Duplicate usernames can be created when signing up

[lsun0547]

When signing up for a new account, it is possible to make an account with a username that already exists in the table for the other type of account.
ex: If there is a student account with the username "hello" it is possible for a user to sign up for a parent account with the same username.

My suggestion is to merge the student table into the user table and add another column that tells the account type. Then the SQL queries for the student and user tables should be changed to match with the new user table.