Normalization In Sql Server

Introduction

Normalization is Nothing but efficiently organizing the data in SQL Server.
Its very easy to understand when data in a table is simple and well-organised That is what Normalization do.

Structuring of data can be of 2 types.

Normalization
De-Normalization

See the below image (Fig-1).

Fig-1

Lets Started

In this article we will discuss "Normalization" and why this is important.

Normalization is nothing but simplifying the records , in other we can say we make a table as simple as possible by removing the odd one. So that its very easy to understand the purpose of the each table.

Here we will discuss most widely used Normal Forms(NF-1,NF-2,NF-3).

Lets take an example of the below table. The table consists of Employee data as well as their department details.

We can see the EName column contains the name of the employee which consists of more than one employee in a single record. e.g. - RAJU,ABHI. Which is not the correct way to represent because which may cause problem while complex calculation in future.
So each employee should have their individual data.

TABLE1

*EName*	*Salary Monthly*	*Salary Yearly*	*DEPT NAME*
*RAJU,ABHI*	*12000*	*144000*	HR
*AKU,RAVI,RAKESH*	*10000*	*120000*	*FINANCE*
*RAJ*	*20000*	*240000*	*EDUCATION*
*SANU*	*11000*	*132000*	IT
*MUNU*	*9000*	*108000*	*ADMIN*

FIRST NORMALIZATION FORM(NF-1)

As per the 1st Normal form a table can not hold multiple values . It should have atomic values.
See the below table(TABLE2) EName contains the atomic values(single values) unlike the TABLE1.

TABLE2

Eid	EName	Salary Monthly	Salary Yearly	DEPT NAME
1	RAJU	12000	144000	HR
2	AKU	10000	120000	FINANCE
3	RAJ	20000	240000	EDUCATION
4	SANU	11000	132000	IT
5	MUNU	9000	108000	ADMIN
6	ABHI	12000	144000	HR
7	RAVI	10000	120000	FINANCE
8	RAKESH	10000	120000	FINANCE

But we can see the above table contains Lots of redundant data . Lets normalize the table better with the help of 2ND NORMALIZATION FORM.

SECOND NORMALIZATION FORM(NF-2)

It says

It should fulfill 1st Normalization form .
Non-key columns should be fully and functionally dependent on the primary key of the table.

In TABLE2 see the Dept Name column is not directly dependent on the primary key. So we break the tables into two tables as below.

Employee
Department

Department

Dept id
1	HR
2	FINANCE
3	EDUCATION
4	IT
5	ADMIN

Employee

eid	EName	Salary Monthly	Salary Yearly	Dept id
1	RAJU	12000	144000	1
2	AKU	10000	120000	2
3	RAJ	20000	240000	3
4	SANU	11000	132000	4
5	MUNU	9000	108000	5
6	ABHI	12000	144000	1
7	RAVI	10000	120000	2
8	RAKESH	10000	120000	2

As Department is not directly dependent to the Employee table, we break the table table into two parts as above and associated the two table by using Dept id.
The above table Satisfy NF-2.

Here we can see still some redundant data are available in Employee table. Lets Understand how we can get rid of it by using Third Normalization Form(NF-3)

THIRD NORMALIZATION FORM(NF-3)

This says

It should follow NF-1 and NF-2.
It should not have dependency between the non key columns.

As the Employee table above satisfy both NF-1 and NF-2 , but not NF-3 we need to check how can we satisfy NF-3 by modifying the table.

Lets take Salary Monthly and Salary Yearly. Both are non key columns and both are related. We can say both are directly proportional to each other.

Salary Monthly=Salary Yearly*12

if we have one column we can calculate the other without any problem.

So its better to remove "Yearly Salary".

We can find a table as below.

Employee

eid	EName	Salary Monthly	Dept id
1	RAJU	12000	1
2	AKU	10000	2
3	RAJ	20000	3
4	SANU	11000	4
5	MUNU	9000	5
6	ABHI	12000	1
7	RAVI	10000	2
8	RAKESH	10000	2

Department

Dept id
1	HR
2	FINANCE
3	EDUCATION
4	IT
5	ADMIN

The Above both the table satisfy NF-3. These table will satisfy NF-1,NF-2,NF-3.

Points to remember while using Normalization

Performance will decrease when Joining takes place.

Need to create lots of key to achieve this .

Need to divide single table to multiple table.

Thanks................