多次连接表的 LINQ 问题

Question

我继承了一个模式，我需要使用它来处理一些sql。它是为了展示产品的变化，例如毛衣的颜色和尺寸变化。该架构有 1 个产品表：

TABLE tbl_Product

[ProductID] [int],
[Quantity] [int],
[Title] [nvarchar](500),
[Description] [varchar](max),
[Price] [money]  

等...

另一个表作为变体的链接表

TABLE tbl_ProductVariation

[ProductVariationID] [int],
[ProductID] [int] ,
[VariationID] [int]  

和变体表

TABLE tbl_Variation，

[VariationID] [int],
[VariationTypeID] [int] NOT NULL,
[USTitle] [nvarchar](150) NULL,
[UKTitle] [nvarchar](150) NULL

因此变体值可以包含取决于variationtypeid的颜色或尺寸

那么为什么这个查询会失败??

SELECT [t4].[ProductVariationID], [t5].[UKTitle] AS [Size], 
       [t6].[UKTitle] AS [Colour], [t0].[Title]
FROM [dbo].[tbl_Product] AS [t0]
INNER JOIN [dbo].[tbl_ProductCategory] AS [t1] 
    ON [t0].[ProductID] = [t1].[ProductID]
INNER JOIN [dbo].[vw_ProductImage] AS [t2] 
    ON [t0].[ProductID] = [t2].[ProductID]
INNER JOIN [dbo].[tbl_Brand] AS [t3] 
    ON [t0].[BrandID] = [t3].[BrandID]
INNER JOIN [dbo].[tbl_ProductVariation] AS [t4] 
    ON [t0].[ProductID] = [t4].[ProductID]
LEFT OUTER JOIN [dbo].[tbl_Variation] AS [t5] 
    ON [t5].[VariationID] = [t4].[VariationID]
LEFT OUTER  JOIN [dbo].[tbl_Variation] AS [t6] 
    ON  [t6].[VariationID] = [t4].[VariationID] 
INNER JOIN [dbo].[tbl_Category] AS [t7] 
    ON [t1].[CategoryID] = [t7].[CategoryID]
WHERE ([t5].[VariationTypeID] IN(2))
AND ([t6].[VariationTypeID] IN(1))

Answer 1

如果“失败”意味着您的“左外连接”似乎不起作用，您可以尝试此查询。

SELECT [t4].[ProductVariationID],
       [t5].[UKTitle] AS [Size],
       [t6].[UKTitle] AS [Colour],
       [t0].[Title]
FROM   [dbo].[tbl_Product] AS [t0]
       INNER JOIN [dbo].[tbl_ProductVariation] AS [t4]
         ON [t0].[ProductID] = [t4].[ProductID]
       LEFT OUTER JOIN [dbo].[tbl_Variation] AS [t5]
         ON [t5].[VariationID] = [t4].[VariationID] AND
            [t5].VariationTypeID IN(2)
       LEFT OUTER JOIN [dbo].[tbl_Variation] AS [t6]
         ON [t6].[VariationID] = [t4].[VariationID] AND
            [t6].[VariationTypeID] IN(1)

我将对 VariationTypeID 的检查移至 join 子句。将它们放在 where 子句中会使外连接的行为类似于内连接。