Database: pets_1
Question: Find the age of students who have a dog but do not have a cat as a pet.
SQL: select t1.age from student as t1 join has_pet as t2 on t1.stuid  =  t2.stuid join pets as t3 on t3.petid  =  t2.petid where t3.pettype  =  "dog" and t1.stuid not in (select t1.stuid from student as t1 join has_pet as t2 on t1.stuid  =  t2.stuid join pets as t3 on t3.petid  =  t2.petid where t3.pettype  =  "cat")