Chapter 6 database normalisation

transcript

Introduction to MySQLDatabase Normalization

Relevance of normalization

• We could have store all the data in a single table like

• But there are several issues arise here

Emp_id Emp_name Emp_age Emp_email Fk_int_designation

Vchr_Desig_roles

1000 Deepak 45 dk@gmail.com

Are Manager Handles all the district level operations

1001 Aneesh 23 an@gmail.com Sales person Will increase sales and ensure customer satisfaction

1002 Naveen 25 nn@gmail.com

Sales person Will increase sales and ensure customer

satisfaction

1003 Jacob 25 dpk@gmail.com

Administrator Handles all the district level operations

Vchr_Desig_roles

1002 Naveen 25 nn@gmail.com Sales person Will increase sales and ensure customer satisfaction

Here designation is repeated for all the rows and where ever it repeats the designation role also has to repeat. This redundancy takes a lot of space to store and

is inefficient

Vchr_Desig_roles

1002 Naveen 25 nn@gmail.com Sales person Will increase sales and ensure customer satisfaction

Suppose if i want to modify the roles of any designation, i will have to do the same for all records in the table. Its time consuming and not an effective way to follow

Normalization• Normalization is the process of moving data into related

tables

• Will save data dependency and redundancy

• Save typing of repetitive data

• Reduce disk space

Types of Normalization

• There are several levels of normalization– 1st Normalization– 2nd Normalization– 3rd Normalization

First Normal Form

First Normal Form– Each field contains the smallest meaningful value– The table does not contain repeating groups of fields or

repeating data within the same field

To attain 1st normalized form what you have to do is•Create a separate field/table for each set of related data. •Identify each set of related data with a primary key

Table violating 1st Normal Form

Company (pk) Branches

Baabte Cochin, Calicut

baabtra Calicut,Trivandrum

It really is a bad setup that we are storing multiple values in a single column. For a table to be in 1st normalised form it should only have atomic values

Table violating 1st Normal Form

Company (Pk) Branche1 Branch2

Baabte Cochin Calicut

baabtra Calicut Trivandrum

It still in a bad set up , as we should not have multiple columns describing the same property of an entity.

Table conforming to 1st Normal Form

Company (pk) Branch (pk)

Baabte Cochin

Baabte Calicut

baabtra Calicut

baabtra Trivandrum

We have resulted in a 1st normalised table with primary key consists of two columns

Second Normalisation

– usually used in tables with a multiple-field primary key (composite key)

– each non-key field relates to the entire primary key– any field that does not relate to the primary key is placed

in a separate table• To attain 1st normalized form what you have to do is

•eliminate redundant data in a table •Create separate tables for sets of values that apply to

multiple records

Table violating 2nd Normal Form

Employee (pk) Skill (pk) WorkLocation

John IOS programmer Calicut

Mathew Java programmer Cochin

Thomas Android programmer

Trivandrum

Alex PHP programmer Banglore

Ram Java programmer Mumbai

John PHP programmer Delhi

Soozan doNet programmer Calicut

Primary key= { Employee,Skill }

Table violating 2nd Normal Form

Employee (pk) Skill (pk) WorkLocation

John IOS programmer Calicut

Mathew Java programmer Cochin

Trivandrum

Alex PHP programmer Banglore

Ram Java programmer Mumbai

John PHP programmer Delhi

Soozan doNet programmer Calicut

Here non key attribute do not fully depends on compete primary key. IeWorkLocation depends only on Employee and doesn’t depend on Skill (partial

dependency)

Primary key= { Employee,Skill }

Table conforming to 2nd Normal Form

Employee (pk)

Skill (pk)

John IOS programmer

Mathew Java programmer

Alex PHP programmer

Ram Java programmer

John PHP programmer

Soozan doNet programmer

Employee (pk)

WorkLocation

John Calicut

Mathew Cochin

Thomas Trivandrum

Alex Banglore

Ram Mumbai

John Delhi

Soozan Calicut

Third Normalisation

Third Normal Form• Usually used in tables with a single field primary key

--records do not depend on anything other than a table's primary key – each non-key field is a fact about the key– Values in a record that are not part of that record's key do

not belong in the table. In general, any time the contents of a group of fields may apply to more than a single record in the table, consider placing those fields in a separate table.

EMPNO (Primary Key)

FIRSTNAME LASTNAME WORKDEPTNO DEPTNAME

000290 John Parker OP11 Operations

000320 Ramlal Mehta SE21 Software Support

000310 Maude Setright OP11 Operations

Table violating 3rd Normal Form

EMPNO (Primary Key)

FIRSTNAME LASTNAME WORKDEPTNO DEPTNAME

000290 John Parker OP11 Operations

000320 Ramlal Mehta SE21 Software Support

000310 Maude Setright OP11 Operations

Table violating 3rd Normal Form

Here all the fields are not completely depend on Primary key.Ie Dept Name column only depends on DeptNo.And deptno depends on the EMPNO.

Ie its a transitive dependency. Which should be avoided

Table conforming to 3rd Normal Form

EMPNO (Primary Key)

FIRSTNAME LASTNAME WORKDEPTNO

000290 John Parker OP11

000320 Ramlal Mehta SE21

000310 Maude Setright OP11

WORKDEPTNO DEPTNAME

OP11 Operations

SE21 Software Support

OP11 Operations

Here all the fields are completely depend on Primary key.

End of Day2

Chapter 6 database normalisation

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