Question

I’ve created a view that contains:

 student_full_name    subject_code    result
 Jennifer Higgins     CS1234          81
 Jennifer Higgins     CS1235          90
 Kal Penn             CS1234          70
 Kal Penn             CS1235          60
 Han Solo             CS1234          45
 Han Solo             CS1235          70

I am trying to get:

1. Average result of each student so like say Jennifer Higgins enrolled in CS1234 and CS1235.
   Her average mark would be 85.50.

2. Then Jennifer Higgins marks would be compared to the average mark of all enrolments
   So totalling up the AVG(result) for all subjects.

3. The query would then list all the students who are getting above average scores.

I know I have to use a sub query here in order to get the AVG of all results.
Well this is sort of a pseudo code. I am quite stuck as I’m not sure how to make the subquery compare itself to the query’s results.
I’m pretty sure I need two group by statements one for the grouping by student_full_name and the other to get all of the average results.

 SELECT student_full_name,
        AVG(results) AS average_result
 FROM viewEnrol
 WHERE average_result > ( SELECT (AVG(results))
                          FROM viewEnrol

 GROUP BY student_full_name

//EDIT

OUTPUT should look like. Kal Penn and Han Solo is not listed as they didn’t get above average mark.
Average mark of all subjects is 69.33. Han Solo got 57.5 and Kal Penn got 65.

 student_full_name    subject_code    result
 Jennifer Higgins     CS1234          85.5

Any help?

Answer 1

This should do the job. First inner query will give you the result of average of all students.
While second will give the avg for the table.

    SELECT student_full_name 
    FROM (SELECT student_full_name,
                 AVG(results) AS average_Sresult
          FROM viewEnrol
          GROUP BY student_full_name) sre, 
         (SELECT (AVG(results)) tavg
          FROM viewEnrol) ta
     WHERE sre.average_Sresult > ta.tavg

PS: Should not you take the avg of avg rather than taking the avg of all results.