CODEWITHSUNDEEP
phpmysqlsqljoinsubquery
user2666633
user2666633

Reputation: 340

How to write this complex SQL statement

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

Upvotes: 1

Views: 314

Answers (1)

Linger
Linger

Reputation: 15068

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

Upvotes: 1

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