How many countries have roller coaster?
select count ( distinct t1.name ) from country as t1 join roller_coaster as t2 on t1.country_id = t2.country_id
How many countries have more than one roller coaster?
select count ( * ) from ( select t1.name from country as t1 join roller_coaster as t2 on t1.country_id = t2.country_id group by t1.name having count ( * ) > 1 )
Show the names of the countries that have more than one roller coaster.
select t1.name from country as t1 join roller_coaster as t2 on t1.country_id = t2.country_id group by t1.name having count ( * ) > 1
Show the number of roller coasters of Australia and Finland.
select t1.name,count ( * ) from country as t1 join roller_coaster as t2 on t1.country_id = t2.country_id group by t1.name having count ( * ) > 1
Show the names of roller coasters of Australia and Finland in separate table
select t2.name from country as t1 join roller_coaster as t2 on t1.country_id = t2.country_id where t1.name = 'Austria' or t1.name = 'Finland'