I believe you are right. The rank is highly dependent on the entire population. Since students are taking exams online at indefinite times, their performances vary at a non-predictable manner. To determine a specific rank, I need to take a snapshot from the entire table.

Previously, I thought of having another table that only holds information such as the rank of the student. The problem with this idea is that everytime a student improves in rank (like from 9th place moving up to 5th place), I need to update the ranks of all entries respectively.

Thanks for the comments