Обсуждение: help optimizing query

Hi all,

The situation: there are users in one table, and their access statistics
in the other. Now I want to find users whose last access time was more
than one month ago. As I've only had to write quite simple queries
involving no sub-selects so far, I'd like to ask your opinion if this
one scales at all or not.

SELECT u.login,last_use_time
FROM users u
JOIN (SELECT user_id, MAX(stop_time) AS last_use_time
       FROM stats
       GROUP BY user_id) AS s ON (u.id=s.user_id)
WHERE status='3' AND next_plan_id IS NULL
   AND last_use_time < now() - interval '1 month'
ORDER BY last_use_time;

It seems to do the job, but how good is it in the long run? Any way I
could tweak it?

Thanks.

> It seems to do the job, but how good is it in the long run? Any way I
> could tweak it?


I think this form will work the best:


SELECT u.login, MAX(s.stop_time) AS last_use_time
FROM users u, stats s
WHERE u.id=s.user_id
AND u.status='3' AND u.next_plan_id IS NULL
GROUP BY u.login
HAVING MAX(s.stop_time) < (now() - interval '1 month')
ORDER BY last_use_time;

On Feb 9, 2008 8:04 PM, Adam Rich <adam.r@sbcglobal.net> wrote:
> > It seems to do the job, but how good is it in the long run? Any way I
> > could tweak it?
>
>
> I think this form will work the best:
>
>
> SELECT u.login, MAX(s.stop_time) AS last_use_time
> FROM users u, stats s
> WHERE u.id=s.user_id
> AND u.status='3' AND u.next_plan_id IS NULL

If only ba small number of fields have next_plan as null, an they
correlate to the status normally, then an index on state where
next_plan_id is null might help here.

> GROUP BY u.login
> HAVING MAX(s.stop_time) < (now() - interval '1 month')
> ORDER BY last_use_time;