如何使用一个SQL查询获取产品和每个购买的数量？

Question

Buy有一个外键product_id。

所以除了SELECT * FROM products;之外，我们还有兴趣了解每个产品的购买数量。

Answer 1

有些事情：

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

应该这样做。

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

这就是我发布的所有信息。如果上述方法不起作用，两者的表结构将有助于实现。

Answer 3

<强>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

<强>子查询

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