DataBolt

All Lessons

Introduction to SQL

SQL Lesson 1: Your Sample Database

SQL Lesson 2: SELECT — Reading data

SQL Lesson 3: WHERE — Filtering rows

SQL Lesson 4: AND, OR, NOT

SQL Lesson 5: BETWEEN, IN, LIKE

SQL Lesson 6: NULL — The Mystery Value

SQL Lesson 7: ORDER BY

SQL Lesson 8: LIMIT & OFFSET

SQL Lesson 9: Aggregate Functions

SQL Lesson 10: GROUP BY

SQL Lesson 11: HAVING

SQL Lesson 12: INNER JOINs

SQL Lesson 13: LEFT JOINs

SQL Lesson 14: RIGHT JOINs

SQL Lesson 15: SELF JOINs

SQL Lesson 16: UNION JOINs

SQL Lesson 17: Joining Multiple Tables

SQL Lesson 18: Subqueries

SQL Lesson 19: CTEs (WITH)

SQL Lesson 20: CASE Statements

SQL Lesson 21: Window Functions

SQL Lesson 22: String Functions

SQL Lesson 23: Date & Time Functions

SQL Lesson 24: INSERT, UPDATE, DELETE

SQL Lesson 25: CREATE TABLE & DDL

SQL Lesson 26: Indexes & Performance

SQL Lesson 27: Transactions & ACID

SQL Lesson 28: SQL Execution Order

SQL Lesson 29: 50 Practice Problems

CHAPTER 28

Transactions & ACID

Data integrity — guaranteeing your data is always correct.

IN THIS CHAPTER

What a transaction is and why it matters
START TRANSACTION, COMMIT, ROLLBACK
ACID: Atomicity, Consistency, Isolation, Durability
SAVEPOINT for partial rollbacks

🌟 Think of it this way: A bank transfer: deduct ₹5,000 from Account A, add ₹5,000 to Account B. If the server crashes after the deduction but before the credit, the money disappears. A transaction guarantees either BOTH operations succeed or NEITHER does — the money cannot vanish.

Safe money transfer

START TRANSACTION;
UPDATE accounts SET balance = balance - 5000 WHERE account_id =
101;
UPDATE accounts SET balance = balance + 5000 WHERE account_id =
202;
COMMIT; -- only if both succeed
-- If anything fails:
ROLLBACK; -- reverts both updates completely

Property	Guarantee	Bank Transfer Example
Atomicity	All changes commit or none do	Debit + credit both happen or neither
Consistency	DB remains valid before and after	Total money in system stays the same
Isolation	Concurrent transactions do not interfere	Two simultaneous transfers do not corrupt each other
Durability	Committed data survives crashes	After COMMIT, data is on disk even if power cuts