create table City (city_id integer not null primary key, city_name varchar2( 80 ) not null unique);

create table Shop (shop_id integer not null primary key, city_id integer not null, shop_name varchar2( 80 ) not null);

create table Station (station_id integer not null primary key, city_id integer not null, station_name varchar2( 80 ) not null);

alter table Station add constraint Station_ak unique (city_id, station_id);

alter table Shop add constraint Shop_ak unique (city_id, shop_id);

create table Shop_Station (city_id integer not null, shop_id integer not null, station_id integer not null);

alter table Shop_Station add constraint Shop_Station_Shop_fk
  foreign key (city_id, shop_id) references Shop (city_id, shop_id);

alter table Shop_Station add constraint Shop_Station_Station_fk 
  foreign key (city_id, station_id) references Station (city_id, station_id);