为什么我的SQL查询返回重复结果？

Question

SQL在下面 - 每个结果出现3次而不是仅仅一次。

SELECT Consignments.LegacyID, TripDate, CollectionName, DeliveryName, Pallets, Weight, BaseRate, Consignments.FuelSurcharge, AdditionalCharges, BaseRate * Quantity AS 'InvoiceValue', Consignments.Customer, InvoiceNumber, 
     CASE 
      WHEN child.LegacyID = Consignments.Customer THEN child.LegacyID 
      WHEN parent.LegacyID = Consignments.Customer THEN parent.LegacyID 
      ELSE this.LegacyID 
     END AS 'InvoiceAcc' 
FROM SageAccount this 
    LEFT JOIN SageAccount parent on parent.LegacyID = this.InvoiceAccount 
    LEFT JOIN SageAccount child on this.LegacyID = child.InvoiceAccount 
    JOIN Consignments on (Consignments.Customer = this.LegacyID AND this.Customer = 'True') 
        OR (Consignments.Customer = parent.LegacyID AND parent.Customer = 'True') 
        OR (Consignments.Customer = child.LegacyID AND child.Customer = 'True') 
WHERE (this.LegacyID = @Customer) AND (TripDate BETWEEN @fromdate AND @todate) AND (InvoiceNumber IS NOT NULL) 

的SQL是给我的另一个类似的查询，但这个时候，我已经修改了它尝试使用它，现在我做的查询，所以我假设我做的事笨。

非常感谢。

Answer 1

JOIN Consignments on (Consignments.Customer = this.LegacyID AND this.Customer = 'True') 
OR (Consignments.Customer = parent.LegacyID AND parent.Customer = 'True') 
OR (Consignments.Customer = child.LegacyID AND child.Customer = 'True') 

我猜ü应使用 “this.InvoiceAccount”，而不是this.LegacyID

Answer 2

可能是因为您的左连接每个父行有3个子行。 做一个select *来查看你的结果在相乘的行中会有不同的结果。