What is DeNormalization, when and where it is used.

Denormalization is the process of undoing the normalization done in a typical database design.t means allowing for redundant data to reduce the number of multi-table (or view) joins necessary. Denormalization is ideal for reporting (OLAP) systems.
Example:
suppose you have normalized territory table in to two tables which having one to many

Territory(territory_No,territory_Name,territory_Qtr1sales_Location)
TerritorySales(territory_No,territory_Qtr,territory_sales);

now suppose if you want to get the data like territory_No,territory_Location,territory_sales then you have to join two tables which is an overhead ,so in this case we do denormalization instead of joining of the tables/views etc

Denormalized territory table contains (territory_No,territory_Name,territory _Location,territory_Qtr1sales,territory_Qtr2sales,territory_Qtr3sales,territory_Qtr4sales );

http://en.wikipedia.org/wiki/Denormalization

Thanks and Regards
V.SaratChand
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Vasanthmvp, if this helps please login to Mark As Answer. | Alert Moderator

Hi Sarath,
Thanks for the reply. In the above mentioned example..
we are unnecessarily getting all the columns data that are not required to us too..
The o/p shown is just similar to Union of two tables. Can you be more clear on this.. Including some records into the table..
Apply Normalization to it, show me a case where this should be applied and after applying de normalization.. what is the difference..

Regards,

Awesome Coding !! :)

Vasanthmvp, if this helps please login to Mark As Answer. | Alert Moderator

ya we may get the result using the union/joins also but they effect the system performance
kindly check these links you may get a good idea
http://ask.sqlservercentral.com/questions/1625/what-is-denormalization.html
http://www.thoughtclusters.com/2009/03/understand-normalization-before-denormalizing/
http://www.dotnetspider.com/forum/85686-normalization-denormalization.aspx

Thanks and Regards
V.SaratChand
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Vasanthmvp, if this helps please login to Mark As Answer. | Alert Moderator