Getting the above average student from database

Question

I\'ve created a view that contains:

 student_full_name    subject_code    result
 Jennifer Higgins     CS1234          81
 Jennifer Higgins     CS1235                


        

Answer 1

If you want to filter your results after aggregation (like avg), you need to use having rather than where.

General rule is:

• where filters what raw (non-aggregated) rows you get from the actual database before the aggregation takes place; and
• having filters what (possibly aggregated) rows are finally delivered to you.

Something like (though untested):

SELECT   student_full_name,
         AVG (results) AS average_result
FROM     viewEnrol
GROUP BY student_full_name
HAVING   AVG (results) > ( SELECT AVG (results) FROM viewEnrol )