I always ask question about Third Normal Form in interviews I take.
Q. What is Third Normal Form and what is its advantage?
A. Third Normal Form (3NF) is most preferable normal form in RDBMS. Normalization is the process of designing a data model to efficiently store data in a database. The rules of 3NF are mentioned here
- Make a separate table for each set of related attributes, and give each table a primary key.
- If an attribute depends on only part of a multi-valued key, remove it to a separate table
- If attributes do not contribute to a description of the key, remove them to a separate table.
Normalization is very close to concept of object oriented schema’s and it stores one data at only one place by removing all the redundant data. It also helps to draw the schema easier. Normalization comes at the cost of performance.
Reference : Pinal Dave (http://blog.SQLAuthority.com) , DataModel.org.