From: Tom Lane [mailto:tgl@sss.pgh.pa.us]
>
> "Marc Sherman" <msherman@projectile.ca> writes:
> > I'd like to select the newest (max(timestamp)) row for each id,
> > before a given cutoff date; is this possible?
>
> select * from log order by timestamp desc limit 1;
Heh. I obviously simplified my situation too much.
This is closer to what I've really got:
create table user (userid int4 primary key, groupid int4);
create table log (userid int4, timestamp datetime, value int4);
I need to select sum(value) for each group, where the values chosen
are the newest log entry for each group member that is before a cutoff
date (April 1, 2001).
Here's what I'm currently using:
select user.groupid, sum(l1.value)from log as l1, userwhere user.userid=log.useridand log.timestamp in ( select
max(timestamp)from log where log.timestamp<'2001-04-01' and log.userid=l1.userid)group by user.groupid;
When I first posted, this was _very_ slow. I've since improved
it by adding an index on log(userid,timestamp) - now it's just
slow. If anyone knows how to make it faster, I'd appreciate it.
- Marc