For the following entity-relationship diagram, what could the primary key be in the Grade entity?
A)Primary key from Student entity
B)Primary key from Course entity
C)The student's grade in the course.
D)Primary key made up of the primary keys from Student entity and Course entity

Question

For the following entity-relationship diagram, what could the primary key be in the Grade entity? 
A)Primary key from Student entity 
B)Primary key from Course entity 
C)The student's grade in the course. 
D)Primary key made up of the primary keys from Student entity and Course entity

Quizplus · Accepted Answer

The Grade entity is a junction table between the Student and Course entities, so its primary key should be made up of the primary keys from both of these entities. This is known as a composite primary key. Using just one of the primary keys (A or B) would not uniquely identify a record in the Grade entity, and using the student's grade (C) would not allow for multiple grades for the same student and course combination.

For the Following Entity-Relationship Diagram, What Could the Primary Key