[support] Views filter rooms by occupacy

I have a site with 2 content types: rooms and reservations. I want to list all the rooms without a reservation for an interval, and also for services, capacity, .... I tried creating a view with a PHP filter to check free rooms, but then if the page lists 10 rooms, sometimes there are 7, 2, or 0; because the filter lists the 10 rooms and after remove the occupied ones. I have tried to create a "subview" filter to select nodes "not in (view of occupied rooms); but I haven't find a way to do so. Any idea of how to accomplish this? thanks -- *Ser freak no és imprescindible per ser informàtic, però ajuda.