#-- This whole file was just an attempt to rebuild queries because I was getting duplicate entries for 
the queries, both in the admin php and the servlet code, for the display of scheduled presentations. Turned out
it was really because there were duplicate entries (i.e. records with the same user id) in the user table.

#This works, but duplication has already appeared
select spkr_name, pre_date, ses_period, ses_start
from speaker, presentation, session
where pre_spkr_id = spkr_u_id
and pre_ses_id = ses_id
and pre_scl_id = ses_scl_id
order by pre_date

#-- this works with no duplication,but doesn't get speaker name:
 select  pre_date, pre_spkr_id, ses_period, ses_start 
 from  presentation, session
 where  pre_ses_id = ses_id and pre_scl_id = ses_scl_id 
 order by pre_date;

#... adding teacher name:
select spkr_name, pre_date, ses_start, tchr_name
from speaker, presentation, session, teacher
where pre_spkr_id = spkr_u_id
and pre_ses_id = ses_id
and pre_scl_id = ses_scl_id
and pre_tchr_id = tchr_u_id

#.. adding room and subject: this is where the duplication occurs
# if I use "select distinct" it works fine.
select  spkr_name, pre_date, ses_start, tchr_name, tp_subject, tp_room
from speaker, presentation, session, teacher, teacherperiod
where pre_spkr_id = spkr_u_id
and pre_ses_id = ses_id
and pre_scl_id = ses_scl_id
and pre_tchr_id = tchr_u_id
and pre_tchr_id = tp_tchr_id
and ses_period = tp_period 
order by pre_date
;

#attempt at simple duplication: presentation, session, and tp_period This produces a huge long list.
select pre_date, ses_start, tp_subject, tp_room
from presentation, session, teacherperiod
where pre_ses_id = ses_id
and pre_ses_id = ses_id
and pre_scl_id = ses_scl_id
and ses_period = tp_period
order by pre_date
;