T-SQL help to delete records

scover22
scover22 used Ask the Experts™
on
I need help coding a t-sql statement to delete certain records from a sql server table.  I'm including pictures of some data before the delete and after the delete. I'm currently doing the delete using VBA in Access 2010, but want to change to use a stored procedure.

This is what the data looks like before. The same studentID may have multiple records. I want to save the record with the largest SemesterPS and delete the others. If the student only has one records (eg: studentID = 45628), I do not want to delete that record.
data before desired delete
This is what the data should look like after the delete with one exception 35589 is not deleting the correct record.
how data should look after the delete
The delete statement I'm trying to use is
DELETE From DistanceBySemester WHERE SemesterPS Not In
(SELECT MAX(SemesterPS) from DistanceBySemester GROUP BY StudentID HAVING Count(*)>1)
But it is not deleting the records.

I tried using
DELETE From DistanceBySemester WHERE ID Not In
(SELECT MAX(SemesterPS) from DistanceBySemester GROUP BY StudentID HAVING Count(*)>1)
But that deleted all the records.

Thanks, Susan
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venk_r

Commented:
Try this.

DELETE

FROM DistanceBySemester T

INNER JOIN (

SELECT  MAX(SemesterPS) as MaxValue FROM DistanceBySemester GROUP BY StudentID
having count(*)>1

) A ON A.StudentID = T.StudentID

WHERE A.MaxValue <> T.SemesterPS
Top Expert 2010
Commented:
Try this:

SELECT StudentID, MAX(SemesterPS) AS SemesterPS
INTO #tmp
FROM DistanceBySemester
GROUP BY StudentID

DELETE FROM DistanceBySemester
FROM DistanceBySemester LEFT JOIN
    #tmp ON DistanceBySemester.StudentID = #tmp.StudentID AND 
        DistanceBySemester.SemesterPS = #tmp.SemesterPS
WHERE #tmp.SemesterPS IS NULL

DROP TABLE #tmp

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scover22

Author

Commented:
matthewspatrick's solution worked great the first time. I received a error when trying to running venk_r solution.  Thank you.
Anthony Perkins
Top Expert 2012

Commented:
Or simply in one query (no points please):
DELETE  d
FROM    DistanceBySemester d
        LEFT JOIN (SELECT   StudentID,
                            MAX(SemesterPS) LargestSemesterPS
                   FROM     DistanceBySemester
                   GROUP BY StudentID
                  ) x ON d.StudentID = x.StudentID
                         AND d.SemesterPS = x.LargestSemesterPS
WHERE   x.StudentID IS NULL

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Anthony Perkins
Top Expert 2012

Commented:
One point that you should consider is that if a StudentID should have the same SemesterPS which also happens to be the largest SemesterPS both will be returned.  If you want only one, then you will have to resort to a different solution.

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