MS Access选择按多个字段分组的前n个查询

Question

This is part 2 of a problem that was already answered by peterm on this board. Thanks again peterm!

So I have code that will return the top 3 test scores for a given student. My table looks like the following:

StudentID, Test ID, Score
1,1, 95
1, 2, 90
1, 3, 90
1, 4, 90
2, 1, 99
2, 2, 95
2, 3, 90
2, 4, 90

Thanks to peterm, I have the following code which will do this for me:

SELECT StudentID, TestID, TestScore
  FROM MyTable t
 WHERE TestID IN
(
  SELECT TOP 3 TestID 
    FROM MyTable
   WHERE StudentID = t.StudentID 
   ORDER BY TestScore DESC, TestID
)
 ORDER BY StudentID, TestScore DESC, TestID;

My new problem is now I need to add two new fields to the table for Subject and Year, so I need to find the top 3 scores for each Subject-Student-Year combination. Once I have the top 3 scores for each combination, I need to average them so that I will have one averaged score of the top 3 scores for each student-subject-year combination. Hopefully, I've explained this clearly enough without having to mock up another table.

Thanks in advance.

Answer 1

You can do something like this

SELECT StudentID, Year, Subject,  AVG(TestScore) AS AvgScore
  FROM
(
  SELECT StudentID, Year, Subject, TestScore
   FROM MyTable t
   WHERE TestID IN
  (
   SELECT TOP 3 TestID 
     FROM MyTable
    WHERE StudentID = t.StudentID
      AND Year = t.Year
      AND Subject = t.Subject
    ORDER BY TestScore DESC, TestID
  )
) q
 GROUP BY StudentID, Year, Subject
 ORDER BY StudentID, Year, Subject;

Sample output:

| STUDENTID | YEAR | SUBJECT | AVGSCORE |
|-----------|------|---------|----------|
|         1 | 2012 |       1 |       91 |
|         1 | 2012 |       2 |       84 |
|         2 | 2012 |       1 |       94 |
|         2 | 2012 |       3 |       95 |

Here is SQLFiddle demo.
Demo as usually is for SQL Server but expected to work in MS Access, maybe with minor syntactic tweaks