title: Modeling a 1 to 1..n relationship in the database
body: <p>How would you model booked hotel room to guests relationship (in PostgreSQL, if it matters)? A room can have several guests, but at least one.</p>
  
  <p>Sure, one can relate guests to bookings with a foreign key <code>booking_id</code>. But how do you enforce on the DBMS level that a room must have at least one guest?</p>
  
  <p>May be it's just impossible?</p>