mysql - 从一张表中获取不同的行和*

Question

我正在尝试获取一张汽车表格，其中三行与其他三列(品牌、型号和组别)相关，而我只想按型号获取一辆汽车。

这是 MySQL 表的图像:

您将看到三行具有相同的 model_id(model_id 是另一个表的外键，另一个表称为模型)

用于获取这些汽车的 SQL 查询是:

SELECT *
FROM gm_cars AS cars
INNER JOIN gm_cars_makes AS makes
   ON (cars.make_id = makes.make_id)
INNER JOIN gm_cars_models AS models
   ON (cars.model_id = models.model_id)
INNER JOIN gm_cars_groups AS groups
   ON (cars.group_id = groups.group_id) AND
       makes.make_visible = 1
ORDER BY cars.model_id;

但我希望为一个模型获取一行，这里有一个例子(我使用过Photoshop):

有些像:SELECT *, DISTINCT(model_id) FROM cars

Answer 1

如果您仍然想返回所有列，您可以创建子查询以仅返回每个模型一辆汽车，然后像以前一样编写查询:

SELECT * FROM gm_cars AS cars 
INNER JOIN (SELECT model_id, MAX(car_Id) AS car_Id FROM gm_cars GROUP BY model_id) AS grp_cars ON grp_cars.car_Id = cars.car_Id
INNER JOIN gm_cars_makes AS makes ON (cars.make_id = makes.make_id) 
INNER JOIN gm_cars_models AS models ON (cars.model_id = models.model_id) 
INNER JOIN gm_cars_groups AS groups ON (cars.group_id = groups.group_id) AND makes.make_visible = 1 ORDER BY cars.model_id;

您还可以在主查询中添加GROUP BY，并向所有其他列添加聚合函数。但它可以返回具有相同型号的不同汽车的列:

SELECT cars.model_id,
    MAX(car_passengers),
    MAX(car_suitcases),
    ....
FROM gm_cars AS cars 
INNER JOIN (SELECT model_id, MAX(car_Id) AS car_Id FROM gm_cars GROUP BY model_id) AS grp_cars ON grp_cars.car_Id = cars.car_Id
INNER JOIN gm_cars_makes AS makes ON (cars.make_id = makes.make_id) 
INNER JOIN gm_cars_models AS models ON (cars.model_id = models.model_id) 
INNER JOIN gm_cars_groups AS groups ON (cars.group_id = groups.group_id) AND makes.make_visible = 1 
GROUP BY cars.model_id
ORDER BY cars.model_id;