Database normalization is crucial for eliminating redundancy and preventing anomalies such as insertion, update, and deletion issues. In this guide, we’ll walk through a sample base table, identify its anomalies, and normalize it step by step into 1NF, 2NF, and 3NF using SQL CREATE TABLE statements.
📌 Base Table

Consider a base table that contains student-course-instructor information:

🚨 Anomalies in the Table

Insertion Anomaly: Cannot add a new course until a student enrolls.

Update Anomaly: Changing an instructor’s email requires updating multiple rows.

Deletion Anomaly: Deleting the last student enrolled in a course removes course and instructor information too.

✅ Step 1: Convert to 1NF (First Normal Form)

Goal: Eliminate repeating groups and ensure all attributes have atomic values.

CREATE TABLE StudentCourses_1NF (
StudentID INT,
StudentName VARCHAR(100),
CourseID VARCHAR(10),
CourseName VARCHAR(100),
Instructor VARCHAR(100),
InstructorEmail VARCHAR(100)
);

✅ Step 2: Convert to 2NF (Second Normal Form)

Goal: Remove partial dependency (attributes depending only on part of a composite key).
Separate the table into Students, Courses, and Enrollments:

CREATE TABLE Students (
StudentID INT PRIMARY KEY,
StudentName VARCHAR(100)
);

CREATE TABLE Courses (
CourseID VARCHAR(10) PRIMARY KEY,
CourseName VARCHAR(100),
Instructor VARCHAR(100),
InstructorEmail VARCHAR(100)
);

CREATE TABLE Enrollments (
StudentID INT,
CourseID VARCHAR(10),
PRIMARY KEY (StudentID, CourseID),
FOREIGN KEY (StudentID) REFERENCES Students(StudentID),
FOREIGN KEY (CourseID) REFERENCES Courses(CourseID)
);

✅ Step 3: Convert to 3NF (Third Normal Form)

Goal: Remove transitive dependency (e.g., InstructorEmail depends on Instructor, not CourseID).
We create a separate Instructors table:

CREATE TABLE Instructors (
InstructorID INT PRIMARY KEY,
InstructorName VARCHAR(100),
InstructorEmail VARCHAR(100)
);

CREATE TABLE Courses (
CourseID VARCHAR(10) PRIMARY KEY,
CourseName VARCHAR(100),
InstructorID INT,
FOREIGN KEY (InstructorID) REFERENCES Instructors(InstructorID)
);
📝 Insert Sample Data

INSERT INTO Students VALUES (1, 'Alice'), (2, 'Bob');

INSERT INTO Instructors VALUES
(1, 'Dr. Smith', 'smith@uni.edu'),
(2, 'Dr. Lee', 'lee@uni.edu'),
(3, 'Dr. Clark', 'clark@uni.edu');

INSERT INTO Courses VALUES
('C101', 'DBMS', 1),
('C102', 'Networks', 2),
('C103', 'AI', 3);

INSERT INTO Enrollments VALUES
(1, 'C101'),
(2, 'C102'),
(1, 'C103');
🔗 Query with JOINS

To list all students along with their courses and instructors:

SELECT s.StudentName, c.CourseName, i.InstructorName
FROM Enrollments e
JOIN Students s ON e.StudentID = s.StudentID
JOIN Courses c ON e.CourseID = c.CourseID
JOIN Instructors i ON c.InstructorID = i.InstructorID;

✅ Key Takeaways

1. Normalization reduces redundancy: Properly structured tables save storage and prevent duplicate data.

2. Avoid anomalies: Normalization prevents insertion, update, and deletion anomalies.

3. Step-wise approach:
   1NF: Ensures atomic values and removes repeating groups.

2NF: Removes partial dependency by separating data into multiple tables.

3NF: Eliminates transitive dependency to ensure each attribute depends only on the primary key.

1. Improved data integrity: Normalized databases are easier to maintain and update.

2. Joins become powerful: Once normalized, SQL joins can easily combine data across tables for meaningful queries.