Yeah, it's definitely more expressive and terse I just don't think your argument against WHERE/HAVING is incredibly strong. Someone could also just do subqueries and only use WHERE and achieve the exact same behavior that you offer (albeit with a ton more typing).

HAVING exists because it was created prior to subqueries/dynamic tables, otherwise we'd have been likely to just use:

    select * from (select category, sum(num_comments) as comments from posts group by category) as temp where comments > 7