MYSQL通过两个键内连接两个表

我正在执行查询以返回存储在 sb_carts 表中的所有用户购物车。存储在 sb_carts 中的产品信息通过两个键 Product_sku 和 school_id 引用。它需要参考两者来返回具有独特库存水平等的独特产品。

当我执行以下查询时，它返回一行，我期望 3 行。 我尝试将内部联接分成两个单独的联接，但这仍然只返回 1 个结果。仅在一个键上加入可以获得所需的结果，但可能会重新调整错误的产品。左连接返回 3 行，但某些数据缺少特定于产品的数据

这是我正在做的事情的一个简化示例

SELECT sb_carts.product_sku
FROM sb_carts 
INNER JOIN sb_products ON sb_products.sku = sb_carts.product_sku 
AND sb_products.school_id = sb_carts.school_id
WHERE sb_carts.order_id = 0 
AND sb_carts.user_id = 2 
GROUP BY sb_carts.cart_id
  

完整查询看起来像

SELECT COUNT(DISTINCT sb_carts.cart_id) as quantity, 
sb_carts.* FROM sb_carts 
INNER JOIN sb_children ON sb_children.child_id = sb_carts.child_id 
INNER JOIN sb_school_entities ON sb_school_entities.school_id   = sb_children.school_id 
INNER JOIN sb_products ON sb_products.sku = sb_carts.product_sku 
AND sb_products.school_id = sb_carts.school_id LEFT JOIN sb_houses ON sb_children.house_id = sb_houses.id 
LEFT JOIN sb_refund_cart ON sb_carts.cart_id = sb_refund_cart.cart_id 
WHERE sb_carts.order_id = 0 
AND sb_carts.user_id = 2 
GROUP BY sb_carts.child_id, sb_carts.product_sku, sb_carts.school_id 
ORDER BY sb_children.dob_year, sb_children.dob_month, sb_children.dob_day ASC
  

问题最有可能是GROUP BY。即使购物车中有多个产品，这也只会为每个购物车 ID 返回一条记录。要获得您想要的，请尝试以下操作：

SELECT sb_carts.cart_id, sb_carts.product_sku
FROM sb_carts 
INNER JOIN sb_products ON sb_products.sku = sb_carts.product_sku 
AND sb_products.school_id = sb_carts.school_id
WHERE sb_carts.order_id = 0 
AND sb_carts.user_id = 2 
ORDER BY sb_carts.cart_id
  

这将返回两列（购物车 ID 和 SKU）而不是一列，并且一个购物车 ID 的所有商品将在查询中显示为连续行。