为什么Linq to Entities会生成左外连接？

Question

我想知道是否有人知道为什么linq实体似乎总是产生左外连接。我可以在可选的关系上理解它，但是当关系是强制性的时候它没有意义。

有没有人有任何想法如何使它生成内部连接？

Answer 1

http://blogs.microsoft.co.il/blogs/idof/archive/2008/10/01/entity-framework-generated-queries-look-out.aspx

Answer 2

您可以创建内部连接。您只需使用join关键字。例如，下面是针对AdventureWorks数据库的查询：

var query = from od in db.SalesOrderHeader 
      join c in db.Customer on od.Customer.CustomerID equals c.CustomerID 
      select new { c.AccountNumber, od.OrderDate }; 

等效SQL：

Select C.AccountNumber, OD.OrderDate 
From Sales.SalesOrderHeader As OD 
    Join Sales.Customer As C 
     On C.CustomerID = OD.CustomerID 

这里就是LINQ查询生成的SQL：

SELECT 
1 AS [C1], 
[Extent2].[AccountNumber] AS [AccountNumber], 
[Extent1].[SalesOrderID] AS [SalesOrderID], 
[Extent1].[RevisionNumber] AS [RevisionNumber], 
[Extent1].[OrderDate] AS [OrderDate], 
[Extent1].[DueDate] AS [DueDate], 
[Extent1].[ShipDate] AS [ShipDate], 
[Extent1].[Status] AS [Status], 
[Extent1].[OnlineOrderFlag] AS [OnlineOrderFlag], 
[Extent1].[SalesOrderNumber] AS [SalesOrderNumber], 
[Extent1].[PurchaseOrderNumber] AS [PurchaseOrderNumber], 
[Extent1].[AccountNumber] AS [AccountNumber1], 
[Extent1].[CreditCardApprovalCode] AS [CreditCardApprovalCode], 
[Extent1].[SubTotal] AS [SubTotal], 
[Extent1].[TaxAmt] AS [TaxAmt], 
[Extent1].[Freight] AS [Freight], 
[Extent1].[TotalDue] AS [TotalDue], 
[Extent1].[Comment] AS [Comment], 
[Extent1].[rowguid] AS [rowguid], 
[Extent1].[ModifiedDate] AS [ModifiedDate], 
[Extent1].[BillToAddressID] AS [BillToAddressID], 
[Extent1].[ContactID] AS [ContactID], 
[Extent1].[ShipMethodID] AS [ShipMethodID], 
[Extent1].[CreditCardID] AS [CreditCardID], 
[Extent1].[CurrencyRateID] AS [CurrencyRateID], 
[Extent1].[CustomerID] AS [CustomerID], 
[Extent1].[SalesPersonID] AS [SalesPersonID], 
[Extent1].[TerritoryID] AS [TerritoryID] 
FROM [Sales].[SalesOrderHeader] AS [Extent1] 
INNER JOIN [Sales].[Customer] AS [Extent2] ON ([Extent1].[CustomerID] = [Extent2].[CustomerID]) OR (([Extent1].[CustomerID] IS NULL) AND ([Extent2].[CustomerID] IS NULL))