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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.
View ArticlePrimary 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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