Database: cre_Drama_Workshop_Groups
Question: Show all cities where at least one customer lives in but no performer lives in.
SQL: select t1.city_town from addresses as t1 join customers as t2 on t1.address_id  =  t2.address_id except select t1.city_town from addresses as t1 join performers as t2 on t1.address_id  =  t2.address_id