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
