Question

I have two tables that I am outer joining together: “Post” left outer join with “Comments”.

There is a one-to-many relationship between Post and Comments.

I would like to be able to pull the first, say 10, Post records and all of the associated Comments (if any) for each Post.

The way I would usually do this would be to have a Common Table Expression and use ROW_NUMBER() OVER. However, ROW_NUMBER() counts each row, which in this case would not work since I only want to count the Post records.

I was looking at ROW_NUMBER() OVER (PARTITION), but it does not work how I would expect it.

So if want the first 5 Posts, I would get something like:

PostNumber     PostId     CommentId
1              1          1
1              1          2
2              2          -
3              8          3
3              8          4
4              9          5
5              15         -

Answer 1

Have a look at using DENSE_RANK function

Returns the rank of rows within the
partition of a result set, without any
gaps in the ranking. The rank of a row
is one plus the number of distinct
ranks that come before the row in
question.

Something like

;WITH Vals AS (
        SELECT  p.*,
                DENSE_RANK() OVER(ORDER BY p.PostID) DenseRankID
        FROM    Post p LEFT JOIN
                Comments c ON p.PostID = c.PostID
)
SELECT  *
FROM    Vals 
WHERE   DenseRankID <= 10