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mysql> select `stock` from `test_shop_item` limit 10;
+-------+
| stock |
+-------+
|    18 |
|    10 |
|     2 |
|     2 |
|     3 |
|     3 |
|     7 |
|     8 |
|     4 |
|     5 |
+-------+
10 rows in set (0.00 sec)

mysql> SET autocommit=0;
Query OK, 0 rows affected (0.00 sec)

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

mysql> UPDATE `test_shop_item` SET `stock` = `stock` * 2;
Query OK, 650 rows affected (0.07 sec)
Rows matched: 848  Changed: 650  Warnings: 0

mysql> select `stock` from `test_shop_item` limit 10;
+-------+
| stock |
+-------+
|    36 |
|    20 |
|     4 |
|     4 |
|     6 |
|     6 |
|    14 |
|    16 |
|     8 |
|    10 |
+-------+
10 rows in set (0.00 sec)

mysql> ROLLBACK;
Query OK, 0 rows affected, 1 warning (0.00 sec)

mysql> select `stock` from `test_shop_item` limit 10;
+-------+
| stock |
+-------+
|    36 |
|    20 |
|     4 |
|     4 |
|     6 |
|     6 |
|    14 |
|    16 |
|     8 |
|    10 |
+-------+
10 rows in set (0.00 sec)