Postgres 12

By using db<>fiddle, you agree to license everything you submit by Creative Commons CC0.
CREATE TABLE Restaurants (restaurant_ID INTEGER, name VARCHAR(10));
INSERT INTO Restaurants (restaurant_ID, name) VALUES
  ('1', 'Macdonalds'), ('2', 'Hubert'), ('3', 'Dorsia'), ('4', 'Another');

CREATE TABLE Identifier (restaurant_ID INTEGER, food_ID INTEGER);
INSERT INTO Identifier (restaurant_ID, food_ID) VALUES
  ('1', '1'), ('1', '4'),
  ('2', '1'), ('2', '7'), ('2', '8'),
  ('3', '1'), ('3', '4'),
  ('4', '1'), ('4', '7'), ('4', '8');

CREATE TABLE Food (food_ID INTEGER, food_name VARCHAR(7));
INSERT INTO Food (food_ID, food_name) VALUES
  ('1', 'Chips'), ('2', 'Burgers'), ('3', 'Salmon');
4 rows affected

10 rows affected

3 rows affected

with cte as (
  select restaurant_ID,
         string_agg(food_ID::varchar(10),',' order by food_ID) foods
  from identifier
  group by restaurant_ID
)
select r.* 
from Restaurants r inner join cte c
on c.restaurant_ID = r.restaurant_ID
where exists (select 1 from cte where restaurant_ID <> c.restaurant_ID and foods = c.foods)


restaurant_id
name


1
Macdonalds

2
Hubert

3
Dorsia

4
Another


with cte as (
  select restaurant_ID,
         string_agg(food_ID::varchar(10),',' order by food_ID) foods
  from identifier
  group by restaurant_ID
)
select string_agg(r.name, ',') restaurants
from Restaurants r inner join cte c
on c.restaurant_ID = r.restaurant_ID
group by foods
having count(*) > 1


restaurants


Macdonalds,Dorsia

Hubert,Another