Select 针对给定年份的所有月份的记录形成一个表，其中记录来自第二个表

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 select 客户在一年内按月付款。 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MembershipInstallments表中的EntryDate 。

我是这样尝试的，但是对于大型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

任何帮助将不胜感激。

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

您可能能够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，请仔细检查结果是否正确（取决于这些表之间的实际关系）