Question

我有一个linq语句，它应该产生一个通用的左外连接（特别是使用空值）但是它产生了一个奇怪的sql，它也使用了count（*）

这是linq：

(from ccc in cDataContext.CategoryCountryCategoryTypeMappings
 join cl in currentLogs on ccc.CategoryCountryCategoryTypeMappingID equals
 cl.CategoryCountryCategoryTypeMappingID 
 into final
 select final);

当前日志如下所示：

 (from dll in cDataContext.DownloadLogs
  where dll.DTS.Hour == DateTime.Now.Hour && dll.DTS.Date== DateTime.Now.Date
  select dll)

输出sql变为：

 SELECT [t1].[LogId], [t1].[CategoryCountryCategoryTypeMappingID], [t1].[CaptureTime], [t1].[Response], [t1].[DTS], [t1].[DLID], (
    SELECT COUNT(*)
    FROM clients.[dbo].[DownloadLog] AS [t2]
    WHERE ([t0].[CategoryCountryCategoryTypeMappingID] = [t2].[CategoryCountryCategoryTypeMappingID]) 
) AS [value]
FROM clients.[Store].[CategoryCountryCategoryTypeMappings] AS [t0]
LEFT OUTER JOIN clients.[dbo].[DownloadLog] AS [t1] ON ([t0].[CategoryCountryCategoryTypeMappingID] = [t1].[CategoryCountryCategoryTypeMappingID])
ORDER BY [t0].[CategoryCountryCategoryTypeMappingID], [t1].[LogId]

我在寻找什么：

SELECT * FROM 
clients.[Store].[CategoryCountryCategoryTypeMappings] AS [t0]
LEFT INNER JOIN clients.[dbo].[DownloadLog] AS [t1] 
ON ([t0].[CategoryCountryCategoryTypeMappingID] = [t1].[CategoryCountryCategoryTypeMappingID])

我如何生成所需的sql？

Answer 1

MSDN具有良好的linq示例。 http://msdn.microsoft.com/en-US/vstudio/ee908647.aspx

对于左外连接：

var q = 
    from c in categories 
    join p in products on c equals p.Category into ps 
    from p in ps.DefaultIfEmpty() 
    select new { Category = c, ProductName = p == null ? "(No products)" : p.ProductName };

Linq使用左外连接生成非预期的sql

1 个答案: