MySQL Transactions

How it works

A transaction groups changes into an atomic unit. COMMIT makes its successful work durable under the server’s durability configuration; ROLLBACK cancels its transactional changes. This example deliberately changes a quantity and then rolls it back, showing that the original stock remains. A real reservation might change inventory and insert a matching record in the same transaction, with failure handling that rolls back both.

Run in a disposable MySQL lab

Use Oracle MySQL 8.4 with InnoDB, not Bhylu’s SQLite playground. The examples were reviewed on MySQL 8.4.8. XAMPP may provide MariaDB, which has different feature and collation behaviour. Check your actual server before running the script. These lessons do not require a change to Bhylu’s PHP, Apache or normal database service.

1. On a separate lab instance, create the empty bhylu_mysql_lab schema. Stop if it already exists; do not overwrite an existing database.
2. Select that schema and import the complete repair-parts seed once. It sets the documented session mode, utf8mb4 collation, UTC and English date-name locale.
3. Run this lesson in a fresh copy of the seed, not after another lesson’s writes. Use the command-line client or a compatible editor. DELIMITER lines are client instructions for stored-program examples.

Download this complete lesson script. Its setup is the linked seed; review the dataset before changing it. Administrative and destructive examples are restricted to the specifically named disposable objects. Every script repeats the session settings because each new connection has its own session. No MySQL browser runner is currently available.

Example

SET NAMES utf8mb4 COLLATE utf8mb4_0900_ai_ci;
SET SESSION sql_mode = 'STRICT_TRANS_TABLES,ONLY_FULL_GROUP_BY,ERROR_FOR_DIVISION_BY_ZERO,NO_ENGINE_SUBSTITUTION';
SET SESSION time_zone = '+00:00';
SET SESSION lc_time_names = 'en_US';
START TRANSACTION;
UPDATE parts SET quantity = quantity - 2 WHERE id = 1 AND quantity >= 2;
ROLLBACK;
SELECT quantity FROM parts WHERE id = 1;

Expected result

12

The stock is twelve again. Every participating table must use an appropriate transactional engine, and DDL has separate implicit-commit rules. Keep transactions short so locks are not held while a user reads a page or an application waits for unrelated network services. A connection pool must not return a connection with an unfinished transaction to another request.