What are the names of the storms that have affected regions in record?
select name from storm where storm_id in (select storm_id from affected_region);
How many such storms are there in the result?
select count(name) from storm where storm_id in (select storm_id from affected_region);
How about the names of storms which don't have affected region in record.
select name from storm where storm_id not in (select storm_id from affected_region);