syllabus.courses=courses.where("syllabus_id = #{syllabus.id}").select("courses.*,(SELECT MAX(updated_at) FROM `course_activities` WHERE course_activities.course_id = courses.id) AS updatetime").order("time desc")
syllabus.courses=courses.where("syllabus_id = #{syllabus.id}").select("courses.*,(SELECT MAX(updated_at) FROM `course_activities` WHERE course_activities.course_id = courses.id) AS updatetime").order("time desc")