Functional Dependencies in DBMS

1. What is Functional Dependency (FD)?

👉 A relationship where one column (or set of columns) determines another.

• Example: Roll_No → Name (Knowing Roll_No gives Name).

---

2. Key Terms

• Determinant = the predictor (e.g., Roll_No).
• Dependent = the predicted (e.g., Name).

---

3. Why FD is Important?

✔ Removes redundancy
✔ Prevents anomalies (update/insert/delete problems)
✔ Helps normalize tables

---

4. Types of FD

• Trivial: {A, B} → A (dependent is part of determinant).
• Non-Trivial: A → B (dependent not part of determinant).

---

5. Keys & Closure

• Candidate Key = Smallest set of columns that uniquely identify rows.
  Example: Roll_No.
• Closure = All attributes you can find from a key.
  Example: Roll_No⁺ = {Roll_No, Name, Class}.

---

6. Why Decompose Tables?

Bad tables cause:

• Redundancy (wasted space).
• Update anomaly (change in many rows).
• Insert anomaly (can’t add data without another).
• Delete anomaly (deleting one row loses other info).

---

7. How to Decompose?

• Lossless decomposition → No data is lost when splitting.
• Dependency preservation → FDs still hold in decomposed tables.

---

8. Normal Forms (NF)

• 1NF → No repeating groups, atomic values.
• 2NF → No partial dependency (non-key column depends on part of key).
• 3NF → No transitive dependency (non-key depends on another non-key).
• BCNF → Every determinant must be a candidate key.

---

9. Steps to Solve FD Questions

1. Find candidate keys.
2. Find FDs.
3. Check normal form (1NF → 2NF → 3NF → BCNF).
4. Decompose if needed (lossless + dependency preserved).

---

10. Easy Memory Trick 🚀

FD = If I know this → I know that

Keys unlock the table

Normalize step by step:

BCNF → Determinant must be a key

1NF → Remove repeating data

2NF → Remove partial dependency

3NF → Remove transitive dependency

---

• X
• Instagram
• WhatsApp