query: select avg(age) from student where stuid not in (select stuid from has_pet)
question: What-all for all students who do not own any pets is a average age?
query_toks: select avg ( age ) from student where stuid not in ( select stuid from has_pet )
query_toks_no_value: select avg ( age ) from student where stuid not in ( select stuid from has_pet )
question_toks: What-all for all students who do not own any pets is a average age?