In a relation R, if X is some set of attributes and Y is some prime attribute such that X uniquely determines Y is a non-trivial FD. Then is it true that R has at least two candidate keys?
For instance, take the relation schema R(Class_Id, Course_Number, Instructor_Name, Text). {Class_Id, Course_number} is a candidate key. This makes Course_Number a prime attribute.
The following functional dependency holds on R:
- {Instructor_Name, Text} uniquely determines {Course_Number}
How to determine if another candidate key exist or not?
EDIT: A Relational table
Class_Id | Course_Number | Instructor_Name | Text
2 b Jodi E
3 c Jack N
2 c Jack N
4 b Peny E
5 e Jodi N