Eliminating Duplicates in a Union situation

Question

Hi guys,
Just realized and stumbled upon a situation here and I need some help. I have a Query that gets all the departments and Students who took a survey by saying "Yes" or "No". Some of the Students could also be part of a "Board" and hold some special position.
Here is my UNION :
SELECT '"'||d.dept_type
       ||' - '||d.dept_code||'"'
       ||','||'"'||d.dept_desc||'"'
       ||','||'"'||0||'"'
from   department      d
group by d.dept_type, d.org_code, d.dept_desc
union
SELECT '"'||d.dept_type
       ||' - '||d.dept_code||'"'
       ||','||'"'||d.dept_desc||'"'
       ||','||'"'||COUNT(distinct(s.student_id))||'"'
from   student s,
         department d,
         survey sv
where  s.student_id = d.student_id
and      s.student_id = sv.student_id
and      sv.response = 'YES'
group by d.dept_type, d.org_code, d.dept_descBy doing this, I am being able to achieve departments that don't have any Students who said "Yes" in the survey but then again, when there is a department that did have a student that took the survey and said "Yes", I am getting two records.
Here is what the output is looking like :
"DEP - 01","Department 1","0"                                                                 
"DEP - 02","Department 2","0"                                                                                
"DEP - 02","Department 2","1"                                                                                
"DEP - 03","Department 3","0"                                                                                    
"DEP - 04","Department 4","0"                                                                     
"DEP - 04","Department 4","1"                                                                      As you can see, there are duplicates which I don't want. This is what the accurate result shoudl be like :
"DEP - 01","Department 1","0"                                                                 
"DEP - 02","Department 2","1"                                                                                
"DEP - 03","Department 3","0"                                                                                    
"DEP - 04","Department 4","1"                                                                      Any help would be awesome !

Answer 1

Hi,
As Toon suggested, this looks like an outer join problem, not a UNION.
If you did have to do a UNION, you could GROUP BY twice; once where you're doing it now, and again in the main query. Do the conversion to strings in the main query, only.
WITH     union_data     AS
     SELECT DISTINCT
               dept_type,   dept_code,   dept_desc,
            0                         AS sub_total
     FROM      department
UNION
     SELECT    d.dept_type, d.dept_code, d.dept_desc,
            COUNT (DISTINCT  s.student_id)     AS sub_total
     FROM      student         s,
                department       d,
                survey       sv
     WHERE         s.student_id       = d.student_id
     AND       s.student_id       = sv.student_id
     AND       sv.response       = 'YES'
     GROUP BY  d.dept_type, d.dept_code, d.dept_desc
SELECT       '"'     || dept_type          ||
       ' - '     || dept_code          ||
       '","'     || dept_desc          ||
       '","'     || SUM (sub_total)     ||
FROM       union_data
GROUP BY  dept_type,   dept_code,   dept_desc
;When you said org_code, did you mean dept_code?
Edited by: Frank Kulash on Aug 27, 2009 10:53 AM