我們可以在不進行子查詢的情況下對數據進行求和嗎？

Question

我希望與利率和他們的差異作爲保證金

相關的合同我想這樣做總和在SQL Server中沒有自我加入子查詢中的表。

我的架構設置如下：

合同

ContractId relatedContractId Discriminator 
----------------------------------------------------- 
8041  8040    VendorContract 
8040  8041    CustomerContract 
8042  NULL    CustomerContract 
8043  8044    CustomerContract 
8044  8043    VendorContract 

價格

RateId RatePerUnit ContractId 
--------------------------------- 
8052 120.00  8041 
8053 123.00  8041 
8050 121.00  8040 
8051 127.00  8040 
8052 120.00  8042 
8053 137.00  8042 
8054 102.00  8043 
8055 100.00  8044 

預期成果是

CContract  VContract Marging 
------------------------------------ 
8040   8041   5.00 
8042   Null   257.00 
8043   8044   2.00 

我已經實現了正確的結果，下面的查詢使用了子查詢，但我需要在不使用子查詢的情況下執行此操作。

SELECT cts.ContractId, 
     cts.RelatedContractId, 
     (ISNULL(SUM(r.RatePerUnit),0) - ISNULL(vr.VendorContractRate,0)) AS Margin 
FROM Contracts cts 
     LEFT OUTER JOIN Contracts vcts 
      ON cts.RelatedContractId = vcts.ContractId 
     LEFT OUTER JOIN Rates r 
      ON cts.ContractId = r.ContractId 
     LEFT OUTER JOIN 
     ( SELECT c.ContractId, 
        ISNULL(SUM(r.RatePerUnit),0) VendorContractRate 
      FROM Contracts c 
        LEFT OUTER JOIN Rates r 
         ON r.ContractId = c.contractId 
      WHERE c.Discriminator = 'VendorContract' 
      GROUP BY c.ContractId 
     ) vr 
      ON cts.RelatedContractId = vr.ContractId   
WHERE cts.Discriminator = 'CustomerContract' 
GROUP BY cts.ContractId, cts.RelatedContractId, vr.VendorContractRate; 

我試圖重寫此查詢，而無需使用子查詢，如下所示：

SELECT vc.ContractId, 
     SUM(r.RatePerUnit), 
     SUM(vr.RatePerUnit) 
FROM Contracts c 
     LEFT OUTER JOIN Contracts vc 
      ON c.RelatedContractId = vc.ContractId 
     LEFT OUTER JOIN Rates r 
      ON r.ContractId= c.ContractId 
     INNER JOIN Rates vr 
      ON vr.ContractId = vc.ContractId 
WHERE c.Discriminator = 'CustomerContract' 
AND  c.ContractStatus = 0 
GROUP BY vc.ContractId; 

不幸的是，這是我的複製結果，所以它是不正確的。對於多種費率，它將費率乘以存在的費率數量。所以我得到的結果是：

CContract  VContract Marging 
------------------------------------ 
8040   8041   10.00  ---- in this case 496-486(248-243) 
8042   Null   514.00  
8043   8044   2.00   

Answer 1

我看不出這樣做沒有某種形式的子查詢的簡單方式，但也沒有理由儘量避免子查詢。你已經列舉了希望避免子查詢的性能原因，但這不是一個有效的原因，SQL是一種聲明性語言，即你告訴優化者你想要什麼而不是如何獲得它，所以僅僅因爲你使用了子查詢並不意味着你是改變計劃的必需品。

雖然不需要刪除子查詢來提高性能，但這並不是說您的查詢性能仍然無法提高。這可以通過刪除不必要的連接來完成。下面應該有更好的表現：

WITH SummedRates AS 
( SELECT ContractID, RatePerUnit = SUM(RatePerUnit) 
    FROM Rates 
    GROUP BY ContractID 
) 
SELECT c.ContractID, 
     c.RelatedContractID, 
     Margin = ISNULL(r.RatePerUnit, 0) - ISNULL(r2.RatePerUnit, 0) 
FROM Contracts AS c 
     LEFT JOIN SummedRates AS r 
      ON r.ContractId = c.ContractId 
     LEFT JOIN SummedRates AS r2 
      ON r2.ContractId = c.RelatedContractId 
WHERE c.Discriminator = 'CustomerContract' 

FULL工作演示

DECLARE @Contracts TABLE (ContractId INT, relatedContractId INT, Discriminator VARCHAR(20)); 
INSERT @Contracts (ContractId, relatedContractId, Discriminator) 
VALUES 
    (8041, 8040, 'VendorContract'), 
    (8040, 8041, 'CustomerContract'), 
    (8042, NULL, 'CustomerContract'), 
    (8043, 8044, 'CustomerContract'), 
    (8044, 8043, 'VendorContract'); 

DECLARE @Rates TABLE (RateId INT, RatePerUnit DECIMAL(5, 2), ContractId INT); 
INSERT @Rates (RateId, RatePerUnit, ContractId) 
VALUES 
    (8052, 120.00, 8041), 
    (8053, 123.00, 8041), 
    (8050, 121.00, 8040), 
    (8051, 127.00, 8040), 
    (8052, 120.00, 8042), 
    (8053, 137.00, 8042), 
    (8054, 102.00, 8043), 
    (8055, 100.00, 8044); 

WITH SummedRates AS 
( SELECT ContractID, RatePerUnit = SUM(RatePerUnit) 
    FROM @Rates 
    GROUP BY ContractID 
) 
SELECT c.ContractID, 
     c.RelatedContractID, 
     Margin = ISNULL(r.RatePerUnit, 0) - ISNULL(r2.RatePerUnit, 0) 
FROM @Contracts AS c 
     LEFT JOIN SummedRates AS r 
      ON r.ContractId = c.ContractId 
     LEFT JOIN SummedRates AS r2 
      ON r2.ContractId = c.RelatedContractId 
WHERE c.Discriminator = 'CustomerContract';