按 memberID 计算最近的续订

Question

我有一个按日期跟踪会员续订的订阅表。更新适用于日历年，但会员最早可以在 10 月 1 日更新，在这种情况下，他们的有效期将持续到下一年的 12 月 31 日。因此，可以在一月份续订，然后在同年十月再次续订。我按月报告会员总数，我想避免将其计为 2 个会员。

每条记录都有一个唯一的prodID，但由于上面的续订选项，memberID 的记录可以超过 1 条。 payDate是交易日期

我的声明是：

$sql = "SELECT 
            EXTRACT(MONTH FROM payDate) as month, 
            EXTRACT(YEAR FROM payDate) as year, 
            count(*) 
            FROM 
                memberDues
            WHERE payDate >= $lastYear-10-01
            GROUP BY 
                month, 
                year
            ORDER BY 
                year ASC, 
                month ASC";

我得到这样的输出（未格式化）：

Member dues paid by month  
October         46  
November        30  
December        99  
January         42  
February         8  
March            9  
April            4  
May              1  
June             3  
Member Total:  242

如何修改选择语句以避免在报告期间重复续订？

Answer 1

您需要按 memberID 分组，以使一个会员续订不被重复。

  SELECT year, month, count(memberID) FROM (
  SELECT memberID,
  EXTRACT(MONTH FROM payDate) as month, 
    EXTRACT(YEAR FROM payDate) as year, 
    count(*) 
    FROM 
        memberDues
    WHERE payDate >= $lastYear-10-01
    GROUP BY 
        memberID,
        month, 
        year
    ORDER BY 
        year ASC, 
        month ASC";
    )TMP GROUP BY year, month

Answer 2

计算每个月不同的 memberID 应该可以完成这项工作：

                SELECT 
                EXTRACT(MONTH FROM payDate) as month, 
                EXTRACT(YEAR FROM payDate) as year, 
                count(DISTINCT memberID) 
                FROM 
                    memberDues
                WHERE payDate >= $lastYear-10-01
                GROUP BY 
                    month, 
                    year
                ORDER BY 
                    year ASC, 
                    month ASC