Normalization In SQL

Normalization In SQL,MY SQL and Oracle

What is normalization ?

Defination : Normalization is the process of efficiently organizing data in a database.

There are two goals of the normalization process: 

1. eliminating redundant data (for example, storing the same data in more than one table) and 

2. 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 :
Eliminate data redundancy
Improve performance
Query optimization
Faster update due to less number of columns in one table
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             1          488-511-3258
2     Bob    102     2                                                    2             1         781-896-9897
3     Rob    201     3                                                    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