1、进入课程资源库，对资源进行排序 2、先点击“大小”排序，再点击“文件”排序 3、报错 Mysql2::Error: Unknown column 'size' in 'order clause': SELECT DISTINCT `courses`.id FROM `courses` LEFT OUTER JOIN `attachments` ON `attachments`.`container_id` = `courses`.`id` AND `attachments`.`container_type` = 'Course' WHERE `courses`.`id` = 68 ORDER BY attachments.filename,size desc LIMIT 1