SQL cursor & stored procedure order arrangement - mysql

Question

I was working on a stored procedure to update the order field in a product table.
It works only the problem now is the the last item in the loop(cur), is increased twice instead of once (so dubbeled). Like so:
+-----------------+
|product + order |
|_id | |
| | |
| 1 | 0 |
| 2 | 1 |
| etc.. | etc..|
| 36 | 35 |
| 37 | 36 |
| 38 | 38 |
| |
+-----------------+
I cant figure out why. The link table(CategoryProduct) in this case goes to 38 with a category_id of 2 CALL curorder(2);
Stored procedure:
DELIMITER //
CREATE PROCEDURE curorder(
IN catid INT
)
BEGIN
DECLARE done INT DEFAULT FALSE;
DECLARE i INT DEFAULT 0;
DECLARE p INT;
DECLARE cur CURSOR FOR SELECT product_id FROM test.CategoryProduct WHERE category_id = catid;
DECLARE CONTINUE HANDLER FOR NOT FOUND SET done = TRUE;
OPEN cur;
read_loop: LOOP
FETCH cur INTO p;
UPDATE `test`.`Product` SET `order` = i WHERE `Product`.`product_id` =p;
SET i = i + 1;
IF done THEN
LEAVE read_loop;
END IF;
END LOOP;
CLOSE cur;
END //
DELIMITER ;
The Database is a Mysql Database. Any suggestions for improving the procedure are always welcome.
Thanks in advance.
EDIT:
I already tried to place the SET i STATEMENT beneath the IF STATEMENT but with no result.

Answer 1

You should put:
IF done THEN
LEAVE read_loop;
END IF;
Above your update statement, the last time mysql walks trough the loop is uses the old variables because there is no new 'p'. but i is incremented.
I good way to debug stored procedures is with a log table:
CREATE TABLE procedureLog
(
id INTEGER AUTO_INCREMENT,
description TEXT,
PRIMARY KEY (id)
);
For this case you can log the update parameters with the follow query:
INSERT INTO  `test`.`procedureLog` (`id` ,`description`) VALUES (null,  CONCAT('id: ', CAST(p as CHAR), ' order: ', CAST(i as CHAR)));
Good luck!