postgresql7.3
SELECT percent_score, to_char(creation_datetime, :format) AS session_start,
to_char(completed_datetime, :format) AS session_finish,
round(date_part('epoch', completed_datetime - creation_datetime)) as session_time
FROM as_sessions s
WHERE s.session_id = :session_id
select max(o.creation_date), s.session_id
from as_sessions s,
acs_objects o,
cr_revisions cr
where s.subject_id=:user_id
and s.assessment_id in (select revision_id from cr_revisions where item_id= :assessment_id)
and o.object_id = cr.item_id
and s.session_id = cr.revision_id
group by assessment_id, subject_id, session_id
limit 1