About relational tables

In a database, you can organize data in multiple tables. For example, if you manage a database for the Human Resources department, you might have one table that lists all the information about employees and another table that lists all the departments:


This image shows the relationship between department and employee tables.

You have multiple departments for employees, but you would not store the information about the departments in every employee row for the following reasons:

Storing multiple occurrences of the same data is rarely a good thing. Good relational database design separates application entities into their own tables. Key values from one table are often stored in a related table rather than repeating the information. The key value is used to join the data between the tables to return the complete set of data required.