Re: Get most recent message between users?

Thank you and sorry for the vagueness. The answer I was looking for
was Steves last suggestion - getting the newest messages between all
users which would return...

6 | 1 | 2 | 2009-07-10
5 | 2 | 3 | 2009-06-10
3 | 1 | 4 | 2009-07-21
2 | 1 | 3 | 2009-06-21

On Aug 17, 6:03 pm, scrawf(dot)(dot)(dot)(at)pinpointresearch(dot)com (Steve Crawford)
wrote:
> Nick wrote:
> > messages (id, to_user, from_user, created)
> > 1 | 1 | 2 | 2009-05-21
> > 2 | 1 | 3 | 2009-06-21
> > 3 | 1 | 4 | 2009-07-21
> > 4 | 2 | 1 | 2009-05-10
> > 5 | 2 | 3 | 2009-06-10
> > 6 | 1 | 2 | 2009-07-10
>
> > How could I get the most recent message between two users?
>
> Depends on what you want (all untested).
>
> If you want the most recent message from user 1 to user 2 then:
> SELECT ... where from_user=1 and to_user=2 order by created desc limit 1;
>
> If you want the most recent message _between_ two users (either
> direction), then you need to include both directions in the where clause:
> where (from_user=1 and to_user=2) or (from_user=2 and to_user=1)...
>
> If you want the most recent message time for all messages for all
> user-pairs (one direction)
> ...to_user, from_user, max(created)...group by to_user,from_user
>
> Or most-recent between all user-pairs:
> ...int4smaller(from_user,to_user), int4larger(from_user,to_user),
> max(created) group by int4smaller(from_user,to_user),
> int4larger(from_user,to_user)
>
> Optimizing some of these could be "fun", though.
>
> Cheers,
> Steve
>
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