I can assure you that it *does* work for the scenario that you describe, as long as you configure it right. We are using the external database enrolment in our university (for the last 6 years) and students have several records in the external enrolment table (as many as courses they are supposed to be taking
On the other hand, even if the table can't be changed, you can always create a new read-only view with the data in the format you need (in fact, that's what we did for several years, creating a view from several tables in our SIS database).
Por cierto, a juzgar por tu nombre diría que hablas español (y casi seguro que catalán también
Saludos.
Iñaki.