What is normalization? Dot Net Interview Questions

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It is set of rules that has been established to aid in the design of tables that are meant to be connected through relationships. This set of rules is known as Normalization.

Benefits of Normalizing your database include:

1. Avoiding repetitive entries.

2. Reducing required storage space.

3. Preventing the need to restructure existing tables to accommodate new data.

4. Increased speed and flexibility of queries, sorts, and summaries.


Following are the three normal forms :-

First Normal Form

For a table to be in first normal form, data must be broken up into the smallest units possible.In addition to breaking data up into the smallest meaningful values, tables in first normal form should not contain repetitions groups of fields.

Repeating groups example

For in the above example city1 and city2 are repeating.In order this table to be in First normal form you have to modify the table structure as follows.Also not that the Customer Name is now broken down to first name and last name (First normal form data should be broken down to smallest unit).

Customer table normalized to first normal form

Second Normal form

The second normal form states that each field in a multiple field primary keytable must be directly related to the entire primary key. Or in other words,each non-key field should be a fact about all the fields in the primary key.

In the above table of customer , city is not linked to any primary field.

Normalized customer table.

City is now shifted to a different master table. 

That takes our database to a second normal form. 

Third normal form
A non-key field should not depend on other Non-key field.The field "Total" is dependent on "Unit price" and "qty".

Fill third normal form

So now the "Total" field is removed and is multiplication of Unit price * Qty.