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Foreign keys are the column of the table which is used to point to the primary key of another table.In a company, every employee works in a specific department, and employee and department are two different entities. So we can't store the information of the department in the employee table. That's why we link these two tables through the primary key of one table.

We add the primary key of the DEPARTMENT table, Department_Id as a new attribute in the EMPLOYEE table. Now in the EMPLOYEE table, Department_Id is the foreign key, and both the tables are related.

Note: Practically, the foreign key has nothing to do with the primary key tag of another table, if it points to a unique column (not necessarily a primary key) of another table then too, it would be a foreign key. So, a correct definition of foreign key would be: Foreign keys are the columns of a table that points to the candidate key of another table.

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