Database Normalization: 2NF

Second Normal Form (2NF) is a step in database normalization that builds upon the First Normal Form (1NF). It aims to eliminate partial dependencies to reduce redundancy and improve data integrity.

✅ 1. Requirements for 2NF

A table is in Second Normal Form if:

1. It is already in First Normal Form (1NF).
2. Every non-prime attribute is fully functionally dependent on the entire primary key, not just a part of it.

🔍 Key Concepts

• 1NF: All values are atomic (no arrays, repeating groups).
• Partial Dependency: A non-prime attribute depends on part of a composite key.
• Non-prime Attribute: A column that is not part of any candidate key.

📊 Example

🚫 Not in 2NF

• Primary Key: (StudentID, CourseID)
• StudentName depends only on StudentID
• CourseName depends only on CourseID

Problem: StudentName and CourseName have partial dependencies, violating 2NF.

✅ In 2NF (After Decomposition)

1. Student Table: | StudentID | StudentName | |-----------|-------------| | 1 | Alice | | 2 | Bob |

2. Course Table: | CourseID | CourseName | |----------|------------| | CS101 | Database | | MA201 | Algebra |

3. Enrollment Table: | StudentID | CourseID | |-----------|----------| | 1 | CS101 | | 2 | CS101 | | 1 | MA201 |

🧠 Summary