📘 Database Normalization Example (1NF 3NF) with SQL in Oracle Live SQL

#computerscience #database #tutorial #sql

In this post, we’ll take a Student–Course–Instructor dataset, identify anomalies, and normalize it step by step from 1NF → 3NF, finally writing SQL queries and testing them in Oracle Live SQL.

🔎 The Raw Table

We start with this table:

⚠️ Anomalies in the Design

Insertion anomaly – Cannot insert a new course unless a student enrolls.
Update anomaly – Updating an instructor’s phone requires changing multiple rows.
Deletion anomaly – If Priya drops DBMS, we lose Dr. Kumar’s info.

✅ Step 1: 1NF

The table is already in 1NF (atomic values).

CREATE TABLE StudentCourse (
    StudentID VARCHAR2(10),
    StudentName VARCHAR2(50),
    CourseID VARCHAR2(10),
    CourseName VARCHAR2(50),
    Instructor VARCHAR2(50),
    InstructorPhone VARCHAR2(15),
    PRIMARY KEY (StudentID, CourseID)
);

✅ Step 2: 2NF

We remove partial dependencies:

StudentID → StudentName
CourseID → CourseName, Instructor, InstructorPhone

So we split into Student, Course, Enrollment.

CREATE TABLE Student (
    StudentID VARCHAR2(10) PRIMARY KEY,
    StudentName VARCHAR2(50)
);

CREATE TABLE Course (
    CourseID VARCHAR2(10) PRIMARY KEY,
    CourseName VARCHAR2(50),
    Instructor VARCHAR2(50),
    InstructorPhone VARCHAR2(15)
);

CREATE TABLE Enrollment (
    StudentID VARCHAR2(10),
    CourseID VARCHAR2(10),
    PRIMARY KEY (StudentID, CourseID),
    FOREIGN KEY (StudentID) REFERENCES Student(StudentID),
    FOREIGN KEY (CourseID) REFERENCES Course(CourseID)
);

✅ Step 3: 3NF

Now we remove transitive dependency: InstructorPhone depends on Instructor, not directly on Course.

So we create a separate Instructor table.

CREATE TABLE Instructor (
    InstructorID NUMBER PRIMARY KEY,
    InstructorName VARCHAR2(50),
    InstructorPhone VARCHAR2(15)
);

CREATE TABLE Course (
    CourseID VARCHAR2(10) PRIMARY KEY,
    CourseName VARCHAR2(50),
    InstructorID NUMBER,
    FOREIGN KEY (InstructorID) REFERENCES Instructor(InstructorID)
);

CREATE TABLE Student (
    StudentID VARCHAR2(10) PRIMARY KEY,
    StudentName VARCHAR2(50)
);

CREATE TABLE Enrollment (
    StudentID VARCHAR2(10),
    CourseID VARCHAR2(10),
    PRIMARY KEY (StudentID, CourseID),
    FOREIGN KEY (StudentID) REFERENCES Student(StudentID),
    FOREIGN KEY (CourseID) REFERENCES Course(CourseID)
);

✅ Insert Sample Data

-- Instructors (manual IDs)
INSERT INTO Instructor VALUES (1, 'Dr. Kumar', '9876543210');
INSERT INTO Instructor VALUES (2, 'Dr. Mehta', '9123456780');
INSERT INTO Instructor VALUES (3, 'Dr. Rao', '9988776655');

-- Courses
INSERT INTO Course VALUES ('C101', 'DBMS', 1);
INSERT INTO Course VALUES ('C102', 'Data Mining', 2);
INSERT INTO Course VALUES ('C103', 'AI', 3);

-- Students
INSERT INTO Student VALUES ('S01', 'Arjun');
INSERT INTO Student VALUES ('S02', 'Priya');
INSERT INTO Student VALUES ('S03', 'Kiran');

-- Enrollments
INSERT INTO Enrollment VALUES ('S01', 'C101');
INSERT INTO Enrollment VALUES ('S01', 'C102');
INSERT INTO Enrollment VALUES ('S02', 'C101');
INSERT INTO Enrollment VALUES ('S03', 'C103');

✅ Final Query with JOINs

To list all students with their courses and instructors:

SELECT s.StudentName, c.CourseName, i.InstructorName
FROM Enrollment e
JOIN Student s ON e.StudentID = s.StudentID
JOIN Course c ON e.CourseID = c.CourseID
JOIN Instructor i ON c.InstructorID = i.InstructorID;