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I am making a mock database and I have a student table, student_class linking table, and a class table. How can I make it so that a student cannot be registered for the same class twice?
Example: StudentID 21 and classID 34 can be entered X number of times in the linking table.
The tables are designed 3NF, too.
In your student_class linking table (otherwise called a composite table), make both values, StudentID and ClassID, primary keys. So that table will have 2 columns that are composite primary keys and also foreign keys to their associated tables. Does that make sense?