如何获取产品以及每次购买的数量与一个SQL查询？

Question

Buy有一个外键product_id。

所以除了SELECT * FROM products;我们有兴趣得到每个产品的购买数量。

Answer 1

加入

SELECT Products.*, COUNT(Buy.ID) AS Bought 
FROM products 
    LEFT OUTER JOIN Buy ON products.ID = Buy.product_id 
GROUP BY Buy.product_id 

子查询

SELECT 
    Products.*, 
    (SELECT COUNT(ID) FROM Buy WHERE product_id = Products.ID) AS Bought 
FROM products 

Answer 2

SELECT p.*,COUNT(b.product_id) FROM products p 
INNER JOIN buy b ON p.id=b.product_id 
GROUP BY b.product_id 

这就是我所能提供的所有信息。如果上述不起作用，两者的表格结构都会有帮助。

Answer 3

线沿线的东西：

SELECT p.*, COUNT(buy.product_id) FROM product p INNER JOIN buy ON buy.product_id = p.id GROUP BY buy.product_id 

应该做的伎俩。