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Channel: Primary key which is foreign key in an relationship is specified NOT NULL. Why? - Database Administrators Stack Exchange
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Answer by TomTom for Primary key which is foreign key in an relationship is...

A foreign key null means that there may not be an entry on the other side. In a master-detail relationship it means a detail can exist without a master.

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Primary key which is foreign key in an relationship is specified NOT NULL. Why?

I have question about a foreign key. Primary key which is foreign key in an relationship is specified NOT NULL in some book's example. Why? I was thinking that primary key couldn't take on value "null"...

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