database design issue
Get 4 pieces of paper.

On the first piece, create 2 columns across the page, StudentID, StudentName and write down 1,2,3 for the StudentIDs under the StudentID column and make up some cool names like 'Dr Cheat' under the StudentName column.

On the second piece of paper, create 3 columns called StudentID, ClassID, Score and enter 1,2,3 for the StudentID and 1,1,1 for the ClassID then make up some scores - like 100%, 99%, 0%.

On the 3rd piece of paper create 2 columns - ClassID, ClassName and enter the values 1, 'How To Win by Cheating'

Now, to understand relational databases, all you need to do is on the 4th piece of paper enter the columns StudentID, StudentName, ClassID, ClassName, Score and then populate the values from the other 3 pieces of paper.

You can see you have 3 students, and some scores, and some class names for those scores - the exercise of joining them together into that 4th piece of paper is similar to writing a SQL query.

Whenever you find yourself holding 2 pieces of paper together and looking back and forward between the 2 pieces to find matching values - the column you are matching on is your JOIN column. 

That's relational database design.