Database Normalization: First, Second, and Third Normal

What is Normalization in SQL ?

 What is normalization ?

Defination : Normalization is the process of efficiently organizing data in a database. There are two goals of the normalization process: eliminating redundant data (for example, storing the same data in more than one table) and ensuring data dependencies make sense (only storing related data in a table). Both of these are worthy goals as they reduce the amount of space a database consumes and ensure that data is logically stored. There are several benefits for using Normalization in Database.
Benefits :

1. Eliminate data redundancy
2. Improve performance
3. Query optimization
4. Faster update due to less number of columns in one table
5. Index improvement

There are diff. - diff. types of Normalizations form available in the Database. Lets see one by one.
1. First Normal Form (1NF)
 First normal form (1NF) sets the very basic rules for an organized database:

• Eliminate duplicative columns from the same table.
• Create separate tables for each group of related data and identify each row with a unique column or set of columns (the primary key).
• Remove repetative groups
• Create Primary Key

Name	State	Country	Phone1	Phone2	Phone3
John	101	1	488-511-3258	781-896-9897	425-983-9812
Bob	102	1	861-856-6987
Rob	201	2	587-963-8425	425-698-9684
PK			[ Phone Nos ]
?				?
ID	Name	State	Country	Phone
1	John	101	1	488-511-3258
2	John	101	1	781-896-9897
3	John	101	1	425-983-9812
4	Bob	102	1	861-856-6987
5	Rob	201	2	587-963-8425
6	Rob	201	2	425-698-9684

2. Second Normal Form (2NF)Second normal form (2NF) further addresses the concept of removing duplicative data:

·         Meet all the requirements of the first normal form.

·         Remove subsets of data that apply to multiple rows of a table and place them in separate tables.

·         Create relationships between these new tables and their predecessors through the use of foreign keys.   

Remove columns which create duplicate data in a table and related a new table with Primary Key – Foreign Key relationship

ID	Name	State	Country	Phone
1	John	101	1	488-511-3258
2	John	101	1	781-896-9897
3	John	101	1	425-983-9812
4	Bob	102	1	861-856-6987
5	Rob	201	2	587-963-8425
6	Rob	201	2	425-698-9684
ID	Name	State	Country		PhoneID	ID	Phone
1	John	101			1	1	488-511-3258
2	Bob	102			2	1	781-896-9897
3	Rob	201			3	1	425-983-9812
					4	2	587-963-8425
					5	3	587-963-8425
					6	3	425-698-9684

3. Third Normal Form (3NF)

Third normal form (3NF) goes one large step further:

·         Meet all the requirements of the second normal form.

·         Remove columns that are not dependent upon the primary key.

  Country can be derived from State also… so removing country

ID	Name	State	Country
1	John	101	1
2	Bob	102	1
3	Rob	201	2

4. Fourth Normal Form (4NF)

Finally, fourth normal form (4NF) has one additional requirement:

·         Meet all the requirements of the third normal form.

·         A relation is in 4NF if it has no multi-valued dependencies.

If PK is composed of multiple columns then all non-key attributes should be derived from FULL PK only. If some non-key attribute can be derived from partial PK then remove it

The 4NF also known as BCNF NF

TeacherID	StudentID	SubjectID	StudentName
101	1001	1	John
101	1002	2	Rob
201	1002	3	Bob
201	1001	2	Rob
TeacherID	StudentID	SubjectID	StudentName
101	1001	1	X
101	1002	2	X
201	1001	3	X
201	1002	2	X