how to translate the SQL code "having" condition into LinqToSQL or LinqToEntites?

Question

Could you tell me how to translate the following SQL code to Linq To SQL or Linq To Entites?

The correst SQL code is:

select CollectId,url,userid,pubtime from Collect group by url,collectid,userid,pubtime having pubtime >= (select max(pubtime) from collect d where d.url = collect.url ) order by Collect.pubtime desc

The database table sript is:

if exists (select * from sysobjects where id = OBJECT_ID('[Collect]') and OBJECTPROPERTY(id, 'IsUserTable') = 1) DROP TABLE [Collect]

CREATE TABLE [Collect] ( [CollectId] [int] IDENTITY (1, 1) NOT NULL, [Url] [nvarchar] (200) NULL, [UserId] [nvarchar] (50) NULL, [PubTime] [datetime] NULL)

ALTER TABLE [Collect] WITH NOCHECK ADD CONSTRAINT [PK_Collect] PRIMARY KEY NONCLUSTERED ( [CollectId] ) SET IDENTITY_INSERT [Collect] ON

INSERT [Collect] ([CollectId],[Url],[UserId],[PubTime]) VALUES ( 1,'www.sohu.com','Mike','2008-10-10 0:00:00') INSERT [Collect] ([CollectId],[Url],[UserId],[PubTime]) VALUES ( 2,'www.echina365.com','Lily','2008-10-15 0:00:00') INSERT [Collect] ([CollectId],[Url],[UserId],[PubTime]) VALUES ( 3,'www.php.com','Tom','2008-10-20 0:00:00') INSERT [Collect] ([CollectId],[Url],[UserId],[PubTime]) VALUES ( 4,'www.echina365.com','YaoMing','2008-10-23 0:00:00') INSERT [Collect] ([CollectId],[Url],[UserId],[PubTime]) VALUES ( 5,'www.echina365.com','Mike','2008-10-25 0:00:00') INSERT [Collect] ([CollectId],[Url],[UserId],[PubTime]) VALUES ( 6,'www.sohu.com','Jack','2008-10-26 0:00:00') INSERT [Collect] ([CollectId],[Url],[UserId],[PubTime]) VALUES ( 7,'www.echina365.com','Tracy','2008-11-2 0:00:00') INSERT [Collect] ([CollectId],[Url],[UserId],[PubTime]) VALUES ( 8,'www.php.com','YaoMing','2008-11-5 0:00:00')

SET IDENTITY_INSERT [Collect] OFF

Answer 1

Since your "having" condition isn't actually on an aggregated column, couldn't you just use the "where" clause?

select distinct CollectId, url, userid, pubtime
from Collect
where pubtime >= (select max(pubtime) from collect d where d.url = collect.url)
order by Collect.pubtime desc

This gets the same result given the dataset you've supplied. The LINQ statement then becomes reasonably simple:

var rows = (from c in Collect
where c.PubTime >= (
    from d in Collect
    where d.Url == c.Url
    select d.PubTime).Max()
orderby c.PubTime descending
select c).Distinct();

I could be misinterpreting your intent though. Perhaps my version of the query doesn't do exactly what you want. If so, leave me a comment and I'll delete the answer so as not to confuse the issue.

Answer 2

Matt Hamilton, thank you. You solved the problem.