怎么＆lt;＆gt;在SQL工作？

Question

我有模拟考试，其中一个问题是

哪个供应商名称没有发送红色部分？

数据库架构如下

 Supplier (SupplierName, City) 
 Part(PartName, Color, Weight) 
 Shipment(SupplierName, PartName, Date) 
 Shipment(SupplierName) is a F.K. onto Supplier(SupplierName) 
 Shipment(PartName) is a F.K. onto Part(PartName)

我提出的查询是

SELECT S.SupplierName
FROM Supplier as S
JOIN Shipment as SH on S.SupplierName = SH.SupplierName
JOIN Part as P on SH.PartName = P.PartName
WHERE P.Color <> 'Red'

我的问题是，我使用＆lt;＆gt;正确的方法？

Answer 1

您是否发现供应商至少提供了一部分不是红色的部件。

他们也可能提供红色部件，即使是与非红色部件相同的货物。

您可以使用

SELECT S.SupplierName
FROM   Supplier AS S
WHERE  NOT EXISTS (SELECT *
                   FROM   Shipment AS SH
                          JOIN Part AS P
                            ON SH.PartName = P.PartName
                   WHERE  S.SupplierName = SH.SupplierName
                          AND P.Color = 'Red')