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== In database systems ==
While different in nature, data redundancy also occurs in [[Relational database management system|database systems]] that have values repeated unnecessarily in one or more records or [[Field (computer science)|fields]], within a [[Table (information)|table]], or where the field is replicated/repeated in two or more tables. Often this is found in [[Unnormalized form|
For instance, when customer data are duplicated and attached with each product bought, then redundancy of data is a known source of [[Consistency (database systems)|inconsistency]] since a given customer might appear with different values for one or more of their attributes.<ref name="DoornRivero2002">{{cite book|author1=Jorge H. Doorn|author2=Laura C. Rivero|title=Database integrity: challenges and solutions|url=https://books.google.com/books?id=fJWncL6mjnwC&pg=PA4|access-date=23 January 2011|year=2002|publisher=Idea Group Inc (IGI)|isbn=978-1-930708-38-9|pages=4–5}}</ref> Data redundancy leads to [[Data corruption|data anomalies and corruption]] and generally should be avoided by design;<ref name="RobCoronel2009">{{cite book|author1=Peter Rob|author2=Carlos Coronel|title=Database systems: design, implementation, and management|url=https://books.google.com/books?id=gCzfjlWOVAAC&pg=PA88|access-date=22 January 2011|year=2009|publisher=Cengage Learning|isbn=978-1-4239-0201-0|page=88}}</ref> applying [[database normalization]] prevents redundancy and makes the best possible usage of storage.<ref name="LimitedItl2009">{{cite book|author1=I. T. L. Education Solutions Limited|author2=Itl|title=Introduction to Information Technology|url=https://books.google.com/books?id=ib2MI6_B9qYC&pg=PA522|access-date=4 February 2011|year=2009|publisher=Pearson Education India|isbn=978-81-7758-118-8|page=522}}</ref>
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