Normalization of Database Table

8/10/2019 Normalization of Database Table

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Normalization of Database

Table


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Normalization is a systematic approach ofdecomposing tables by eliminate data redundancyand undesirable characteristics such as Insertion,Update and Deletion.Two main purpose:

Eliminating redundant (useless) dataEnsuring data dependencies make sense.

Normalization of Database


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Without normalization, it becomes difficult to handleand update the database.Insertion, Updating and Deletion are very frequent ifdatabase is not normalized.

Problem with Normalization


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S_id S_Name S_Address Subject_offered

401 Adam Kuala Lumpur Bio

402 Alex Ipoh Maths

403 Stuart Penang Maths

404 Adam Melacca Physics

Student Table


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A row of data cannot contain repeating group.Each row of data must have a unique identifier.Student_Subject Table

1NF

S_id S_Name Subject_offered

401 Adam Biology

401 Adam Physics

403 Alex Maths

404 Stuart Maths


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You can clearly see that student name Adam is used twice inthe table and subject maths is also repeated.To reduce above table to First Normal form break the tableinto two different tables.New Student Table:

S_id S_Name

401 Adam

403 Alex

404 Stuart


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Subject Table :

In Student table concatenation of subject_id andstudent_id is the Primary key .Now both table are normalized.

Subject_id Student_id Subject_offered

10 401 Biology

11 401 Physics12 402 Maths

12 403 Maths


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A table to be normalized to Second Normal Formshould meet all the needs of First Normal Form andthere must not be any partial dependency.If any column depends only on one part of theconcatenated key, then the table fail Second normal

form.

2NF


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Customer table:

Customer_id and Order_Id is the primary key.However this table are not in the Second Normal Form

because there are partial dependencies of columns onprimary key.

Customer_id Customer_Name Order_Id Order_Name

Sale_Detail

401 Adam 10 Order1 Sale1

401 Adam 11 Order2 Sale2402 Alex 12 Order3 Sale3

403 Stuart 13 order4 sale4


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To reduce Customer table to Second Normal Formbreak the table into following three different table:

Customer Detail TableCustomer_id Customer_Name

101 Adam

102 Alex102 Stuart


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Order Detail Table:

Sale_Detail:

Customer_id Order_id Sale_Detail101 10 Sale1

101 11 Sale2

102 12 Sale3

103 13 sale4

Order_id Order_name

10 Order1

11 Order2

12 Order3

13 Order4


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Third Normal Form applies that every non-primeattribute of table must be dependent on Primary Key.The transitive Functional Dependency should beremoved from the table.Table must be in second form.

3NF


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Student_Detail Table:

In this table Student_id is Primary Key.But street, city and state depends upon zip.

The dependency between zip and other fields is calledtransitive dependency.To apply 3NF we need to move the street, city and state tonew table

Student_Id Student_Name

DOB Street

City State Zip


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The advantages of removing transitive dependency:Amount of data duplication is reducedData integrity achieved.

Student_id Student_Name DOB Zip

Zip Street City State


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Example 1


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CUSTOMER (CustomerNo, CustomerName, Address,ItemCode, ItemDescription, Quantity, Price, Supplier,SupplierName)

Example 2


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OrderNo OrderDate ProductNo Descrption Quantity123 3/8/95 A3

A4

A2

Pen MerahPen Hijau

Pen Kuning

71

4234 5/7/95 A1

A3A1A3

123

345 12/7/95 A3 Pen Merah 144

Example 3

Documents

Normalization of Database Table