Union? Intersect? Or inversed intersect?

Question

I'm working on a select statement that should return the class for each of the school days. There are 4 school days before the cycle starts over again. (e.g. Monday = Day1, Tuesday = Day2...Thursday = Day4, Friday = Day1..etc )

Some students may have 1 period off on certain days, in which case we should display an empty space on that day/period combination.

At the moment, the select statement only returns days which have a value.

Example:

            Day 1    Day 2    Day 3    Day 4
Period 1    class    class    off      class
Period 2    class    class    class    off
Period 3    off      class    class    class
Period 4    class    off      class    class

What I'm trying to accomplish is to have the select statement return an empty row (with null values) in place of the period that is off on a certain day. I tried adding Unions with the day as the only value.

This isn't working as I'm getting my first 3 rows and then the 4 others, but what I actually want is the first 3 rows (e.g. with the days 1,3,4) and the last union'ed row (e.g. day 2) in which case I can then afterwards do an order by on the day.

How can I do this? Should I be using an intersect? ..or the opposite of an intersect? Also this is for an Oracle database.

Select statement:

select spct.course_code||'-'||spct.course_section as course,t.school_cycle_day as jour,p.legal_first_name,p.legal_surname,sc.room_no
from   student_program_class_tracks@trl spct,class_meetings@trl cm,school_classes@trl sc,persons@trl p,timeslots@trl t,school_timeline_periods@trl tsp
where  spct.school_code=cm.school_code
and    spct.school_code=sc.school_code
and    spct.school_code=t.school_code
and    spct.school_code=tsp.school_code
and    spct.school_year=cm.school_year
and    spct.school_year=sc.school_year
and    spct.school_year=t.school_year
and    spct.school_year=tsp.school_year
and    t.school_year_track=tsp.school_year_track
and    t.school_timeline_code=tsp.school_timeline_code
and    t.school_period=tsp.school_period
and    spct.class_code=cm.class_code
and    spct.class_code=sc.class_code
and    sc.reporting_teacher=p.person_id
and    cm.block=t.block
and    spct.school_code='73'
and    spct.school_year='20122013'
and    spct.person_id='000170629'
and    cm.semester='2'
and    cm.term='1'
and    t.school_period='1'
and    ((spct.start_date <= sysdate and spct.end_date >= sysdate) or spct.demit_indicator='0')
--order by t.school_cycle_day

UNION

SELECT '','1','','','' from DUAL

UNION

SELECT '','2','','','' from DUAL

UNION

SELECT '','3','','','' from DUAL

UNION

SELECT '','4','','','' from DUAL;

Output:

Course         Jour    Legal_first_name   Legqal_surname     Room_no
PPL4OO-03      2       François           Belle-Isle     1-139
SBI4UU-02      4       Louise             Bérubé             1-155
TFC4EE-02      3       Gino               Proulx             1-127
           1            

Thanks for any help you can provide!

Answer 1

If what you are saying is that you want 4 rows per pupil then something like the following should do it.

SELECT
    B.course
    A.school_cycle_day,
    B.legal_first_name,
    B.legal_surname,
    B.room_no
FROM
    (
        SELECT '1' AS school_cycle_day
        FROM DUAL

        UNION ALL

        SELECT '2'
        FROM DUAL

        UNION ALL

        SELECT '3'
        FROM DUAL

        UNION ALL

        SELECT '4'
        FROM DUAL
    ) A
    LEFT JOIN
   (
      select
           spct.course_code||'-'||spct.course_section as course,
           t.school_cycle_day as jour,
           p.legal_first_name,
           p.legal_surname,
           sc.room_no
      from
           student_program_class_tracks@trl spct,
           class_meetings@trl cm,
           school_classes@trl sc,
           persons@trl p,
           timeslots@trl t,
           school_timeline_periods@trl tsp
      where
           spct.school_code=cm.school_code and
           spct.school_code=sc.school_code and
           spct.school_code=t.school_code and
           spct.school_code=tsp.school_code and
           spct.school_year=cm.school_year and
           spct.school_year=sc.school_year and
           spct.school_year=t.school_year and
           spct.school_year=tsp.school_year and
           t.school_year_track=tsp.school_year_track and
           t.school_timeline_code=tsp.school_timeline_code and
           t.school_period=tsp.school_period and
           spct.class_code=cm.class_code and
           spct.class_code=sc.class_code and
           sc.reporting_teacher=p.person_id and
           cm.block=t.block and
           spct.school_code='73' and
           spct.school_year='20122013' and
           spct.person_id='000170629' and
           cm.semester='2' and
           cm.term='1' and
           t.school_period='1' and
           ((spct.start_date <= sysdate and spct.end_date >= sysdate) or  spct.demit_indicator='0')
) B ON A.school_cycle_day = B.school_cycle_day