A foreign key is used to establish relationships among relations in the relational model. Technically, a foreign key is a column (or columns) appearing in one relation that is (are) the primary key of another table. Although there may be exceptions, the values in the foreign key columns usually must correspond to values existing in the set of primary key values. This correspondence requirement is created in a database using a referential integrity constraint on the foreign key.
Use of Foreign Key
The use of a foreign key is simply to link the attributes of two tables together with the help of a primary key attribute. Thus, it is used for creating and maintaining the relationship between the two relations.
