Database Structure for College system.

I am sick of not being able to see my upto date grades on the current college system as the teacher puts all of the grades in his personal Excel file, then he updates the website when he remembers.

I want to setup a small website that will allow him to login and change the grades using AJAX. Then the students will also be able to view their grades with no editing privileges, although they may add comments if I can be bothered to implant that as I need to do my work really.

The problem I am having is structureing the database and linking grades to users and then calculating the overall grade.

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Table:
http://i58.photobucket.com/albums/g268/martynball/grades.jpg

Okay, above is the table which displays the grades and such. In the database I need:

- Users
- Admin
- Edit
- Create new Units
- BlahBlah
- Student
- Add comments
- View grades
- Grades
- Unit
- Pass[num]/Merit[num]/Distinction[num]
- Marks
-


What I can't figure out is how I am going to link it all together and get the value of y/n in the correct space ect.. Ehh, if you got any ideas and have the slightest clue what I am onabout please help me Lol. I wont blame you for not understanding Lol.

Okay, if I was to make the grades table like so:

columns: GID (grade id) | unit_grade | pass | date_mod | user_id
row1:----------1------|------3.P2--|--y---|01.12.2010|---2
row2:----------2------|------3.P4--|--n---|01.12.2010|---2

How would I go about displaying this in a table with PHP? As there would be many Units and Criterias...

Info:
unit_grade - 3.P2 stands for Unit 3, P2 (Pass criteria 2)