SQL Query that summarizes students marks in a report card - sql

Question

Stupid simple question that I ended up spending 3.5 hours on. I'm running into a lot of syntax errors, so if anyone could help me answer this, I would learn a lot! Thank you so much!
I have 3 database tables:
Students Table
student_id, name
1, joe
2, jill
Courses Table
course_id, course_name
eng123, Engineering
stat111, Statistics
Marks Table
student_id, course_id, mark
1, stat111, 64
2, stat111, 90
1, eng123, 86
I need to write a single SQL query that will give me a summed up report card that looks like this:
student_id, student_name, eng123, stat 111
1, joe, 86, 64
2, jill, null, 90
---WHAT I EXPLORED:
I have looked into PIVOT, CASE and GROUP BY as my main leads, but I cannot put together the final pieces. My most promising query so far has been:
SELECT Students.student_id, Students.student_name,
CASE course_id WHEN 'eng123' THEN mark END as 'eng123',
CASE course_id WHEN 'stat111' THEN mark END as 'stat111'
FROM Students
INNER JOIN Marks
ON Students.student_id=Marks.student_id;
But that gives me the incorrect results of:
student_id, student_name, eng123, stat111
1, joe, null, 64
1, joe, 86, null
2, jill, null, 90

Answer 1

Your promising query is a stone's throw away from being what you want. You can simply modify it to GROUP BY the student_id and student_name (which should always pair the same together). Then take the sum of the marks. Note that I have added ELSE conditions to your CASE statements which assign a value of 0 (which therefore won't affect the sum aggregate).
SELECT Students.student_id, Students.student_name,
SUM(CASE course_id WHEN 'eng123' THEN mark ELSE 0 END) as 'eng123',
SUM(CASE course_id WHEN 'stat111' THEN mark ELSE 0 END) as 'stat111'
FROM Students
INNER JOIN Marks ON Students.student_id=Marks.student_id
GROUP BY Students.student_id, Students.student_name

Answer 2

Hi try using aggregate function MAX. try this:
WITH x AS (SELECT 1 AS student_id, 'joe' AS student_NAME FROM dual UNION ALL
SELECT 2 AS student_id, 'jill' AS student_NAME FROM dual),
y AS (SELECT 1 AS student_id , 'stat111' AS course_id, 64 AS mark FROM dual UNION ALL
SELECT 2 AS student_id , 'stat111' AS course_id, 90 AS mark FROM dual UNION ALL
SELECT 1 AS student_id , 'eng123' AS course_id, 86 AS mark FROM dual )
SELECT x.student_id, x.student_name,
MAX (CASE WHEN course_id = 'eng123' THEN mark END) eng123,
max(CASE WHEN course_id = 'stat111' THEN mark END) stat111
FROM x
INNER JOIN y
ON x.student_id=y.student_id
group by x.student_id, x.student_name;

Answer 3

select student_id,student_name,
max(case when course_id = 'eng123' then mark end) as eng123,
max(case when course_id = 'stat111' then mark end) as stat111
from (
SELECT Students.student_id as student_id,
Students.name as student_name,
Marks.course_id as course_id,
Marks.mark as mark
FROM Student Students
INNER JOIN Marks
ON Students.student_id=Marks.student_id)Z
group by student_id,student_name