Can't figure this out...

[eluser]GSV Sleeper Service[/eluser]
you'll have to join the two tables. something like this should work (no promises, this is off the top of my head, plus it's friday night, I'm stoned :/)

Code:

select a.*,count(c.id) as num_comments
from article a
left join article_comments c on a.id = c.articleid
group by a.id
order by num_comments

that group by is probably wrong, try it out and see how you get on.