我有这个LINQ声明，

var carriageways = from carriageway in dataModelCurrentEntities.Carriageway
                   where carriageway.RoadId == roadId && carriageway.DistanceBreak == false
                   orderby carriageway.CarriagewayStartInMetre
                   select new CarriagewaySummary
                   {
                       StartMetres = carriageway.CarriagewayStartInMetre, 
                       EndMetres = carriageway.CarriagewayEndInMetre
                   };

它以这种形式（对实体的LINQ）生成SQL，

SELECT 
Project1.field1 AS field1
Project1.field2 AS field2
FROM ( SELECT 
    Extent1.field1 AS field1, 
    Extent1.field2 AS field2
    FROM table AS Extent1
    WHERE blah
)  AS Project1
ORDER BY blah ASC

这是什么原因呢？我本以为这样的事情就足够了，

SELECT 
fields
FROM table as Project1
WHERE blah
ORDER BY blah ASC

我记得LINQ to SQL倾向于生成更简单的SQL。

我已经看过带有连接等的更复杂的示例，而对实体的LINQ似乎会生成更复杂的SQL。

更新：

这很有趣，因为我试图测试您在说什么，而我遇到了这个LINQ，

var attachments = (from a in entities.Attachments
                  where a.AttachmentID == 749
                  select new {a.AddedOn, a.AddedBy});

然后生成此SQL，

SELECT 
[Extent1].[AttachmentID] AS [AttachmentID], 
[Extent1].[AddedOn] AS [AddedOn], 
[Extent1].[AddedBy] AS [AddedBy]
FROM [dbo].[Attachment] AS [Extent1]
WHERE 749 = [Extent1].[AttachmentID]

这个没有子查询。

区别是（至少是其中之一）…等待它。Informix。上面生成子查询的第一个查询是使用notifyix。第二个查询不是SQL Server。

它可能不那么简单，因为查询是不同的。

我确实接受了第二个查询，并将其分解成这样的子查询（手动），

SELECT 
[Project1].[AttachmentID] AS [AttachmentID], 
[Project1].[AddedOn] AS [AddedOn], 
[Project1].[AddedBy] AS [AddedBy]

    FROM ( SELECT

    [Extent1].[AttachmentID] AS [AttachmentID], 
    [Extent1].[AddedOn] AS [AddedOn], 
    [Extent1].[AddedBy] AS [AddedBy]
    FROM [dbo].[Attachment] AS [Extent1]
    WHERE 749 = [Extent1].[AttachmentID]
    ) AS Project1

SQL Server为两者显示了相同的执行计划，因此正如您所说的，SQL Server能够很好地对其进行优化。另一方面，Informix在优化方面是可耻的。