When I did the quiz (5/5), I assumed based on the query and the information given that the index was being helpful in the first example, so I assumed it was ind

When I did the quiz (5/5), I assumed based on the query and the information given that the index was being helpful in the first example, so I assumed it was index scanning. In that case it does have to recheck the additional condition which would definitely be slower. However, following your assumption, I would say, both would be about the same speed because it still has to sequence scan the whole table (because more b=1 rows could exist) Anyways. Seeing that the result could be either of the two answers, I agree that the question is under-specified