What is normalization and different types of norm?

Normalization is a design technique that is widely used as a guide in designing relational databases.

Normalization is essentially a two step process that puts data into tabular form by removing repeating groups and then removes duplicated data from the relational tables (Additional reading recommended).

Redundant data wastes disk space and creates maintenance problems. If data that exists in more than one place must be changed, the data must be changed in exactly the same way in all locations which is time consuming and prone to errors. A change to a customer address is much easier to do if that data is stored only in the Customers table and nowhere else in the database.

Inconsistent dependency is a database design that makes certain assumptions about the location of data. For example, while it is intuitive for a user to look in the Customers table for the address of a particular customer, it may not make sense to look there for the salary of the employee who calls on that customer. The employee's salary is related to, or dependent on, the employee and thus should be moved to the Employees table. Inconsistent dependencies can make data difficult to access because the path to find the data may not be logical, or may be missing or broken.

There are three different types of norm as follows:

  • First Normal Form – A database is said to be in First Normal Form when all entities have a unique identifier or key, and when every column in every table contains only a single value and doesn't contain a repeating group or composite field.
  • Second Normal Form – A database is in Second Normal Form when it is in First Normal Form plus every non-primary key column in the table must depend on the entire primary key, not just part of it, assuming that the primary key is made up of composite columns.
  • Third Normal Form – A database is in Third Normal Form when it is in Second Normal Form and each column that isn't part of the primary key doesn't depend on another column that isn't part of the primary key.


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