C# 使用多个from子句语法与传统连接语法的linq到sql连接

使用2

from

子句和

where

这样的子句编写联接有什么区别：

var SomeQuery = from a in MyDC.Table1
                from b in MyDC.Table2
                where a.SomeCol1 == SomeParameter && a.SomeCol2 === b.SomeCol1

以及使用join操作符编写一个

连接

这适用于两个表上的
join
，但当然，有时我们需要连接更多的表，如果我们选择上述语法，我们需要将其他
from
子句与
where
组合

我知道两个语法查询都返回相同的数据，但我想知道是否存在性能差异，或者其他类型的差异，这最终会使一种语法优于另一种语法

谢谢你的建议。
这两个问题实际上回答得很好



我已经包括了两个关于如何将三个不同的LINQ表达式转换为SQL的示例

隐式联接：

from prod in Articles
from kat in MainGroups
where kat.MainGroupNo == prod.MainGroupNo
select new { kat.Name, prod.ArticleNo }

from prod in Articles
join kat in MainGroups on prod.MainGroupNo equals kat.MainGroupNo
select new { kat.Name, prod.ArticleNo }

from prod in Articles
join g1 in MainGroups on prod.MainGroupNo equals g1.MainGroupNo into prodGroup
from kat in prodGroup.DefaultIfEmpty()
select new { kat.Name, prod.ArticleNo }

将被翻译成

SELECT [t1].[Name], [t0].[ArticleNo]
FROM [dbo].[Article] AS [t0], [dbo].[MainGroup] AS [t1]
WHERE [t1].[MainGroupNo] = [t0].[MainGroupNo]

SELECT [t1].[Name], [t0].[ArticleNo]
FROM [dbo].[Article] AS [t0]
INNER JOIN [dbo].[MainGroup] AS [t1] ON [t0].[MainGroupNo] = [t1].[MainGroupNo]

SELECT [t1].[Name] AS [Name], [t0].[ArticleNo]
FROM [dbo].[Article] AS [t0]
LEFT OUTER JOIN [dbo].[MainGroup] AS [t1] ON [t0].[MainGroupNo] = [t1].[MainGroupNo]

内部联接：

from prod in Articles
from kat in MainGroups
where kat.MainGroupNo == prod.MainGroupNo
select new { kat.Name, prod.ArticleNo }

from prod in Articles
join kat in MainGroups on prod.MainGroupNo equals kat.MainGroupNo
select new { kat.Name, prod.ArticleNo }

from prod in Articles
join g1 in MainGroups on prod.MainGroupNo equals g1.MainGroupNo into prodGroup
from kat in prodGroup.DefaultIfEmpty()
select new { kat.Name, prod.ArticleNo }

将被翻译成

SELECT [t1].[Name], [t0].[ArticleNo]
FROM [dbo].[Article] AS [t0], [dbo].[MainGroup] AS [t1]
WHERE [t1].[MainGroupNo] = [t0].[MainGroupNo]

SELECT [t1].[Name], [t0].[ArticleNo]
FROM [dbo].[Article] AS [t0]
INNER JOIN [dbo].[MainGroup] AS [t1] ON [t0].[MainGroupNo] = [t1].[MainGroupNo]

SELECT [t1].[Name] AS [Name], [t0].[ArticleNo]
FROM [dbo].[Article] AS [t0]
LEFT OUTER JOIN [dbo].[MainGroup] AS [t1] ON [t0].[MainGroupNo] = [t1].[MainGroupNo]

左外连接：

from prod in Articles
from kat in MainGroups
where kat.MainGroupNo == prod.MainGroupNo
select new { kat.Name, prod.ArticleNo }

from prod in Articles
join kat in MainGroups on prod.MainGroupNo equals kat.MainGroupNo
select new { kat.Name, prod.ArticleNo }

from prod in Articles
join g1 in MainGroups on prod.MainGroupNo equals g1.MainGroupNo into prodGroup
from kat in prodGroup.DefaultIfEmpty()
select new { kat.Name, prod.ArticleNo }

将被翻译成

SELECT [t1].[Name], [t0].[ArticleNo]
FROM [dbo].[Article] AS [t0], [dbo].[MainGroup] AS [t1]
WHERE [t1].[MainGroupNo] = [t0].[MainGroupNo]

SELECT [t1].[Name], [t0].[ArticleNo]
FROM [dbo].[Article] AS [t0]
INNER JOIN [dbo].[MainGroup] AS [t1] ON [t0].[MainGroupNo] = [t1].[MainGroupNo]

SELECT [t1].[Name] AS [Name], [t0].[ArticleNo]
FROM [dbo].[Article] AS [t0]
LEFT OUTER JOIN [dbo].[MainGroup] AS [t1] ON [t0].[MainGroupNo] = [t1].[MainGroupNo]

如果您想测试如何将表达式转换为SQL，我建议您尝试。这是一个非常棒的工具，可以用来找出这类东西。
那么还有什么更好的呢？2个或多个from子句或2个或多个join子句？根据join子句，似乎更可取。这既不能回答问题，也不能提供任何解释。
var result = from a in DB.classA
from b in DB.classB
where a.id.Equals(b.id)
select new{a.b};