Question

I have been trying to understand a little bit about how to implement custom paging in SQL, for instance reading articles like this one.

I have the following query, which works perfectly. But I would like to implement paging with this one.

SELECT TOP x PostId FROM ( SELECT PostId, MAX (Datemade) as LastDate
 from dbForumEntry 
 group by PostId ) SubQueryAlias
 order by LastDate desc

What is it I want

I have forum posts, with related entries. I want to get the posts with the latest added entries, so I can select the recently debated posts.

Now, I want to be able to get the “top 10 to 20 recently active posts”, instead of “top 10”.

What have I tried

I have tried to implement the ROW functions as the one in the article, but really with no luck.

Any ideas how to implement it?

Answer 1

In SQL Server 2012 it is very very easy

SELECT col1, col2, ...
 FROM ...
 WHERE ... 
 ORDER BY -- this is a MUST there must be ORDER BY statement
-- the paging comes here
OFFSET     10 ROWS       -- skip 10 rows
FETCH NEXT 10 ROWS ONLY; -- take 10 rows

If we want to skip ORDER BY we can use

SELECT col1, col2, ...
  ...
 ORDER BY CURRENT_TIMESTAMP
OFFSET     10 ROWS       -- skip 10 rows
FETCH NEXT 10 ROWS ONLY; -- take 10 rows

(I’d rather mark that as a hack – but it’s used, e.g. by NHibernate. To use a wisely picked up column as ORDER BY is preferred way)

to answer the question:

--SQL SERVER 2012
SELECT PostId FROM 
        ( SELECT PostId, MAX (Datemade) as LastDate
            from dbForumEntry 
            group by PostId 
        ) SubQueryAlias
 order by LastDate desc
OFFSET 10 ROWS -- skip 10 rows
FETCH NEXT 10 ROWS ONLY; -- take 10 rows

New key words offset and fetch next (just following SQL standards) were introduced.

But I guess, that you are not using SQL Server 2012, right? In previous version it is a bit (little bit) difficult. Here is comparison and examples for all SQL server versions: here

So, this could work in SQL Server 2008:

-- SQL SERVER 2008
DECLARE @Start INT
DECLARE @End INT
SELECT @Start = 10,@End = 20;


;WITH PostCTE AS 
 ( SELECT PostId, MAX (Datemade) as LastDate
   ,ROW_NUMBER() OVER (ORDER BY PostId) AS RowNumber
   from dbForumEntry 
   group by PostId 
 )
SELECT PostId, LastDate
FROM PostCTE
WHERE RowNumber > @Start AND RowNumber <= @End
ORDER BY PostId