Normalization in SQL for Freshers: Easy Guide with Examples

Normalization is the process of organizing data in a database so that:

1. Data is stored efficiently (no repetition).
2. Data is consistent (no errors or conflicts).
3. Easy to update, insert, or delete data without issues.

Think of it like arranging your room:

• Don’t keep the same book in 5 places (redundancy).
• Keep things in proper boxes (tables) so you can find them easily.

Why Do We Normalize?

• To remove duplicate data
• To avoid data anomalies (like mistakes when updating or deleting)
• To make database maintenance easy

Types of Normalization (Normal Forms)

Normalization is done in steps called Normal Forms (NF).

First Normal Form (1NF)

• Each column should have atomic (single) values.
• No repeating groups or arrays in a column.

Example:

Bad table:

student_id	name	subjects
1	Ramesh	Maths, Science
2	Priya	Arts, Maths

1NF Table:

student_id	name	subject
1	Ramesh	Maths
1	Ramesh	Science
2	Priya	Arts
2	Priya	Maths

• Each column has only one value now.

Second Normal Form (2NF)

• Already in 1NF.
• Every column must depend fully on the primary key (no partial dependency).

Example:

student_id	subject	teacher_name

• If teacher_name depends only on subject, not student_id, it’s partial dependency → violates 2NF.

Fix (2NF):

• Table 1: Student-Subjects
  | student_id | subject |
  |————|———|
  | 1 | Maths |
• Table 2: Subject-Teacher
  | subject | teacher_name |
  |———|————–|
  | Maths | Mr. Sharma |

Third Normal Form (3NF)

• Already in 2NF.
• No transitive dependency: Non-primary key columns should not depend on other non-primary columns.

Example:

student_id	dept_id	dept_name

• dept_name depends on dept_id, not student_id → violates 3NF.

Fix (3NF):

• Table 1: Students
  | student_id | dept_id |
  |————|——–|
• Table 2: Departments
  | dept_id | dept_name |
  |———|———–|

Quick Summary Table

Normal Form	Rule	Example Fix
1NF	Each column has atomic value	Split multiple subjects into rows
2NF	No partial dependency on part of primary key	Move teacher info to separate table
3NF	No transitive dependency	Move department name to another table

Real-Life Analogy

• 1NF → Keep one book per shelf slot, no stacking.
• 2NF → Don’t write teacher’s name on each student’s book, keep a separate teacher list.
• 3NF → Don’t write department name in every student’s record, keep a separate department table.

Super Simple Memory Trick

Normalization = Organizing your database neatly

• 1NF → One value per column
• 2NF → Every column depends fully on primary key
• 3NF → No column depends on another non-key column