Question

我有BaseProducts，Images和ProductsImages（多对多）表。我有这个问题，

SELECT BaseProducts.*, 
       (SELECT TOP 1 Images.[Path] 
        FROM   Images AS Images 
               INNER JOIN ProductsImages AS ProductsImages 
                       ON Images.Id = ProductsImages.ImageId 
        WHERE  ProductsImages.BaseProductId = BaseProducts.Id 
        ORDER  BY [ProductsImages].[Order]) AS ImagePath 
FROM   CTEPage AS BaseProducts

这样可行，但对我来说看起来很笨拙。我可以将其转换为JOIN吗？

Answer 1

您可以将其转换为join。但那会更加丑陋。在SQL Server中，使用apply表达它更容易：

SELECT BaseProducts.*
       i.ImagePath, AS ImagePath
FROM CTEPage BaseProducts OUTER APPLY
     (SELECT TOP 1 Images.[Path] as ImagePath
      FROM Images i INNER JOIN
           ProductsImages pi
           ON i.Id = pi.ImageId
      WHERE pi.BaseProductId = BaseProducts.Id
      ORDER BY [ProductsImages].[Order]
     ) i;

以join执行此操作需要使用row_number()来提取“第一个”图像路径。

将子查询转换为LEFT Join？

1 个答案: