I have entities "Student" and "Course" and they are connected with relationship many-to-many called "Exam". The relationship "Exam" has an atribute "Grade". For this ER model, I have made a relational schema:
Student(StudentID, StudentName, DoB) Course(CourseID, CourseName) Exam(StudentID, CourseID, Grade)
Can someone explain how would you put in a relational schema the fact that a student can't get multiple grades for a single course? For example, we can't have records like
(Student1, Course1, Grade1) and
(Student1, Course1, Grade2).