select top 20 articleId,
articleText,
(select count(*)
from comment
where articleId = a.articleId ) as NumberOfComments
from article as a
order by 3 desc
select a.articleId,
a.articleText,
count(c.articleID) as NumberOfComments
from article as a left outer join comment as c
on a.articleID = c.articleId
group by a.articleId, a.articleText
order by NumberOfComments desc
limit 20