Hello All,

Would you please help me to Define the concept of referential integrity rule for the relational data model and Give specific examples of referential integrity rules and express them in SQL.
and Define functional dependencies and explain how they can be used to improve the design of a relational database and I was thinking what is the third normal form.
and Give an example of a relation in the third normal form to help me to understand it.

Thanks and regards

References Constraint: This is the foreign key constraint as implemented by Oracle. A references constraint is only applied at SQL insert and delete times.
For example, assume a one-to-many relationship between the EMPLOYEE and DEPENDENT tables; each employee may have many dependents, yet each dependent belongs to only one employee. The references constraint tells Oracle at insert time that the value in DEPENDENT.emp_num must match the EMPLOYEE.emp_num in the employee row, thereby ensuring that a valid employee exists before the dependent row is added.
At SQL delete time, the references constraint can be used to ensure that an employee is not deleted, if rows still exist in the DEPENDENT table.

The term referential integrity simply means that if a row in a table has a pointer to a row in another table, the row in the table that is pointed at, must be exist.
Said another way, you should not remove a row which contains information that other row(s) depend on.

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