如何寫這個複雜的SQL語句

Question

我有我的MySQL表即

first_term_result，second_term_result三個相同的表和third_term_result

這是列在它

exam_type_id | student_id | subject_id | mark | 

或示例帶有虛擬數據

注意：每個科目有三種不同的考試類型（CA1，CA2，CA3和考試）， 有三個這樣的表，它們具有相同的東西但數據不同，因爲它包含第一學期的數據，第二學期的數據和第三學期的最後一個數據。

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 | 

現在我想達到什麼是學生的名字讓每個學生WHERE subject_id = 7組的SUM()first_term_result.marksecond_term_result.mark和third_term_result.mark。

另一個非常重要的問題是，我將計算每個學生的first_term + second_term + third_term的總和，並且還希望能夠爲該學生和DESC中的主題訂購總計，以便我可以相應地定位它們請如果它會更容易在PHP請讓我知道。

感謝

在我看來很複雜，但我知道這裏有大師誰CA做到這一點，我讀的地方，可以通過甚至被用來彙總時訂購。

下面是我的代碼，顯然不工作。

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