Help identifying forum spammers via a SQL query?

Question

I would like to have a simple query that I can run against a database to return abnoralities in the time threshold that users post to our forum. If I have the following database structure:

ThreadId | UserId | PostAuthor | PostDate |
1          1000     Spammer      2010-11-14 02:52:50.093
2          1000     Spammer      2010-11-14 02:53:06.893
3          1000     Spammer      2010-11-14 02:53:22.130
4          1000     Spammer      2010-11-14 02:53:37.073
5          2000     RealUser     2010-11-14 02:53:52.383
6          1000     Spammer      2010-11-14 02:54:07.430 

I would like to set a threshold to say for instance, that if 3 posts, from the same user, fall within a time period of 1 minute, the poster may be spamming the forums. In turn, I would like to return user 'Spammer' in a query, with the number of posts made within the allotted time.

In the above example, Spammer posted 4 messages within a time period of 1 minute, so the result of the query may look like the following:

UserId | PostAuthor | PostCount | DateStart               | DateEnd
1000     Spammer      4           2010-11-14 02:52:50.093   2010-11-14 02:53:37.073

Any suggestions in the format of the returned data our welcome. The format doesn't matter me as much as correctly identifying forum abusers accurately.

Answer 1

Doesn't have everything you wanted in the output, but it's a start:

(Reword: give me all posts for which 2 or more other posts exist after it, but within one minute)

Select 
  Spammer = PostAuthor,
  NumberOfPosts = (Select Count(*) 
                   From Posts As AllPosts 
                   Where AllPosts.UserID = Posts.UserID)
From Posts
Where 2 <= (Select Count(*)
            From Posts As OtherPosts
            Where OtherPosts.UserID = Posts.UserID
              And OtherPosts.PostDate > Posts.PostDate
              And OtherPosts.PostDate < DateAdd(Minute, 1, Posts.PostDate))

Answer 2

Self join solution:

Select T1.UserId, T1.PostAuthor, T1.PostDate, Max(T2.PostDate), Count(*)
from
  Posts T1 INNER JOIN Posts T2 
  ON T1.UserId = T2.UserId and 
     T2.PostDate between T1.PostDate and dateadd(minute, 1, T1.PostDate)
group by T1.UserId, T1.PostAuthor, T1.PostDate
having count(*) >= 3