> If there is already a correlation with the same name then append a number.

And then applies it for this query:

  SELECT first_name AS fn
    FROM staff AS s1
    JOIN students AS s2
      ON s2.mentor_id = s1.staff_num;

I think that's terrible. s1 and s2 sound to me like they're instances of the same table that you had to JOIN with itself for some reason.