What is Normalization?
Normalization is a database design technique which organizes tables in a manner that reduces
redundancy and dependency of data.
It divides larger tables to smaller tables and link them using relationships.
Database Normalization Examples -
Assume a video library maintains a database of movies rented out. Without any normalization all
information is stored in one table as shown below.
Table 1
Here you see Movies Rented column has multiple values.
Database Normal Forms
Now let's move in to 1st Normal Forms
1NF (First Normal Form) Rules
Each table cell should contain single value.
Each record needs to be unique.
The above table in 1NF-
1NF Exmple
Table 1 : In 1NF Form
Before we proceed lets understand a few things --
What is a KEY ?
A KEY is a value used to uniquely identify a record in a table. A KEY could be a single column or
combination of multiple columns
Note: Columns in a table that are NOT used to uniquely identify a record are called non-key
columns.
What is a primary Key?
A primary is a single column values used to uniquely identify a database
record.
It has following attributes
A primary key cannot be NULL
A primary key value must be unique
The primary key values can not be changed
The primary key must be given a value when a new record is
inserted.
What is Composite Key?
A composite key is a primary key composed of multiple columns used to identify a record uniquely
In our database , we have two people with the same name Robert Phil but they live at different
places.
Hence we require both Full Name and Address to uniquely identify a record. This is a composite key.
Let's move into second normal form 2NF
2NF (Second Normal Form) Rules
Rule 1- Be in 1NF
Rule 2- Single Column Primary Key
It is clear that we can't move forward to make our simple database in 2nd Normalization form unless
we partition the table above.
Table 1
Table 2
We have divided our 1NF table into two tables viz. Table 1 and Table2. Table 1 contains member
information. Table 2 contains information on movies rented.
We have introduced a new column called Membership_id which is the primary key for table 1.
Records can be uniquely identified in Table 1 using membership id
Database - Foreign Key
In Table 2, Membership_ID is the foreign Key
Foreign Key references primary key of another Table!It helps
connect your Tables
A foreign key can have a different name from its primary key
It ensures rows in one table have corresponding rows in
another
Unlike Primary key they do not have to be unique. Most often
they aren't
Foreign keys can be null even though primary keys can not
Why do you need a foreign key ?
Suppose an idiot inserts a record in Table B such as
You will only be able to insert values into your foreign key that exist in the unique key in the parent
table. This helps in referential integrity.
The above problem can be overcome by declaring membership id from Table2 as foreign key of
membership id from Table1
Now , if somebody tries to insert a value in the membership id field that does not exist in the parent
table , an error will be shown!
What is a transitive functional dependencies?
A transitive functional dependency is when changing a non-key column , might cause any of the
other non-key columns to change
Consider the table 1. Changing the non-key column Full Name , may change Salutation.
Let's move ito 3NF
3NF (ThirdNormal Form) Rules
Rule 1- Be in 2NF
Rule 2- Has no transitive functional dependencies
To move our 2NF table into 3NF we again need to need divide our table.
3NF Example
TABLE 1
Table 2
Table 3
We have again divided our tables and created a new table which stores Salutations.
There are no transitive functional dependencies and hence our table is in 3NF
In Table 3 Salutation ID is primary key and in Table 1 Salutation ID is foreign to primary key in
Table 3
Now our little example is in a level that cannot further be decomposed to attain higher forms of
normalization. In fact it is already in higher normalization forms. Separate efforts for moving in to
next levels of normalizing data are normally needed in complex databases. However we will be
discussing about next levels of normalizations in brief in the following.
Boyce Codd Normal Form (BCNF)
Even when a database is in 3rd Normal Form, still there would be anomalies resulted if it has more
than one Candidate Key.
Sometimes is BCNF is also referred as 3.5 Normal Form.
4NF (Fourth Normal Form) Rules
If no database table instance contains two or more, independent and multivalued data describing the
relevant entity , then it is in 4th Normal Form.
5NF (Fifth Normal Form) Rules
A table is in 5th Normal Form only if it is in 4NF and it cannot be decomposed in to any number of
smaller tables without loss of data.
6NF (Sixth Normal Form) Proposed
6th Normal Form is not standardized yet however it is being discussed by database experts for some
time. Hopefully we would have clear standardized definition for 6th Normal Form in near future.
That's all to Normalization!!!
Summary
Database designing is critical to the successful implementation of a database management system
that meets the data requirements of an enterprise system.
Normalization helps produce database systems that are cost effective, cost effective and have
better security models.
Functional dependencies are a very important component of the normalize data process
Most database systems are normalized database up to the third normal forms.
A primary uniquely identifies are record in a Table and cannot be null
A foreign key helps connect table and references a primary key
