SQL запрос - Общие вопросы и ошибки

$query = "SELECT prod.product_id, pr_cat.category_id FROM `khwld_jshopping_products` AS prod
                  INNER JOIN `khwld_jshopping_products_to_categories` AS pr_cat ON pr_cat.product_id = prod.product_id
                  LEFT JOIN `khwld_jshopping_categories` AS cat ON pr_cat.category_id = cat.category_id
                  WHERE prod.product_publish=1 AND cat.category_publish=1 AND cat.category_id = 38
                  GROUP BY prod.product_id DESC 
				  LIMIT 200;";