sql 分组查询最新的数据

select o.* from (SELECT course_hour_id,max(create_time) as create_time FROM 
                 ol_course_hour_score GROUP BY course_hour_id) c 
                 left join ol_course_hour_score o on 
                 c.course_hour_id = o.course_hour_id and c.create_time = o.create_time