Posted by Hugo Kornelis on 11/03/05 23:39

On 3 Nov 2005 08:41:10 -0800, pb648174 wrote:

>In the below structure, if I wanted to get the Id of the comment for
>each Generic record having the latest comment time, how would I do that
>not using a subquery?
>
>Table: Generic
>Id
>Description
>
>Table: Comment
>Id
>GenericId
>CommentTime
>
>Currently I have something like the following:
>
>Select
> Generic.Id, Max(Comment.CommentTime) /*,Comment.Id for max comment
>time comment record*/
>From
> Generic
> INNER JOIN Comment ON Generic.Id = Comment.GenericId
>Group By
> Generic.Id
>
>To get it, I could do a sub query, using the above query as its source
>and joining on the max comment time, but I was wondering if there was a
>way to do it without a sub query. Keep in mind that I am looking for a
>set of Generic records and not looking for only a single record (so
>select top top 1 with order by won't work)

Hi pb648174,

You can do this in two ways.

1. Using a correlated subquery (probably the solution you already had in
mind, since you write: "if there was a way to do it without a sub
query", but I'll give it anyway)

SELECT g.Id, c.CommentTime, c.Id
FROM Generic AS g
INNER JOIN Comment AS c
ON c.GenericId = g.Id
WHERE c.CommentTime = (SELECT MAX(c2.CommentTime)
FROM Comment AS c2
WHERE c2.GenericId = c.GenericId)


2. Using a derived table. This is a subquery as well, but it's not
correlated, and it's used in the FROM clause, in place of a table or
view name:

SELECT g.Id, c.CommentTime, c.Id
FROM Generic AS g
INNER JOIN (SELECT GenericId, MAX(CommentTime) AS MaxCommentTime
FROM Comment
GROUP BY GenericId) AS c2
ON c2.GenericId = g.Id
INNER JOIN Comment AS c
ON c.GenericId = g.Id
AND c.CommentTime = c2.MaxCommentTime

(Note: both queries are untested - see www.aspfaq.com/5006 if you prefer
a tested reply)

Best, Hugo
--

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