Database: pets_1_total_0
Question: What is the first name of every student who has a dog but does not have a cat?
SQL: select t1.fname , t1.age from student_has_pet_pets as t1 where t1.pettype = 'dog' and t1.stuid not in ( select t1.stuid from student_has_pet_pets as t1 where t1.pettype = 'cat' )