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Understanding database basics 33
Understanding relational tables
In a database, you can organize data in multiple tables. For example, if you manage a database for
the Human Resource department, you might have one table that lists all the employees
information and another table that lists all the departments:
Because you have multiple departments for employees, but you would not store the information
about the departments in every employee row for several reasons:
•
The department information is the same for each employee in a given department, however,
repeating the department information for each employee is redundant. Storing redundant data
takes up more disk space.
•
If the department information changes, you can update one occurrence. All references to that
department are updated automatically.
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.