A relationship in Database Management System (DBMS) is defined as the way in which two or more data tables or data entities are linked. The data is typically represented in a relational database in the form of tables; where the columns of table represent the type of information all entities possess and row represents a complete record of information for a single entity of table.

There is always a column in a data table that is assigned the primary key for that table and its purpose is to uniquely identify each row of a column. In the below example, the ID column serves the purpose of primary key.

Customer Table