Question

products(id, name)
categories(id, name, product_id)

我有一个示例代码：

products(1, 'Apple')

和类别

categories(1, 'Iphone', 1)
categories(2, 'Ipad', 1)
categories(3, 'Ipod', 1)

并查询：

SELECT pr.id, cat.name, pr.name 
FROM `products` as pr
LEFT JOIN `categories` as cat USING(id)
GROUP BY pr.id

但结果是

1, "Iphone", "Apple"

并且Ipad, Ipod没有显示，如何修复它？

 1, "Iphone, Ipad, Ipod", "Apple"

Answer 1

您的JOIN条件正在尝试加入两个ID列，这不是关系。它应该将product.id加入category.produt_id

SELECT pr.id, cat.name, pr.name 
FROM `products` as pr
LEFT JOIN `categories` as cat ON pr.id = cat.product_id
GROUP BY pr.id

编辑：我意识到你只需要一个类别连接的结果。您需要在选择列表中使用GROUP_CONCAT函数：

SELECT pr.id, GROUP_CONCAT(cat.name), ...