Коэффициент эффективности/очистки в соединении нескольких подзапросов

Question

Я построил большой подзапрос и вам нужно отфильтровать и затем суммировать() его тремя разными способами. Я объединил его, а затем объединил эти агрегации, но это оставляет мне запрос с тремя идентичными разделами (подзапрос).

Есть ли более эффективный, программный или чистый способ достичь этого? Я понимаю, что чистые и эффективные могут быть совершенно разными.

Я выделил измененную часть каждого соединения.

select 
total_times.student_id 
, total_times.section_id 
, present_times.total as present 
, relation_times.total as relation 
, total_times.total as total 
from (
    select 
    s.student_id 
    , sec.section_id 
    , sum(sec_times.time) as total 
    from students s 
    join section_student_aff secsaff on secsaff.student_id = s.student_id 
    join sections sec on sec.section_id = secsaff.section_id 
    join (
     select distinct 
     site.site_id 
     , cal.date 
     , sec.section_id 
     , (time.end_time - time.start_time) as time 
     from calendar_days cal 
     join terms t on cal.date between t.start_date and t.end_date 
     join sessions ses on ses.session_id = t.session_id 
     join timeblocks blk on blk.session_id = ses.session_id 
     join timeblock_times time on time.timeblock_id = blk.timeblock_id 
     join sites site on site.site_id = ses.site_id 
     join section_timeblock_aff sectaff on sectaff.timeblock_id = blk.timeblock_id 
     join sections sec on sec.section_id = sectaff.section_id 
     where ses.academic_year = 2016 
     and time.day_of_week = extract(dow from cal.date) 
     order by site_id, date, section_id 
     ) sec_times 
     on sec_times.section_id = sec.section_id 

    --- Part 1 (no filter) --- 

    group by s.student_id, sec.section_id 
    ) total_times 
join (
    select 
    s.student_id 
    , sec.section_id 
    , sum(sec_times.time) as total 
    from students s 
    join section_student_aff secsaff on secsaff.student_id = s.student_id 
    join sections sec on sec.section_id = secsaff.section_id 
    join (
     select distinct 
     site.site_id 
     , cal.date 
     , sec.section_id 
     , (time.end_time - time.start_time) as time 
     from calendar_days cal 
     join terms t on cal.date between t.start_date and t.end_date 
     join sessions ses on ses.session_id = t.session_id 
     join timeblocks blk on blk.session_id = ses.session_id 
     join timeblock_times time on time.timeblock_id = blk.timeblock_id 
     join sites site on site.site_id = ses.site_id 
     join section_timeblock_aff sectaff on sectaff.timeblock_id = blk.timeblock_id 
     join sections sec on sec.section_id = sectaff.section_id 
     where ses.academic_year = 2016 
     and time.day_of_week = extract(dow from cal.date) 
     order by site_id, date, section_id 
     ) sec_times 
     on sec_times.section_id = sec.section_id 

    --- Part 2 --- 
    where exists (
     select null 
     from student_attendance sa 
     join attendance_flags af on af.attendance_flag_id = sa.attendance_flag_id 
     where 
     af.is_present=true 
     and sa.date = sec_times.date 
     and sa.sa_student_id = s.student_id 
     ) 
    -------------- 

    group by s.student_id, sec.section_id 
    ) present_times 
    on present_times.student_id = total_times.student_id 
    and present_times.section_id = total_times.section_id 
join (
    select 
    s.student_id 
    , sec.section_id 
    , sum(sec_times.time) as total 
    from students s 
    join section_student_aff secsaff on secsaff.student_id = s.student_id 
    join sections sec on sec.section_id = secsaff.section_id 
    join (
     select distinct 
     site.site_id 
     , cal.date 
     , sec.section_id 
     , (time.end_time - time.start_time) as time 
     from calendar_days cal 
     join terms t on cal.date between t.start_date and t.end_date 
     join sessions ses on ses.session_id = t.session_id 
     join timeblocks blk on blk.session_id = ses.session_id 
     join timeblock_times time on time.timeblock_id = blk.timeblock_id 
     join sites site on site.site_id = ses.site_id 
     join section_timeblock_aff sectaff on sectaff.timeblock_id = blk.timeblock_id 
     join sections sec on sec.section_id = sectaff.section_id 
     where ses.academic_year = 2016 
     and time.day_of_week = extract(dow from cal.date) 
     order by site_id, date, section_id 
     ) sec_times 
     on sec_times.section_id = sec.section_id 

    --- Part 3 --- 
    where sec_times.date between secsaff.entry_date and secsaff.leave_date 
    -------------- 

    group by s.student_id, sec.section_id 
    ) relation_times 
    on relation_times.student_id = total_times.student_id 
    and relation_times.section_id = total_times.section_id 
order by student_id, section_id 

Answer 1

Использование с, и условная сумма, она становится гораздо более управляемым (и, возможно, быстрее):

with 
    sec_times as (
    select distinct 
    site.site_id 
    , cal.date 
    , sec.section_id 
    , (time.end_time - time.start_time) as time 
    from calendar_days cal 
    join terms t on cal.date between t.start_date and t.end_date 
    join sessions ses on ses.session_id = t.session_id 
    join timeblocks blk on blk.session_id = ses.session_id 
    join timeblock_times time on time.timeblock_id = blk.timeblock_id 
    join sites site on site.site_id = ses.site_id 
    join section_timeblock_aff sectaff on sectaff.timeblock_id = blk.timeblock_id 
    join sections sec on sec.section_id = sectaff.section_id 
    where ses.academic_year = 2016 
    and time.day_of_week = extract(dow from cal.date) 
    ), 
    sec_times_full as (
    select 
    s.student_id 
    , sec.section_id 
    , sec_times.time 
    , exists (
     select null 
     from student_attendance sa 
     join attendance_flags af on af.attendance_flag_id = sa.attendance_flag_id 
     where 
     af.is_present=true 
     and sa.date = sec_times.date 
     and sa.sa_student_id = s.student_id 
     ) as is_present 
    , sec_times.date between secsaff.entry_date and secsaff.leave_date as is_relation 
    from students s 
    join section_student_aff secsaff on secsaff.student_id = s.student_id 
    join sections sec on sec.section_id = secsaff.section_id 
    join sec_times on sec_times.section_id = sec.section_id 
    ) 
select 
    student_id 
    , section_id 
    , sum(CASE WHEN is_present THEN time END) as present 
    , sum(CASE WHEN is_relation THEN time END) as relation 
    , sum(time) as total 
from sec_times_full 
group by student_id, section_id 
order by 1, 2