Oracle 11g Release 2

By using db<>fiddle, you agree to license everything you submit by Creative Commons CC0.
CREATE TABLE mytable(
   City  VARCHAR(8) NOT NULL
  ,Value INTEGER  NOT NULL
);

INSERT INTO mytable(City,Value) VALUES ('Helsinki',1);
1 rows affected

INSERT INTO mytable(City,Value) VALUES ('Helsinki',2);
1 rows affected

INSERT INTO mytable(City,Value) VALUES ('Helsinki',5);
1 rows affected

INSERT INTO mytable(City,Value) VALUES ('Kuopio',4);
1 rows affected

INSERT INTO mytable(City,Value) VALUES ('Kuopio',5);
1 rows affected

INSERT INTO mytable(City,Value) VALUES ('Joensuu',1);
1 rows affected

INSERT INTO mytable(City,Value) VALUES ('Joensuu',2);
1 rows affected

INSERT INTO mytable(City,Value) VALUES ('Joensuu',3);
1 rows affected

SELECT c.city, v.value
FROM 
    (SELECT DISTINCT city FROM mytable) c
    CROSS JOIN (SELECT rownum value FROM DUAL CONNECT BY level<= 5) v
    LEFT JOIN mytable t ON t.city = c.city AND t.value = v.value
WHERE t.city IS NULL
ORDER BY c.city, v.value


CITY
VALUE


Helsinki
3

Helsinki
4

Joensuu
4

Joensuu
5

Kuopio
1

Kuopio
2

Kuopio
3