无法将SQL更改为主键（AI）而不是用户名

I recently started using Jpmaster77's Login Script, and it has shown to be very great. However, now I am trying to experiment with it. I am trying to create a new table at the beginning of the row named "id" that has a primary key or AI, rather than the table username. To my knowledge, only one table can have a primary key or AI, but yet when I try to create this "id" table, the script becomes unable to register on. I don't get an ACTUAL error, but I get this message after attempting to log in "I recently started using Jpmaster77's Login Scr