Denormalization
Denormalization on the contrary is the process of adding redundant data to speed up complex queries involving multiple table JOINS. Data is included in one table from another in order to eliminate the second table which reduces the number of JOINS in a query and thus achieves performance.
Only one valid reason exists for denormalizing a relational design - to enhance performance. The sacrifice to performance is that you increase redundancy in a database.
References:
http://www.indiabix.com/technical/dbms-basics/7
http://www.techpreparation.com/mysql-interview-questions-answers1.htm
http://www.dotnetfunda.com/interview/exclusive/showcatquestion.aspx?category=38
In computing, denormalization is the process of attempting to optimise the read performance of a database by adding redundant data or by grouping data.[1][2] In some cases, denormalisation helps cover up the inefficiencies inherent in relational database software. A relational normalised database imposes a heavy access load over physical storage of data even if it is well tuned for high performance.
http://en.wikipedia.org/wiki/Denormalization
Denormalization means allowing redundancy in a table. The main benefit of denormalization is improved performance with simplified data retrieval and manipulation. This is done by reduction in the number of joins needed for data
