1. Foreign key (FK) is a single column or combination of columns that establish and enforce a link between the data in two tables
2. Link is created between two tables when the column or columns that hold the primary key value for one table are referenced by the column or columns in another table. This column becomes a foreign key in the second table.
3.A FOREIGN KEY constraint can reference columns in tables in the same database or within the same table.
4.Purpose of a FOREIGN KEY constraint is to control the data that can be stored in the foreign key table, it also controls changes to data in the primary key table