CODEWITHSUNDEEP
sqlunion
Floran Gmehlin
Floran Gmehlin

Reputation: 854

SQL UNION Query on the same table, same field

I'm trying to build a SQL Union Query which would return two columns (one per select) with the result from the same field, sorted with the WHERE clause.

Here is what I trying :

SELECT scg.grade AS course_1
FROM cp_StudentCourseGrade AS scg
JOIN cp_CourseSecSem AS css ON
css.courseSecSem_id = scg.courseSecSem_id
JOIN cp_Course AS c1 ON
c1.course_id = css.course_id
UNION
SELECT scg.grade AS course_2
FROM cp_StudentCourseGrade AS scg
JOIN cp_CourseSecSem AS css ON
css.courseSecSem_id = scg.courseSecSem_id
JOIN cp_Course AS c2 ON
c2.course_id = css.course_id**
WHERE c1.course_id = c2.course_id AND c1.course_id=1 AND c2.course_id=2;

and this should return me something like that : 

    course_1 | course_2
    -------------------
    4.0      | 6.0
    4.5      | 6.0
    6.0      | 5.5
    2.5      | 5.0
    1.0      | 4.0
    5.5      | 4.5

But I am having an error that says :

unknown column c1.course_id

Does anyone have an idea how I should do it?

Upvotes: 0

Views: 3442

Answers (2)

Laurence
Laurence

Reputation: 10976

If the grades are supposed to be linked to the same student, I'm going to guess something like this:

Select
  scg.student_id,
  Sum(Case When css.course_id = 1 Then scg.grade Else Null End) as course_1,
  Sum(Case When css.course_id = 2 Then scg.grade Else Null End) as course_2
From
  cp_StudentCourseGrade As scg
    Inner Join 
  cp_CourseSecSem As css 
    On css.courseSecSem_id = scg.courseSecSem_id
Group By
  scg.student_id

Upvotes: 1

cha
cha

Reputation: 10411

This is what you need:

SELECT scg1.grade AS course_1, scg2.grade AS course_2
FROM cp_StudentCourseGrade AS scg1
JOIN cp_CourseSecSem AS css1 ON
css1.courseSecSem_id = scg1.courseSecSem_id
JOIN cp_Course AS c1 ON
c1.course_id = css1.course_id AND c1.course_id=1 
JOIN cp_StudentCourseGrade AS scg2
JOIN cp_CourseSecSem AS css2 ON
css2.courseSecSem_id = scg2.courseSecSem_id
JOIN cp_Course AS c2 ON
c2.course_id = css2.course_id AND c2.course_id=2;

Upvotes: 1

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