What is database redundancy?

Question

Recently in my college database discipline came up this question from which I was left with much doubt.

Answer 1

Redundancy is when a data/information is stored more than once unnecessarily within a database, a gross example:

employee name and person name, each in a different entity, this is redundancy, because if I have an employee who is a person, I will be storing twice the same information within the Bank.

But how to avoid redundancies?

Applying the normal shapes to the design, usually the first three are already sufficient (1FN, 2FN and 3FN)

Answer 2

It has already been said that redundancy is having the same information in two different places.

To define a little better what is the same information in two places take a balance and the account movement, there is redundant information there. By the movement you have the balance. Is this redundancy bad? No. Gives more performance like this and simplifies access.

Take the customer’s data from an issued invoice. It’s the same as the one in the customer’s register. This is redundant, is it bad? No, it’s critical because if you change customer data you can’t change the issued invoice.

There are a number of situations that redundancy is part of the model, even to give more robustness and reliability, in addition to the questions already mentioned.

Redundancy brings the problem that it takes some coordination to maintain consistency. It must be avoided when it is not necessary, so there is the normalization.