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Definition: Data Redundancy
Data redundancy generally means the duplication of data or repetition of data at more than one location. This term is generally used in databases where some fields/rows are repeated in two or more tables. The duplication of data causes anomaly/distortion in the result fetched when some query is fired.
This can be explained by the following example. Consider the following information stored in 3 tables of a particular database.
Ashish, 25, Intern
Ashish , Delhi, Intern
Ashish, 25, Unmarried
Clearly three tables have got similar type of fields which can be stored in a single table. Storing such type of redundant data results in growth of database size, inconsistent search results and hence reduces efficiency of database search.
In relational database systems this problem is tackled by normalization. 1NF (first normal form) and 2NF (second normal form) is used to remove redundant data by performing various operations on database tables. 1NF enables us to avoid similar data in multiple fields of a table. 2NF enforces data dependency through primary keys and foreign keys.