CREATE TABLE #cities (cityId INT, city VARCHAR(100));
INSERT INTO #cities (city)
VALUES (1, 'Metropolis A'),
       (2, 'Town B'),
       (3, 'Village C');

CREATE TABLE #assignements (assignmentID INT, cityId INT, desciption VARCHAR(100));
INSERT INTO #assignements (assignmentID, cityId, desciption)
VALUES (1, 1, 'Test Alpha Metropol'),
       (1, 2, 'Test Alpha Town'),
       (1, 3, 'Test Alpha Village'),
       (2, 1, 'Test Beta Metropol');

INSERT INTO #assignements (assignmentID, cityId, desciption)
VALUES (2, 3, 'Test Beta Village');

assignmentID  city
1             'Metropolis A'
2             'Metropolis A'

assignmentID  city
1             'Metropolis A'
2             'Metropolis A'
1             'Village C'
2             'Village C'

INSERT INTO #assignements (assignmentID, cityId, desciption)
VALUES (3, 2, 'Test Gamma Town');

select a.assignmentID, c.city
from #cities c
join #assignements a on a.cityId = c.cityId
where c.cityId in (
                    select c.cityId
                    from #cities c
                    left join #assignements a on a.cityId = c.cityId
                    group by c.cityId
                    having count(*) = (select count(distinct assignmentID) from #assignements))