Define foreign key. How is this concept useful in relational data model?
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Foreign key and its usefulness in relational data model
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- A foreign key is defined as a key that refers to the primary key column of another table.
- A referential integrity constraint is based on the concept of Foreign Keys. A foreign key is an important attribute of a relation to which other relationships may refer. Restrictive state of referential integrity exists where relationship refers to a key attribute of a different or the same relation.
- Let us consider the two following tables - STUDENT table and BOOKS_ISSUED table. The STUDENT (St_Id, Name, Age, Class) table includes all the STUDENT data and the BOOKS_ISSUED (St_Id, Book_Id, Issue_Dt) table includes all the books issued to the students. Here St_Id in BOOKS_ISSUED is used as a foreign key.
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