Programming instructions

Understanding database basics 31
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.