Redundancy control in databases

Redundancy is the state where duplicate rows of the same data is available in a database.

Lets say we have an employee database which contains 2 rows of the following data

Emp num Emp Name Age

12345 John 25

12345 John 25

This is data redundancy.

Data redundancy can be avoided by the use of keys in tables. If in the employee table we had defined a primary key condition for employee number, then the system would not allow us to enter 2 rows of the same data.