# search for keys in a given building, 
# issued to persons with a given status
IssuedKey->set_sql(building_id_person_status =>
  'SELECT id FROM IssuedKey, Person
   WHERE Person.person_id=IssuedKey.person_id
   AND IssuedKey.building_id=? AND Person.status=?');

my (@keys) = IssuedKey->search_building_id_person_status(
  $building, $status);