Използвайте това за един конкретен ID
select id, city_name from(
select id, city_1 as city_name from yourTable
union all
select id, city_2 from yourTable
union all
select id, city_3 from yourTable
union all
select id, city_4 from yourTable
) as t where id= yourID
http://sqlfiddle.com/#!9/7ee1f/1
Използвайте това за цялата таблица
select id, city_name from(
select id, city_1 as city_name from yourTable
union all
select id, city_2 from yourTable
union all
select id, city_3 from yourTable
union all
select id, city_4 from yourTable
) as t
order by id