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I want to know that what is the normalization, what are the types of normal forms are there. And also that why it is used in datbase?

Ravindra Sachan
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  • That's a broad question with many sources available for explanations. You can start here, for example: https://en.wikipedia.org/wiki/Database_normalization – Guffa Aug 18 '15 at 15:23
  • This is repeated question. –  Oct 12 '15 at 10:04

2 Answers2

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Very briefly, normalization's aim is to avoid data redundancy, storing once each distinct information that can be referenced by many, creating different kinds of data relationships as one-to-one, one-to-many, many-to-many.

Simimmo
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Normalization

If a database design is not perfect, it may contain anomalies, which are like a bad dream for any database administrator. Managing a database with anomalies is next to impossible. The following are the types of anomalies.

  1. Update anomalies
  2. Deletion anomalies
  3. Insert anomalies

Update anomalies:- 

  If data items are scattered and are not linked to each other properly,

then it could lead to strange situations. For example, when we try to update one data item having its copies scattered over several places, a few instances get updated properly while a few others are left with old values. Such instances leave the database in an inconsistent state.

Deletion anomalies :−

We tried to delete a record, but parts of it was left undeleted because of unawareness, the data is also saved somewhere else.

Insert anomalies :−

We tried to insert data in a record that does not exist at all.

Normalization is a method to remove all these anomalies and bring the database to a consistent state.

First Normal Form

First Normal Form is defined in the definition of relations (tables) itself. This rule defines that all the attributes in a relation must have atomic domains. The values in an atomic domain are indivisible units.

Second Normal Form

If we follow second normal form, then every non-prime attribute should be fully functionally dependent on prime key attribute. That is, if X → A holds, then there should not be any proper subset Y of X, for which Y → A also holds true.

Third Normal Form

For a relation to be in Third Normal Form, it must be in Second Normal form and the following must satisfy −

* No non-prime attribute is transitively dependent on prime key attribute.

* For any non-trivial functional dependency, X → A, then either −

       X is a superkey or,

       A is prime attribute.