How to write this complex SQL statement - php

Question

I have three identical tables in my MySQL table namely
first_term_result, second_term_result and third_term_result
this are the columns in it
exam_type_id | student_id | subject_id | mark |
or example with dummy data
NOTE: there are three different exam type for each subjects (CA1, CA2, CA3 and Exam),
there are three table like this with same thing but different data as it hold data for first term another for second term and the last for third term.
first_term_result:
exam_type_id | student_id | subject_id | mark |
1 | 6 | 7 | 12 |
2 | 6 | 7 | 9 |
3 | 6 | 7 | 13 |
4 | 6 | 7 | 45 |
1 | 4 | 7 | 7 |
2 | 4 | 7 | 5 |
3 | 4 | 7 | 10 |
4 | 4 | 7 | 34 |
second_term_result:
exam_type_id | student_id | subject_id | mark |
1 | 6 | 7 | 15 |
2 | 6 | 7 | 6 |
3 | 6 | 7 | 10 |
4 | 6 | 7 | 50 |
1 | 4 | 7 | 6 |
2 | 4 | 7 | 3 |
3 | 4 | 7 | 9 |
4 | 4 | 7 | 44 |
third_term_result:
exam_type_id | student_id | subject_id | mark |
1 | 6 | 7 | 17 |
2 | 6 | 7 | 8 |
3 | 6 | 7 | 15 |
4 | 6 | 7 | 67 |
1 | 4 | 7 | 12 |
2 | 4 | 7 | 8 |
3 | 4 | 7 | 12 |
4 | 4 | 7 | 50 |
Now what i want to achieve is get the SUM() of first_term_result.mark second_term_result.mark and third_term_result.mark of each students WHERE subject_id=7 group by students name.
another very important problem is i will be calculating the grand sum for each students for first_term+second_term+third_term and also want to be able to order the grand total for that student and the subjects in DESC so i can position them accordingly please if it will be easier on php please let me know.
Thanks
it seems very complex to me but i know there are gurus here who ca achieve this, i read somewhere that it is possible to order by even when rollup is used.
below is my code which doesn't work obviously.
SELECT CONCAT(s.fname,' ',s.mname,' ',s.lname) AS sname,
SUM(f.mark) AS first_total,
SUM(se.mark) AS second_total,
SUM(t.mark) AS third_total
SUM(f.first_total,second.total,third_total) as GT // just to show my intention
FROM students s, first_term_result f, second_term_result se, third_term_result t
WHERE s.studentID=f.student_id AND
s.studentID=se.student_id AND
s.studentID=t.student_id AND
f.subject_id=7 AND
se.subject_id=7 AND
t.subject_id=7
GROUP BY sname ORDER BY GT DESC

Answer 1

SELECT CONCAT(MS.fname,' ',MS.mname,' ',MS.lname) AS sname,
M.FTotal, M.STotal, M.TTotal,
(M.FTotal + M.STotal + M.TTotal) AS GrandTotal
FROM (
SELECT st.studentID,
(
SELECT SUM(f.mark)
FROM first_term_result AS f
WHERE f.subject_id = 7
AND f.student_id = st.studentID
) AS FTotal,
(
SELECT SUM(s.mark)
FROM second_term_result AS s
WHERE s.subject_id = 7
AND s.student_id = st.studentID
) AS STotal,
(
SELECT SUM(t.mark)
FROM third_term_result AS t
WHERE t.subject_id = 7
AND t.student_id = st.studentID
) AS TTotal
FROM students AS st
WHERE st.studentID IN (
SELECT studentID
FROM first_term_result AS fs
WHERE fs.subject_id = 7
AND fs.student_id = st.studentID)
GROUP BY st.studentID
) AS M
JOIN students MS ON M.studentID = MS.studentID
ORDER BY (M.FTotal + M.STotal + M.TTotal) DESC