访问 SQL 查询返回错误的计数字段值答案

【问题标题】：Access SQL Query Returning Wrong Value for Count Field访问 SQL 查询返回错误的计数字段值
【发布时间】：2014-04-10 02:33:58
【问题描述】：

我正在尝试进行SQL 查询，获取客户姓名加上c 列，这是Count 与Customers.[Customer ID] = Referrals.[Referred From] 和Referrals.[Used Our Service] = True 连接到推荐的行数

第二列是c2，它是Count 与Customers.[Customer ID] = Referrals.[Referred From] 和Referrals.[Valid Referral] = True 连接到引荐的行数

此查询工作正常，但在c2 列中返回错误的数字。它应该为 1 时返回 2。

SELECT 
Customers.[Customer ID], Customers.[First Name], Customers.[Last Name], Count(r.[Valid Referral]) AS c, Count(rr.[Used Our Service]) AS c2
FROM (Customers 
INNER JOIN Referrals r ON Customers.[Customer ID] = r.[Referred From] AND (r.[Valid Referral])=True)
INNER JOIN Referrals rr ON Customers.[Customer ID] = rr.[Referred From] AND (rr.[Used Our Service])=True
WHERE (r.[Valid Referral])=True
GROUP BY Customers.[Customer ID], Customers.[First Name], Customers.[Last Name]

客户表：

推荐表：

结果表：

【问题讨论】：

标签： sql ms-access count ms-access-2010

【解决方案1】：

我建议不要将同一个表加入两次，而是将SUM 与Iif 一起使用，如下所示：

SELECT 
Customers.[Customer ID], 
Customers.[First Name], 
Customers.[Last Name], 
SUM(Iif(r.[Valid Referral] = True, 1, 0)) AS c, 
Sum(Iif(r.[Used Our Service] = True, 1, 0)) AS c2
FROM Customers 
INNER JOIN Referrals r ON Customers.[Customer ID] = r.[Referred From] 
WHERE (r.[Valid Referral])=True
GROUP BY Customers.[Customer ID], Customers.[First Name], Customers.[Last Name]

【讨论】：