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Primary key x Foreign key

Primary key x Foreign key

Super Learner

Hi, all!
My question basically is: a foreign key in a child table is necessarily a primary key in the parent table? Would it make a difference if this is a mandatory criteria or not?
Thank you!

1 Answer

This is a good question and let me try to answer this .
a) Does the FK on child table always a PK on the parent table ?
No, it does not have to be necessarily . If that is true , then the model is one to many relationship for sure

But let us consider this model (Person—————-> Courses )
In this case, many people can enroll in a course ID and a course ID refers to many people

However, in real world, these types of relationships become very inefficient and usually these are broken down into at least two one- many relationship

But FK in child table should not be a pK necessarily in parent table . In most of the case, it is true by design

Thank you. So, although this is not a formal requirement, by means of practice, in most of the cases it is, right?

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