How foreign key can have null values where as primary key can't have?

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I am surprise of that foreign key can refer to null value on its reference table in sql server.I would appreciate if someone explain this to me with simple example.
Thank you

Posted 2-Jul-13 8:21am

rameshKumar1717

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OriginalGriff · Answer 1 · 2013-07-02T08:31:00

Solution 1

Why shouldn't they have null values? Primary keys can't because null is not a unique value - which is a requirement of a Primary key[^]. A Foreign key[^] just relates a row in one table to a unique row in another table, and so can be null when no such row exists.

Posted 2-Jul-13 8:31am

OriginalGriff