Imagine moving money between two accounts: the withdrawal succeeds but the deposit fails. Without protection, the data is now wrong. A transaction groups several statements into one all-or-nothing unit, using BEGIN, COMMIT, and ROLLBACK, and the ACID guarantees — atomicity, consistency, isolation, and durability — explain what a database promises you.
Real systems also have many users at once. You'll learn what can go wrong when transactions overlap — dirty, non-repeatable, and phantom reads — and how isolation levels trade safety against speed. You'll also see how locking works and what causes deadlocks, where two transactions wait on each other forever.
Work through the lessons in order, then continue on to Database Design.
Hussein Nasser walks through what a transaction is and each of the ACID properties using concrete examples.
A focused explanation of how transactions group statements together and why that matters for data integrity.
A hands-on MySQL demonstration of starting a transaction, then making changes permanent with COMMIT or undoing them with ROLLBACK.
Explains the problems that overlapping transactions can cause and how each isolation level prevents them.
A step-by-step look at the standard isolation levels and what each one allows or prevents.
A clear explanation of how deadlocks happen when transactions hold locks that each other needs, and why databases have to break them.