ctu 
LEFT JOIN cars c ON ctu.car_id = c.car_id 
LEFT JOIN service s ON c.plate = s.car_plate 
WHERE ctu.user_id = '2' 
AND c.status = 1 

如果我添加」 GROUP BYÇ .car_id」我只得到1行每車，而不是2我想

我嘗試了很多疑問，但沒有得到我想要的東西。

要記住一件事是，表中的「服務」擁有超過900萬行的數據超出例子，長大。

Answer 1

這個答案是相當複雜的。我不確定它會在你的數據庫上表現如何。

SELECT ctu.user_id, c.car_id, c.plate, c.km, s.car_plate, s.s_timestamp, s.price 
FROM cars_to_users ctu 
LEFT JOIN cars c ON ctu.car_id = c.car_id 
LEFT JOIN service s ON c.plate = s.car_plate 
JOIN 
(
    SELECT service.car_plate,max(service.s_timestamp) as s_timestamp 
    FROM service 
    JOIN 
    (
    SELECT car_plate, max(s_timestamp) as s_timestamp FROM service GROUP BY car_plate 
) as max_timestamp ON max_timestamp.car_plate = service.car_plate AND service.s_timestamp < max_timestamp.s_timestamp 
    GROUP BY service.car_plate 
) as max_2_timestamp ON s.car_plate = max_2_timestamp.car_plate AND s.s_timestamp >= max_2_timestamp.s_timestamp 
WHERE ctu.user_id = '2' 
AND c.status = 1 
ORDER BY s_timestamp DESC 

我想你可以把第2個個子查詢在臨時表中第一喜歡這個

DROP TABLE IF EXISTS max_timestamp; 
DROP TABLE IF EXISTS max_2_timestamp; 

CREATE TEMPORARY table max_timestamp SELECT car_plate, max(s_timestamp) as s_timestamp FROM service GROUP BY car_plate; 

CREATE TEMPORARY table max_2_timestamp 
(
    SELECT service.car_plate,max(service.s_timestamp) as s_timestamp 
    FROM service 
    JOIN max_timestamp ON max_timestamp.car_plate = service.car_plate AND service.s_timestamp < max_timestamp.s_timestamp 
    GROUP BY service.car_plate 
); 

SELECT ctu.user_id, c.car_id, c.plate, c.km, s.car_plate, s.s_timestamp, s.price 
FROM cars_to_users ctu 
LEFT JOIN cars c ON ctu.car_id = c.car_id 
LEFT JOIN service s ON c.plate = s.car_plate 
JOIN max_2_timestamp ON s.car_plate = max_2_timestamp.car_plate AND s.s_timestamp >= max_2_timestamp.s_timestamp 
WHERE ctu.user_id = '2' 
AND c.status = 1 
ORDER BY s_timestamp DESC; 

編輯：另一種選擇

您只需一個查詢，但我不能檢查它是否高效足夠在您的系統中。

讓我們創建一個將檢索第二最近s_timestamp每個car_plate在Service

CREATE FUNCTION LatestService (car_plate varchar(10)) 
RETURNS int(10) 
RETURN 
(SELECT s_timestamp 
FROM service s 
WHERE s.car_plate=`car_plate` 
ORDER BY s.s_timestamp desc 
LIMIT 1,1); 

然後你就可以使用函數的查詢功能。

SELECT ctu.user_id, c.car_id, c.plate, c.km, s.car_plate, s.s_timestamp, s.price 
FROM cars_to_users ctu 
LEFT JOIN cars c ON ctu.car_id = c.car_id 
LEFT JOIN service s ON c.plate = s.car_plate 
WHERE ctu.user_id = '2' 
AND c.status = 1 
AND s.s_timestamp >= LatestService(s.car_plate); 

Answer 2

排序一些ID，並添加 'HAVING COUNT（SOME_ID）< 2'

http://www.java2s.com/Code/SQL/Select-Clause/UseCOUNTGROUPandHAVING.htm

Answer 3

更換

LEFT JOIN service s ON c.plate = s.car_plate 

與

LEFT JOIN service s on s.id 
    in (SELECT s2.id FROM service s2 
     WHERE s2.car_plate=c.plate 
     ORDER BY s2.s_timestamp DESC LIMIT 2) 

我知道這將工作在MS Sql Server中，不是100％確定有關mysql。

（編輯）正如下面評論，它不。解決辦法是難看一點（但不是太糟糕），並說明如下：

http://forums.mysql.com/read.php?10,416311,416461#msg-416461