Data redundancy occurs in database systems

Relational database management system

A relational database management system is a database management system that is based on the relational model as introduced by E. F. Codd. Most popular databases currently in use are based on the relational database model....

 which have a field that is repeated in two or more tables

Table (information)

A table is a means of arranging data in rows and columns.Production % of goalNorth 4087102%South 4093110% The use of tables is pervasive throughout all communication, research and data analysis. Tables appear in print media, handwritten notes, computer software, architectural...

. For instance, in case when customer data is duplicated and attached with each product bought then redundancy of data is a known source of inconsistency, since customer might appear with different values for given attribute. Data redundancy leads to data anomalies and corruption

Data corruption

Data corruption refers to errors in computer data that occur during writing, reading, storage, transmission, or processing, which introduce unintended changes to the original data...

 and generally should be avoided by design. Database normalization

Database normalization

In the design of a relational database management system , the process of organizing data to minimize redundancy is called normalization. The goal of database normalization is to decompose relations with anomalies in order to produce smaller, well-structured relations...

 prevents redundancy and makes the best possible usage of storage. Proper use of foreign key

Foreign key

In the context of relational databases, a foreign key is a referential constraint between two tables.A foreign key is a field in a relational table that matches a candidate key of another table...

s can minimize data redundancy and chance of destructive anomalies. However sometimes concerns of efficiency and convenience can result redundant data design despite the risk of corrupting the data.

See also

• Data maintenance
  Data maintenance
  Data maintenance is the adding, deleting, changing and updating of binary and high-level files, and the real world data associated with those files. Data can be maintained manually and/or through an automated program, but at origination and translation/delivery point must be translated into a...
  
  
• Data deduplication
  Data deduplication
  In computing, data deduplication is a specialized data compression technique for eliminating coarse-grained redundant data. The technique is used to improve storage utilization and can also be applied to network data transfers to reduce the number of bytes that must be sent across a link...
  
  
• Error detection and correction
  Error detection and correction
  In information theory and coding theory with applications in computer science and telecommunication, error detection and correction or error control are techniques that enable reliable delivery of digital data over unreliable communication channels...
  
  
• Redundancy (engineering)
  Redundancy (engineering)
  In engineering, redundancy is the duplication of critical components or functions of a system with the intention of increasing reliability of the system, usually in the case of a backup or fail-safe....
  
  
• Redundancy (information theory)
  Redundancy (information theory)
  Redundancy in information theory is the number of bits used to transmit a message minus the number of bits of actual information in the message. Informally, it is the amount of wasted "space" used to transmit certain data...