重构SQL查询以将结果返回到行而不是列中

我有一个SQL查询需要重构。基本上，查询获取指定客户订购的所有ProductType。问题是结果以列而不是行的形式返回。这需要以另一种方式进行更改，以使查询更通用

那么这就是查询返回的结果：

Name   ProductType1   ProductType2   ProductType3
--------------------------------------------------
Marc   PT09           P15            PT33

Name ProductType
----------------
Marc PT09
Marc P15
Marc PT33

SELECT 
      CustomerData.Name as Name
      Product1.productType as ProductType1,
      Product2.productType as ProductType2,
      Product3.productType as ProductType3
FROM
    (SELECT ProductID, Name
            FROM 
                Customer 
                Orders
      WHERE Customer.ID = 111
    ) as CustomerData

LEFT JOIN (SELECT DISTINCT CP.ProductID as ProductID,
                           PC.Type as ProductType
           FROM 
                CustomerProduct CP,
                ProductCategory PC
           WHERE
                PC.Category = 'A'
                AND CP.ProductCategoryID = PC.ID
           )  as Product1
           on CustomerData.ProductID = Product1.ProductID

LEFT JOIN (SELECT DISTINCT CP.ProductID as ProductID,
                           PC.Type as ProductType
           FROM 
                CustomerProduct CP,
                ProductCategory PC
           WHERE
                PC.Category = 'B'
                AND CP.ProductCategoryID = PC.ID
           )  as Product2
           on CustomerData.ProductID = Product1.ProductID

LEFT JOIN (SELECT DISTINCT CP.ProductID as ProductID,
                           PC.Type as ProductType
           FROM 
                CustomerProduct CP,
                ProductCategory PC
           WHERE
                PC.Category = 'C'
                AND CP.ProductCategoryID = PC.ID
           )  as Product3
           on CustomerData.ProductID = Product1.ProductID

这就是它应该的样子：

Name   ProductType1   ProductType2   ProductType3
--------------------------------------------------
Marc   PT09           P15            PT33

Name ProductType
----------------
Marc PT09
Marc P15
Marc PT33

SELECT 
      CustomerData.Name as Name
      Product1.productType as ProductType1,
      Product2.productType as ProductType2,
      Product3.productType as ProductType3
FROM
    (SELECT ProductID, Name
            FROM 
                Customer 
                Orders
      WHERE Customer.ID = 111
    ) as CustomerData

LEFT JOIN (SELECT DISTINCT CP.ProductID as ProductID,
                           PC.Type as ProductType
           FROM 
                CustomerProduct CP,
                ProductCategory PC
           WHERE
                PC.Category = 'A'
                AND CP.ProductCategoryID = PC.ID
           )  as Product1
           on CustomerData.ProductID = Product1.ProductID

LEFT JOIN (SELECT DISTINCT CP.ProductID as ProductID,
                           PC.Type as ProductType
           FROM 
                CustomerProduct CP,
                ProductCategory PC
           WHERE
                PC.Category = 'B'
                AND CP.ProductCategoryID = PC.ID
           )  as Product2
           on CustomerData.ProductID = Product1.ProductID

LEFT JOIN (SELECT DISTINCT CP.ProductID as ProductID,
                           PC.Type as ProductType
           FROM 
                CustomerProduct CP,
                ProductCategory PC
           WHERE
                PC.Category = 'C'
                AND CP.ProductCategoryID = PC.ID
           )  as Product3
           on CustomerData.ProductID = Product1.ProductID

这是我简化了一点的查询：

Name   ProductType1   ProductType2   ProductType3
--------------------------------------------------
Marc   PT09           P15            PT33

Name ProductType
----------------
Marc PT09
Marc P15
Marc PT33

SELECT 
      CustomerData.Name as Name
      Product1.productType as ProductType1,
      Product2.productType as ProductType2,
      Product3.productType as ProductType3
FROM
    (SELECT ProductID, Name
            FROM 
                Customer 
                Orders
      WHERE Customer.ID = 111
    ) as CustomerData

LEFT JOIN (SELECT DISTINCT CP.ProductID as ProductID,
                           PC.Type as ProductType
           FROM 
                CustomerProduct CP,
                ProductCategory PC
           WHERE
                PC.Category = 'A'
                AND CP.ProductCategoryID = PC.ID
           )  as Product1
           on CustomerData.ProductID = Product1.ProductID

LEFT JOIN (SELECT DISTINCT CP.ProductID as ProductID,
                           PC.Type as ProductType
           FROM 
                CustomerProduct CP,
                ProductCategory PC
           WHERE
                PC.Category = 'B'
                AND CP.ProductCategoryID = PC.ID
           )  as Product2
           on CustomerData.ProductID = Product1.ProductID

LEFT JOIN (SELECT DISTINCT CP.ProductID as ProductID,
                           PC.Type as ProductType
           FROM 
                CustomerProduct CP,
                ProductCategory PC
           WHERE
                PC.Category = 'C'
                AND CP.ProductCategoryID = PC.ID
           )  as Product3
           on CustomerData.ProductID = Product1.ProductID

---

因此，我一直在考虑将连接拆分为一个单独的存储过程，然后调用它，因为我需要更多的ProductType，但我似乎无法让它正常工作。有没有人能想出办法让它工作起来？

在专栏中做事通常要困难得多

假设客户、产品和订单都是标准化的表，您不需要做任何事情，只需要：

SELECT C.customer_name
     , P.product_type
FROM Customers C
  JOIN Orders O
    ON O.customer_id=C.customer_id
  JOIN Products P
    ON O.product_id=P.product_id
WHERE C.ID = 111

---

如果这不起作用，请列出相关表的结构。

我假设您的表看起来像这样

顾客

id | name
11 | Marc

产品

id | type
21 | PT09
22 | P15
23 | PT33

命令

id | id_customer | id_product | quantity
31 | 11          | 21         | 4
32 | 11          | 22         | 6
33 | 11          | 23         | 8

那么你的问题是

SELECT 
    a.name,
    c.type
FROM 
    Customer a
LEFT JOIN 
    Orders b ON b.id_customer = a.id
LEFT JOIN 
    Products c ON c.id = b.id_product 

---

在执行查询之前，是否知道产品类型的数量？如果是这样的话，您可以使用多个联合动态创建SQL。+1是的，就是这样做的。它可能只需要

LEFT JOIN

而不是

JOIN

，这取决于他的数据和他想要显示的内容。或者，如果客户有许多相同产品的订单，而您只想看到其中任何一个（订单）的一行，则可以使用

分组方式。如果他想显示或过滤ProductCategory，也可以再加入一次。但这是一条路要走。此外，查询看起来简单而优雅：不到10行代码，而不是40多行复杂的4个子查询。