Restricting capabilities of admin role in database schema Suppose I have to design database for learning management system. Which will going to have user having roles such as admin, teacher, tutor, student etc. In a system student can submit solution for an assignment in a course and teacher or tutor can provide the grade for it. 

Now while implementing is it good idea to not allow admin of a database to not to change the grade of students for an assignment? I got this suggestion that as admin is superuser (user with all capabilities) he should be able to change the grade. So what should I do?  and why?
Generally, you cannot prevent administrators from making any change they want to the database.  Many administrator actions require privileges that give them a lot of control over the database.  For instance, if they can restore from backups (something that administrators often need to do), they can overwrite everything in the database.

Designing systems that will remain secure even when the system administrator is not trusted is very challenging, and for a learning management system, is probably more expensive than is worth it.

Therefore, there's probably no point in trying to restrict admin.  Don't forbid what you can't prevent.