In a relational database, you model collections of entities from the real world as tables . An entity can be anything for which you want to record information; typically important objects and events. For example, in a retail system example, you might create tables for customers, products, orders, and line items within an order. A table contains rows, and each row represents a single instance of an entity. Which two keys are needed to create a one-to-many relationship between two tables in a relational database?