Why should you care?

Checkout must deduct stock and create order together — half-done state loses money or oversells inventory.

See it live — copy this example

Run in MySQL Workbench or the mysql CLI.

START TRANSACTION;
UPDATE products SET stock_qty = stock_qty - 2 WHERE product_id = 10;
INSERT INTO orders (customer_id, order_ref, total_inr) VALUES (1, 'DF-TX-01', 1598.00);
COMMIT;

What happened?

• Stock drops and order inserts in one transaction.
• If INSERT fails, ROLLBACK restores stock.
• COMMIT makes both changes permanent together.

Practice next

1. Add stock_qty column to products.
2. Run START TRANSACTION; both statements; COMMIT;
3. Repeat but ROLLBACK before COMMIT — verify stock unchanged.
4. Intentionally violate FK on INSERT then ROLLBACK.
5. Use BEGIN alias instead of START TRANSACTION.

Remember

START TRANSACTION begins a unit of work. COMMIT saves; ROLLBACK undoes. Use for multi-step money/inventory changes.

DataFlow checkout

Payment timeout triggers ROLLBACK so stock returns to catalog.

Outcome: No ghost orders or missing inventory.