Las transacciones son un conjunto de instrucciones SQL que tienen la cualidad de ejecutarse como una unidad, es decir, o se ejecutan todas o no se ejecuta ninguna.

1. Transacción comprometida

mysql> begin;
Query OK, 0 rows affected (0.00 sec)

mysql> select * from editoriales;
+-----+---------------+
| ide | nombre |
+-----+---------------+
| 1 | Prentice Hall |
| 2 | Alfaomega |
| 3 | Ra-Ma |
+-----+---------------+
3 rows in set (0.00 sec)

mysql> insert into editoriales values (0,"Trillas");
Query OK, 1 row affected (0.00 sec)

mysql> commit;
Query OK, 0 rows affected (0.01 sec)

mysql> select * from editoriales;
+-----+---------------+
| ide | nombre |
+-----+---------------+
| 1 | Prentice Hall |
| 2 | Alfaomega |
| 3 | Ra-Ma |
| 4 | Trillas |
+-----+---------------+
4 rows in set (0.00 sec)

2. Transacción no completada

mysql> begin;
Query OK, 0 rows affected (0.00 sec)

mysql> delete from libros;
Query OK, 5 rows affected (0.00 sec)

mysql> select * from libros;
Empty set (0.00 sec)

mysql> rollback;
Query OK, 0 rows affected (0.00 sec)

mysql> select * from libros;
+-----+------+--------------------------+------------+
| idl | ide | titulo | fecha |
+-----+------+--------------------------+------------+
| 1 | 2 | Minería de Datos | 2017-11-01 |
| 2 | 3 | Python 3 Curso Práctico | 2017-05-30 |
| 3 | 3 | Unity 2017.X | 2017-10-01 |
| 4 | 2 | Inteligencia Artificial | 2018-01-01 |
| 5 | 2 | Aprender Raspberry Pi | 2017-01-01 |
+-----+------+--------------------------+------------+
5 rows in set (0.00 sec)

3. Inter-Bloqueo

Tiempo	Usuario 1	Usuario 2
1	mysql> begin; Query OK, 0 rows affected (0.00 sec) mysql> delete from libros; Query OK, 5 rows affected (0.00 sec) mysql> select * from libros; Empty set (0.00 sec)
2		mysql> begin; Query OK, 0 rows affected (0.00 sec) mysql> select * from libros; +-----+------+--------------------------+------------+ | idl | ide | titulo | fecha | +-----+------+--------------------------+------------+ | 1 | 2 | Minería de Datos | 2017-11-01 | | 2 | 3 | Python 3 Curso Práctico | 2017-05-30 | | 3 | 3 | Unity 2017.X | 2017-10-01 | | 4 | 2 | Inteligencia Artificial | 2018-01-01 | | 5 | 2 | Aprender Raspberry Pi | 2017-01-01 | +-----+------+--------------------------+------------+ 5 rows in set (0.00 sec) mysql> delete from libros; ERROR 1205 (HY000): Lock wait timeout exceeded; try restarting transaction
3	mysql> rollback; Query OK, 0 rows affected (0.00 sec) mysql> select * from libros; +-----+------+--------------------------+------------+ | idl | ide | titulo | fecha | +-----+------+--------------------------+------------+ | 1 | 2 | Minería de Datos | 2017-11-01 | | 2 | 3 | Python 3 Curso Práctico | 2017-05-30 | | 3 | 3 | Unity 2017.X | 2017-10-01 | | 4 | 2 | Inteligencia Artificial | 2018-01-01 | | 5 | 2 | Aprender Raspberry Pi | 2017-01-01 | +-----+------+--------------------------+------------+ 5 rows in set (0.00 sec)
4		mysql> select * from libros; +-----+------+--------------------------+------------+ | idl | ide | titulo | fecha | +-----+------+--------------------------+------------+ | 1 | 2 | Minería de Datos | 2017-11-01 | | 2 | 3 | Python 3 Curso Práctico | 2017-05-30 | | 3 | 3 | Unity 2017.X | 2017-10-01 | | 4 | 2 | Inteligencia Artificial | 2018-01-01 | | 5 | 2 | Aprender Raspberry Pi | 2017-01-01 | +-----+------+--------------------------+------------+ 5 rows in set (0.00 sec)