Question

我尝试创建类似于此的查询：

select randomId 
from myView
where ...
group by randomId

注意：EF不支持 distinct ，所以我想通过来解决组的缺乏（或者我认为）< / p>

randomId是数字

实体框架V.6.0.2

这给了我预期的结果＆lt; 1秒查询

当试图用EF做同样的事情时，我遇到了一些问题。

如果我执行与此类似的LINQ：

context.myView .Where(...) .GroupBy(mt => mt.randomId) .Select({ Id = group.Key, Count = group.Count() } )

我会得到一些相同的结果，但强制计数并进行查询＆gt; 6秒

SQL EF生成的内容如下：

SELECT 1 AS [C1], [GroupBy1].[K1] AS [randomId], [GroupBy1].[A1] AS [C2] FROM ( SELECT [Extent1].[randomId] AS [K1], COUNT(1) AS [A1] FROM [dbo].[myView] AS [Extent1] WHERE (...) GROUP BY [Extent1].[randomId] ) AS [GroupBy1]

但是，如果查询已将该计数注释掉，那么它将返回＆lt; 1秒

如果我将Select更改为：

.Select({ Id = group.Key} )

我将获取SQL查询中没有 group by 语句的所有行，并且没有 Distinct ：

SELECT [Extent1].[anotherField] AS [anotherField], -- 'this field got included automatically on this query and I dont know why, it doesnt affect outcome when removed in SQL server' [Extent1].[randomId] AS [randomId] FROM [dbo].[myView] AS [Extent1] WHERE (...)

其他尝试失败：

query.GroupBy(x => x.randomId).Select(group => group.FirstOrDefault());

生成的查询如下：

SELECT [Limit1].ALL FIELDS,... FROM (SELECT [Extent1].[randomId] AS [randomId] FROM [dbo].[myView] AS [Extent1] WHERE (...) AS [Project1] OUTER APPLY (SELECT TOP (1) [Extent2].ALL FIELDS,... FROM [dbo].[myView] AS [Extent2] WHERE (...) AS [Limit1] -- same as the where above

此查询执行得相当糟糕，仍设法返回where子句的所有ID。

有没有人知道如何强制使用组而没有像计数一样的聚合函数？

在SQL中它可以工作但是我再次拥有distinct关键字......

干杯， Ĵ

Answer 1

var query = from p in TableName 
        select new {Id = p.ColumnNameId};
var distinctItems = query.Distinct().ToList();

这是linq查询，但是你也应该能够从EF dbset编写一个等价物。如果您有问题，请告诉我。

干杯！

EntityFramework Group不包含在SQL语句中

1 个答案: