Question

我正在使用LINQ从数据库中获取记录，我在SQL服务器上编写了一个SQL查询，我在asp .net MVC中编写LINQ查询，我使用group by left join并count in查询所以它说它在select中没有范围变量，我尝试了很多但是失败了，以下是查询

SQL查询：

select Post_ID, Post, com.cmtcount  from Posts left join (select Comments.postID,
 Count(Comments.comments) as cmtcount from Comments group by postID)
 as com on com.postID = Post_ID;

Linq查询：

from row in db.Posts join cmtrow in db.Comments on row.Post_ID
 equals cmtrow.postID into ps from cmtrow in ps.DefaultIfEmpty()
  group cmtrow by cmtrow.Comments_ID into grouped  select new 
{ row.Post1, row.Posted_by,cmtrow.comments,
 count = grouped.Count(t=>t.Comments_ID!=null) };

Answer 1

我会像这样编写SQL查询：

SELECT
      p.Post_ID
    , p.Post
    , COUNT(c.CommentID) as cmtcount
FROM Posts p
    LEFT JOIN Comments c ON c.PostID = p.Post_ID
GROUP BY p.Post_ID, p.Post

在LinQ中，你可以这样写：

from p in db.Posts
join c in db.Comments on p.Post_ID equals c.PostID into commentsInPost
select new
{
    PostId = p.Post_ID,
    Post = p.Post1,
    cmtcount = commentsInPost.Count()
};

LinQ生成的SQL如下：

SELECT 
    [Extent1].[Post_ID] AS [Post_ID], 
    [Extent1].[Post] AS [Post], 
    (SELECT 
        COUNT(1) AS [A1]
        FROM [dbo].[Comments] AS [Extent2]
        WHERE [Extent1].[Post_ID] = [Extent2].[PostID]) AS [C1]
FROM [dbo].[Posts] AS [Extent1]

两种SQL语法都是正确的，并且会返回相同的结果，由您决定使用哪一种。

使用group by left join并使用linq进行计数

1 个答案: