What is data redundancy?

Data redundancy is a situation where the same information is stored in a database in several places at once.

#The main points

1. Causes of redundancy

• Repeating data across different tables unnecessarily.
• The database not being normalized.

2. Problems redundancy causes

• Update errors: if data changes in one place but not the others, an inconsistency shows up.
• Wasted storage: duplicate records take up extra space.
• Harder maintenance: it's harder to manage, search, and analyze the information.

3. Example

• The Employees table has a DepartmentName field, and a separate Departments table also stores DepartmentName.
• If a department's name changes, it has to be changed in two places, which risks errors.

Put simply, redundancy is unnecessary repetition of data, which creates problems with consistency and how efficiently the database works.