Question

Define foreign key. How is this concept useful in relational data model?
Illustrate with suitable example.

Answer 1

Answer

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Explanation:

Answer 2

Foreign key and its usefulness in relational data model

Explanation:

• 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.