oracle8.1.6
select user_id as student_name,
start_time, end_time
from lorsm_student_track
where community_id = :community_id
and course_id = :man_id
and end_time is not null
order by start_time desc
select user_id as student_name,
count(*) as counter, sum(end_time - start_time) as time_spent
from lorsm_student_track
where community_id = :community_id
and course_id = :man_id
and end_time is not null
group by user_id