How many cities are there that were once host cities?
select count(distinct t1.city) from city as t1 join hosting_city as t2 on t1.city_id = t2.host_city
How many cities are there whose temperature in Feb is higher than that in Jun?
select count(*) from city as t1 join temperature as t2 on t1.city_id = t2.city_id where t2.feb > t2.jun
Please list the city names of the above results.
select t1.city from city as t1 join temperature as t2 on t1.city_id = t2.city_id where t2.feb > t2.jun union select t3.city from city as t3 join hosting_city as t4 on t3.city_id = t4.host_city