create sequence ratings_id_seq;
create table ratings (
  id integer not null
    default nextval('ratings_id_seq'),
  name varchar(16) not null unique
    check (length(name) > 0),
  description_text,
  primary key (id)
);

create sequence auditoriums_id_seq;
create table auditoriums (
  id integer not null
    default nextval('auditoriums_id_seq'),
  theatre_id integer not null
    references theatres(id)
  auditorium_identifier varchar(64) not null
    check (length(auditorium_identifier) >= 1),
  seats_available integer not null,
  primary key (id),
  unique(theatre_id, auditorium_identifier)
);
