Consider the following relational schema:

People(person id, person name)

Purchases(purchase id, person id, cost)

What is the intention of following queries? Do they return the same tuples on any database instance? Explain your answer

a. SELECT person_id FROM Purchases GROUP BY person_id HAVING max ( cost ) < 100

b. SELECT person_id FROM People WHERE person_id NOT IN ( SELECT person_id FROM Purchases WHERE cost >= 100)