Information AboutForeign Key |
| CATEGORIES ABOUT FOREIGN KEY | |
| data modeling | |
| databases | |
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Foreign keys that refer back to the same table are called recursive foreign keys. For example, a person sending an e-mail need not include the entire text of a book in the e-mail. Instead, they can include the ISBN of the book, and interested persons can then use the number to get information about the book - or even the book itself. The ISBN is the primary-key of the book, and it is used as a foreign-key in the e-mail. The use of a foreign key often assumes its existence as a Primary Key somewhere else. Improper foreign key/ Primary Key relationships are the source of many database problems (see Referential Integrity ). A Foreign Key Constraint is a Constraint that data which serves as a foreign key in one Database Record cannot be removed as there is still data in another record that assumes its existence. SEE ALSO |
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