trigger not working on same database on two versions of mysql

[Liviu Vasut]

Hello,
I have a table which stores quantities of items and I needed a way to prevent clients to enter negative values. So I added a trigger to trow an error. On my development station (mysql 5.1.52 Source distribution) it works on both insert and update. On the production server (mysql 5.0.88-log Source distribution) it only works for inserts.

table definition:
CREATE TABLE `goods` (
`id` int(8) unsigned NOT NULL AUTO_INCREMENT,
...other fields...
`quantity` int(7) NOT NULL DEFAULT '0',
PRIMARY KEY (`id`),
...other keys and constraints...
) ENGINE=InnoDB;

trigger definition:
DELIMITER |
CREATE TRIGGER `negative_insert`
BEFORE INSERT ON `goods`
FOR EACH ROW BEGIN
IF NEW.`quantity` < 0 THEN
SET NEW.`quantity` = 1 / 0;
END IF;
END;
|
CREATE TRIGGER `negative_update`
BEFORE UPDATE ON `goods`
FOR EACH ROW BEGIN
IF NEW.`quantity` < 0 THEN
SET NEW.`quantity` = 1 / 0;
END IF;
END;
|
DELIMITER ;

for testing I did:
(development station)
mysql> INSERT INTO goods (quantity) values (-1);
ERROR 1048 (23000): Column 'quantity' cannot be null
mysql> update goods set quantity =-1 where id=1;
ERROR 1048 (23000): Column 'quantity' cannot be null

(production server)
mysql> INSERT INTO goods (quantity) values (-1);
ERROR 1048 (23000): Column 'quantity' cannot be null
mysql> update goods set quantity =-1 where id=1;
Query OK, 0 rows affected, 1 warning (0.00 sec)
Rows matched: 1 Changed: 0 Warnings: 1
mysql> show warnings;
+---------+------+--------------------------------+
| Level | Code | Message |
+---------+------+--------------------------------+
| Warning | 1048 | Column 'quantity' cannot be null |
+---------+------+--------------------------------+
1 row in set (0.00 sec)

As you can see it only generates a warning. How can I change it into an error?
Thank you for your time.