SQL - Find duplicates with equivalencies - sql

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)

Answer 2

The data (in LOWERCASE)
DROP SCHEMA tmp CASCADE;
CREATE SCHEMA tmp;
SET search_path='tmp';
CREATE TABLE academic_history
( student_id INTEGER NOT NULL
, course_id CHAR(6)
, course_grade CHAR(1)
, PRIMARY KEY(student_id,course_id)
);
INSERT INTO academic_history ( student_id,course_id,course_grade) VALUES
(1, 'ABC001' , 'C' )
, (1, 'ABC011' , 'B' )
, (2, 'ABC011' , 'A' )
;
CREATE TABLE course_equivalencies
( course_id CHAR(6)
, course_id_equivalent CHAR(6)
);
INSERT INTO course_equivalencies(course_id,course_id_equivalent) VALUES
( 'ABC011' , 'ABC001' )
;
The query:
-- EXPLAIN ANALYZE
WITH canon AS (
SELECT ah.student_id AS student_id
, ah.course_id AS course_id
, COALESCE (eq.course_id_equivalent,ah.course_id) AS course_id_equivalent
FROM academic_history ah
LEFT JOIN course_equivalencies eq ON eq.course_id = ah.course_id
)
SELECT h.student_id
, c.course_id_equivalent
, MIN(h.course_grade) AS the_grade
FROM academic_history h
JOIN canon c ON c.student_id = h.student_id AND c.course_id = h.course_id
GROUP BY h.student_id, c.course_id_equivalent
ORDER BY h.student_id, c.course_id_equivalent
;
The output:
NOTICE: drop cascades to 2 other objects
DETAIL: drop cascades to table tmp.academic_history
drop cascades to table tmp.course_equivalencies
DROP SCHEMA
CREATE SCHEMA
SET
NOTICE: CREATE TABLE / PRIMARY KEY will create implicit index "academic_history_pkey" for table "academic_history"
CREATE TABLE
INSERT 0 3
CREATE TABLE
INSERT 0 1
student_id | course_id_equivalent | the_grade
------------+----------------------+-----------
1 | ABC001 | B
2 | ABC001 | A
(2 rows)