更高效的 MySQL 子查询？

Question

我在用子查询来处理查询时遇到了麻烦。如果愿意，请继续：

样本数据：

CREATE TABLE users (
    user_id INT(10) NOT NULL AUTO_INCREMENT,
    username VARCHAR(64),
    PRIMARY KEY (user_id)
);

CREATE TABLE cars {
    car_id INT(10) NOT NULL AUTO_INCREMENT,
    user_id INT(10),
    caryear YEAR(4),
    carmaker VARCHAR(32),
    carmodel VARCHAR(32),
    PRIMARY KEY (car_id, user_id)
    FOREIGN KEY(`user_id`) references users(`user_id`)
) ENGINE=InnoDB;    

INSERT INTO users (user_id, name) VALUES (1,'Bob'),(2,'John'),(3,'Sally');
INSERT INTO cars (user_id, caryear, carmaker, carmodel) VALUES
(1,'2004','Audi','A4'),
(1,'2006','Toyota','Camry'),
(1,'2014','Jeep','CJ'),
(2,'1998','Acura','CL'),
(2,'2014','Honda','Accord'),
(3,'2011','Jeep','Rubicon')

好的，如果我想获取用户及其汽车的列表，我可以这样做：

SELECT
  user_id,
  username,
  (SELECT GROUP_CONCAT(CONCAT(CarYear,' ',CarMaker,' ',CarModel))
   FROM cars
   WHERE cars.user_id = users.user_id
  ) AS Cars
FROM users;

但是，例如，我如何获得拥有 2004-2014 吉普车的用户列表？

我想出了这个，但是我确信还有更优雅的方法：

SELECT
  user_id,
  username,
  (SELECT GROUP_CONCAT(CONCAT(CarYear,' ',CarMaker,' ',CarModel))
   FROM cars
   WHERE cars.user_id = users.user_id
   AND CarMaker = 'Jeep'
   AND CarYear BETWEEN 2004 AND 2014
  ) AS Cars
FROM users
HAVING Cars is not null;

此解决方案的问题在于，它不显示拥有 2004-2014 吉普车的人所拥有的其他汽车。

有什么建议吗？

Answer 1

因为这是一个多对多的关系，你实际上需要将cars 分成两个表。第一个表将与现在的cars 相同，除了从中删除user_id。第二个表（称为user_car）有两列：user_id 和car_id。

一旦你这样做了，查询就很简单了：

SELECT user_id FROM user_car WHERE car_id IN
    (SELECT car_id FROM cars
   WHERE CarMaker = 'Jeep'
   AND CarYear BETWEEN 2004 AND 2014
  )

如果您需要直接从users 中提取数据，请将查询展开为：

SELECT user_id, username FROM users WHERE user_id IN
  (SELECT user_id FROM user_car WHERE car_id IN
    (SELECT car_id FROM cars
   WHERE CarMaker = 'Jeep'
   AND CarYear BETWEEN 2004 AND 2014
  ))

Answer 2

INNER JOIN 可以解决问题。

SELECT u.* FROM users u
INNER JOIN cars c ON c.user_id = u.user_id
WHERE CarMaker = 'Jeep' AND CarYear BETWEEN 2004 AND 2014 

Answer 3

为拥有 Jeep 2004-2014 的任何用户显示用户及其所有汽车的列表：

SELECT
  u.user_id,
  u.username,
  GROUP_CONCAT(CONCAT(c.CarYear,' ',c.CarMaker,' ',c.CarModel)) AS Cars
FROM users u
INNER JOIN cars c USING (user_id)
INNER JOIN (
  SELECT DISTINCT user_id FROM cars
  WHERE c.CarMaker = 'Jeep' 
    AND c.CarYear BETWEEN 2004 AND 2014) AS j USING (user_id)
GROUP BY u.user_id, u.username;