Find all citizens living in all requested cities at the same time

gistfile1.MD

/*

 citizens              citizenships
+------+---------+    +-------------+-----+     cities
| id   | int     |<---| citizen_id  | int |    +-------+---------+
| name | varchar |    | city_id     | int |--->| id    | int     |
+------+---------+    +-------------+-----+    | name  | varchar |
                                               +-------+---------+
*/

drop table if exists citizens, cities, citizenships;

create table citizens (
  id int not null,
  name varchar(255),
  primary key (id)
);

create table cities (
  id int not null,
  name varchar(255),
  primary key (id)
);

create table citizenships (
  citizen_id int not null,
  city_id int not null,
  primary key (citizen_id, city_id)
);

insert into citizens (id, name) values
  (1, 'Anna'),
  (2, 'Julia'),
  (3, 'Anastasia');

insert into cities (id, name) values
  (1, 'Los Angeles'),
  (2, 'Moscow'),
  (3, 'St. Petersburg'),
  (4, 'New York');

insert into citizenships (citizen_id, city_id) values
  (1, 1), (1, 2), (1, 3),
  (2, 1), (2, 2), (2, 3), (2, 4),
  (3, 1), (3, 2), (3, 4);

-- Find all citizens living in all requested cities at the same time

-- Example below:
/*
User requested: I need to see people who live in LA, MSK and SPb:

---------------------------------------------------------
Citizens  |   Cities
---------------------------------------------------------
Anna      | Los Angeles, Moscow, St. Petersburg           - RETURNED
Julia     | Los Angeles, Moscow, St. Petersburg, New York - RETURNED
Anastasia | Los Angeles, Moscow,                 New York - NOT returned
---------------------------------------------------------
*/

-- TODO: Write your query here
  
select citizens.name as "Citizens", string_agg(cities.name, ', ') as "Cities" from citizens 
  left outer join citizenships on citizens.id = citizenships.citizen_id
  left outer join cities on cities.id = citizenships.city_id
  where citizens.id in (
    select citizens_id from (
      select citizens.id as "citizens_id", string_agg(CAST(cities.id AS varchar(10)), ',') as "cities_ids" from citizens 
      left outer join citizenships on citizens.id = citizenships.citizen_id
      left outer join cities on cities.id = citizenships.city_id
      where citizenships.city_id in (1,2,3)
      group by citizens.id
    ) as citizens_ids
    where cities_ids = '1,2,3'
  ) group by citizens.name, citizen_id;