从一个表中选择一个给定年份的所有月份的记录，其中包含第二个表中的记录

Question

我的数据库中有两个表：

• MembershipInstallments (ProjectId, AllotmentId, InstallmentId, EntryDate, AmountPaid)
• Memberships (ProjectId, AllotmentId, ClientId, ClientName, RegistrationNo)

我想选择客户在一年中按月支付的款项。以及当年年初之前支付的金额。我想要的结果集是

假设 2019 年：

ClientName, RegistrationNumbers, PreviouslyPaidAmount (i.e. all amounts paid in 2018), AmountPaidInJuly 2019, AmountPaidInAugust2019. ..... AmountPaidIn Jun2020

其中月份是来自MembershipInstallments 表的EntryDate。

我是这样尝试的，但是对于大数据集来说时间太长了：

SELECT 
    ClientName, RegistrationNo,
    (SELECT ISNULL(SUM(AmountPaid),0)
     FROM MembershipInstallments 
     WHERE ProjectId = Membership.ProjectId 
       AND AllotmentId = Membership.AllotmentId 
       AND EntryDate < @fromDate) ASPreviouslyPaid,
    (SELECT ISNULL(SUM(AmountPaid), 0)
     FROM MembershipInstallments 
     WHERE ProjectId = Membership.ProjectId 
       AND AllotmentId = Memberhsip.AllotmentId 
       AND (MONTH(EntryDate) = 7) AND (YEAR(EntryDate) = YEAR(@fromDate)) AS JulyPayment
FROM 
    Memberships 
WHERE 
    ProjectId = @projectId

我们将不胜感激。

Answer 1

标量子查询往往被严重优化。在您的情况下（相同的连接条件），您可以简单地利用 条件聚合：

SELECT ms.ClientName,ms.RegistrationNo,
   Sum(CASE WHEN mi.EntryDate<@fromDate THEN mi.AmountPaid ELSE 0 end) AS PreviouslyPaid,
   Sum(CASE WHEN (Month(mi.EntryDate) = 7) AND (Year(mi.EntryDate) = Year(@fromDate)) THEN mi.AmountPaid ELSE 0)
FROM Memberships AS ms
LEFT JOIN MembershipInstallments AS mi -- don't know if Outer join is really needed
  ON mi.ProjectId=ms.ProjectId
  AND mi.AllotmentId=ms.AllotmentId
WHERE ms.ProjectId=@projectId

您也许可以在加入之前进行聚合，即在 CTE 中以进一步提高性能：

WITH cte AS
 (
   SELECT  
      ProjectId, AllotmentId,
      Sum(CASE WHEN EntryDate<@fromDate THEN AmountPaid ELSE 0 END) AS PreviouslyPaid,
      Sum(CASE WHEN (Month(EntryDate) = 7) AND (Year(EntryDate) = Year(@fromDate)) THEN AmountPaid ELSE 0 END) AS JulyPayment
   FROM MembershipInstallments 
   WHERE ProjectId=@projectId
   GROUP BY ProjectId, AllotmentId
 )
SELECT ms.ClientName, ms.RegistrationNo, cte.PreviouslyPaid, cte.JulyPayment
FROM Memberships AS ms
JOIN cte
  ON cte.ProjectId=ms.ProjectId
  AND cte.AllotmentId=ms.AllotmentId
WHERE ms.ProjectId=@projectId

在这两种情况下，仔细检查结果是否正确（取决于这些表之间的实际关系）