如何在 MySQL 的左连接中获取关联行的计数?
我有两个表,一个 vehicle
表,其中包含列:
I have two tables, a vehicle
table with columns:
id
股票
年份
制作
模型
和一个带有列的 images
表:
and an images
table with columns:
id
vehicle_id
名称
标题
默认 tinyint(1)
我正在尝试列出车辆的信息、默认图像以及车辆拥有的图像总数.目前我正在使用以下 SELECT
语句:
I am trying to list the vehicle's information, its default image, and a total count of images the vehicle has. Currently I am using the following SELECT
statement:
SELECT vehicle.id, vehicle.stock, vehicle.year,
vehicle.make, vehicle.model, images.name,
COUNT(images.id)
FROM vehicle
LEFT JOIN images
ON vehicle.id = images.vehicle_id
我最初使用的是:
ON vehicle.id = images.vehicle_id AND images.default = 1
但是根据数据库中是否存在默认图像,图像计数将仅为 1 或 0.我曾尝试使用 UNION
和其他 SELECT
语句,但我仍然无法获得正确的结果.我需要使用两个 SELECT
语句还是有其他方法可以使用 JOIN
或 UNION
来处理它?</p>
but then the images count would only be 1 or 0 depending if there was a default image in the database. I have tried using UNION
and other SELECT
statements but I am still unable to get a proper result. Do I need to use two SELECT
statements or is there another way to handle it with JOIN
or UNION
?
推荐答案
SELECT
`vehicle`.`id`,
`vehicle`.`stock`,
`vehicle`.`year`,
`vehicle`.`make`,
`vehicle`.`model`,
`images`.`name`,
(
SELECT COUNT(*)
FROM `images`
WHERE `vehicle_id` = `vehicle`.`id`
) AS `image_count`
FROM `vehicle`
LEFT JOIN `images`
ON `images`.`vehicle_id` = `vehicle`.`id`
WHERE `images`.`default`
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