http://www.sqlservercentral.com/blogs/abhijit_desai/2010/09/07/noramlization/

Printed 2014/08/20 03:11PM

What is Normalization in SQL ?

By yrs_abhishek, 2010/09/07

=> 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:

 

           
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

 


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