what are the country names which has both roller coasters with speed higher than 60 and roller coasters with speed lower than 55?
select t1.name from country as t1 join roller_coaster as t2 on t1.country_id = t2.country_id where t2.speed > 60 intersect select t1.name from country as t1 join roller_coaster as t2 on t1.country_id = t2.country_id where t2.speed < 55
Yes!
select t1.country_id from country as t1 join roller_coaster as t2 on t1.country_id = t2.country_id where t2.speed > 60 intersect select t1.country_id from country as t1 join roller_coaster as t2 on t1.country_id = t2.country_id where t2.speed < 55