What is foreign keys in relational data base?

Foreign key in what is java.

What is foreign key in SQL?

We use foreign key to match column in one  table to primary key in column in another table either it is
one  to one relation or many to one.This foreign key can be used to cross reference table.

Many database or data modelling will be in problem if relation of foreign key is not done properly.

In one table , it can be many foreign keys and it is independently by the database system.Each key can have
different reference tables.