On Sep 25, 2007, at 17:30 , Alvaro Herrera wrote:
Michael Glaesemann wrote:
select dom_id,
dom_name,
usr_count
from domains
natural join (select usr_dom_id as dom_id,
count(usr_dom_id) as usr_count
from users) u
where usr_count > 0
order by dom_name;
Maybe the usr_count should be tested in a HAVING clause instead of
WHERE? And put the count(*) in the result list instead of a
subselect.
That feels more natural to me anyway.
I believe you'd have to write it like
select dom_id, dom_name, count(usr_dom_id) as usr_count
from domains
join users on (usr_dom_id = dom_id)
having count(usr_dom_id) > 0
order by dom_name;
I don't know how the performance would compare. I think the backend
is smart enough to know it doesn't need to perform two seq scans to
calculate count(usr_dom_id), but I wasn't sure.
Madison, how do the two queries compare with explain analyze?
Michael Glaesemann
grzm seespotcode net
---------------------------(end of broadcast)---------------------------
TIP 6: explain analyze is your friend
