Selecting better query from performance point of view.

Question

Hi friends,
I have one situation which following example represents exactly.
we have a table marks.
Table Marks ( Student_No number,exam_code number, Mark_subject1 number, Mark_subject2 number, Mark_subject3 number).
What I want is to prepare a table Results in following way.
I need to insert one record for each student's each total Marks of each subject.
Like
Marks:
Student_No...........Exam_code........Mark_subject1........Mark_subject2........Mark_subject3
.........1.......................1.....................10.........................15..........................12
.........1.......................2.....................15.........................15..........................10
.........2.......................1.....................10.........................10..........................10
.........2.......................2.....................17.........................17..........................10
Then I want to populate results table with following data.
Student...................Subject..............TotalMarks
.....1.......................Subject1..................25
.....1.......................Subject2..................30
.....1.......................Subject3..................22
.....2.......................Subject1..................27
.....2.......................Subject2..................27
.....2.......................Subject3..................20
This needs to be done within one procedure.
I can do it by two ways.
1)
insert into Results select student_no, 'Subject1',sum(Mark_Subject1) from marks group by student_no;
insert into Results select student_no,'Subject2',sum(Mark_Subject2) from Marks group by student_no;
insert into Results select student_no,'Subject2',sum(Mark_Subject3) from Marks group by student_no;
2)
For i in (select student_no,sum(mark_subject1) sub1, sum(mark_subject2) sub2, sum(mark_subject3) sub3 from marks)
loop
insert into Results values(i.student_no,'Subject1',i.sub1);
insert into Results values(i.student_no,'Subject2',i.sub2);
insert into Results values(i.student_no,'Subject3',i.sub3);
end loop;
If we use first way, 3 times the table will be accessed and will be processed (sorted) for "grouped by" and all the resultant data will be inserted.
If we use second way, the marks table will be accessed and processed for group by for only once. But for each record of result set, 3 inserts will be done.
I am confused about which would be better way provided the number of records in marks table is around 1,00,000.
Please help me deciding the better way.
Regards,
Dipali..

Answer 1

I would avoid cursor for loops if at all possible.