In ActiveRecord, there's a method called find_by_sql. You can't call it directly; it's a class method on an ActiveRecord model. So you have to choose which of your ActiveRecord models should be used to instantiate the rows of your result set. (What if your result set doesn't really match any of your models? Pick one arbitrarily.) Your SQL has some extra columns. What happens to the data in those columns? They get monkey-patched onto the individual objects. (Which is stupidly expensive in Ruby.) Other than that, the individual objects are fine. They even have all your smart instance methods, which may or may not behave properly with all the ad-hoc monkey patching.
If you tried to short-circuit all of that nonsense, you tend to get arrays of hash tables. Which is, in my opinion, already a perfectly adequate interface!