Question

我有三张桌子：

帐户：

AccountId | AccountEmail

PurchasedProducts：

ProductName | AccountId | ProductTypeId

ProductTypes：

ProductTypeId | ProductTypeName

我想创建一个查询，计算每个帐户每种产品类型的已购买产品数量。看起来应该是这样的：

AccountEmail  | ProductTypeName A | ProductTypeName B | ProductTypeName C
-------------------------------------------------------------------------
peter@test.nl | 0                 | 12                | 1

我无法弄清楚如何进行此查询...任何人都可以帮忙吗？提前谢谢！

Answer 1

这样的东西会起作用

SELECT accountemail, 
       Sum(CASE 
             WHEN producttypename = 'ProductTypeName A' THEN 1 
             ELSE 0 
           END) AS 'ProductTypeName A', 
       Sum(CASE 
             WHEN producttypename = 'ProductTypeName B' THEN 1 
             ELSE 0 
           END) AS 'ProductTypeName B', 
       Sum(CASE 
             WHEN producttypename = 'ProductTypeName C' THEN 1 
             ELSE 0 
           END) AS 'ProductTypeName C' 
FROM   purchasedproducts p 
       INNER JOIN producttypes ot 
               ON p.producttypeid = pt.producttypeid 
       INNER JOIN account a 
               ON a.accountid = p.accountid 
WHERE  producttypename IN ( 'ProductTypeName A', 'ProductTypeName B', 
                            'ProductTypeName C' ) 
GROUP  BY accountemail

Answer 2

以下（基于@ VR46的回答）将给出正确的值，但不是OP提供的确切表格格式。我认为，这应该足以满足大多数用途，如果需要每列producttype格式，可以使用Excel或其他查询创建数据透视表。

SELECT accountemail, producttypename, COUNT(*)
FROM   purchasedproducts p 
       INNER JOIN producttypes ot 
               ON p.producttypeid = pt.producttypeid 
       INNER JOIN account a 
               ON a.accountid = p.accountid 
GROUP  BY accountemail, producttypename

查询计算已连接表中的所有项目

2 个答案: