Question

I’m having trouble wrapping my mind around developing this SQL query. Given the following two tables:

• ACADEMIC_HISTORY ( STUDENT_ID, TERM, COURSE_ID, COURSE_GRADE )
• COURSE_EQUIVALENCIES ( COURSE_ID, COURSE_ID_EQUIVALENT )

What would be the best way to detect if students have taken the same (or an equivalent) course in the past with a passing grade (C or better)?

Example

Student #1 took the course ABC001 and received a grade of C. Ten years later, the course was renamed ABC011 and the appropriate entry was made in COURSE_EQUIVALENCIES. The student retook the course under this new name and received a grade of B. How can I construct a SQL query that will detect the duplicate courses and only count the first passing grade?

(The actual case is significantly more complicated, but this should get me started.)

Thanks in advance.

EDIT:
It’s not even necessary to keep or discard any information. A query that simply shows classes with duplicates will be sufficient.

Answer 1

you could use something like:

SELECT 
    STUDENT_ID
    ,MIN (COURSE_GRADE)
FROM (
    SELECT * FROM         
        ACADEMIC_HISTORY 
    WHERE COURSE_ID =1

    UNION

    SELECT 
        h.STUDENT_ID
        ,h2.COURSE_ID
        ,h2.COURSE_GRADE
    FROM
    ACADEMIC_HISTORY AS h
    LEFT OUTER JOIN COURSE_EQUIVELANCIES as e
        ON e.COURSE_ID = h.COURSE_ID
    LEFT OUTER JOIN ACADEMIC_HISTORY as h2
        ON h.STUDENT_ID = h2.STUDENT_ID
        AND h2.COURSE_ID = e.COURSE_ID_EQUIVELANT
    WHERE
         h.COURSE_ID =1
) AS t
WHERE STUDENT_ID =1
GROUP BY STUDENT_ID

http://sqlfiddle.com/#!3/d608f/20

Sorry posted with a bug.. it preferred the score of the actual course requested over any equivalencies – fixed now

this only looks for one level of equivalencies.. but maybe you want to enforce that and have that part of the data entry process.. review all possible equivalencies and enter the valid ones

EDIT: for first pass of qualifying course (using numbered terms..)

SELECT TOP 1
    STUDENT_ID
    ,MIN (COURSE_GRADE)
FROM (
    SELECT * FROM         
        ACADEMIC_HISTORY 
    WHERE COURSE_ID =1

    UNION

    SELECT 
        h.STUDENT_ID
        ,h2.COURSE_ID
        ,h2.TERM
        ,h2.COURSE_GRADE
    FROM
    ACADEMIC_HISTORY AS h
    LEFT OUTER JOIN COURSE_EQUIVELANCIES as e
        ON e.COURSE_ID = h.COURSE_ID
    LEFT OUTER JOIN ACADEMIC_HISTORY as h2
        ON h.STUDENT_ID = h2.STUDENT_ID
        AND h2.COURSE_ID = e.COURSE_ID_EQUIVELANT
    WHERE
         h.COURSE_ID =1
) AS t
WHERE STUDENT_ID =1

GROUP BY STUDENT_ID, TERM
ORDER BY TERM ASC

http://sqlfiddle.com/#!3/fdded/6

(note TOP is a t-sql command for MySQL you need LIMIT)