What's wrong in my query

Question

I wonder what is wrong with this query, it return too much rows (non unique values)

SELECT tt.*
FROM Arkusz1 tt
INNER JOIN
(
    SELECT ONTSERIALNUMBER, MAX(ONTBEUP) AS MaxBEUP
    FROM Arkusz1
    GROUP BY ONTSERIALNUMBER
) groupedtt 
    ON tt.ONTSERIALNUMBER = groupedtt.ONTSERIALNUMBER AND
       tt.ONTBEUP = groupedtt.MaxBEUP

despite the fact that subquery working correctly:

SELECT ONTSERIALNUMBER,
       MAX(ONTBEUP) AS MaxBEUP
FROM Arkusz1
GROUP BY ONTSERIALNUMBER

Answer 1

If your query is returning records which appear to be duplicate, it simply means that more than one record can correspond to a given serial number and maximum beup value. The quick fix here is to just use SELECT DISTINCT :

SELECT DISTINCT tt.*
FROM Arkusz1 tt
INNER JOIN
(
    SELECT ONTSERIALNUMBER, MAX(ONTBEUP) AS MaxBEUP
    FROM Arkusz1
    GROUP BY ONTSERIALNUMBER
) groupedtt 
    ON tt.ONTSERIALNUMBER = groupedtt.ONTSERIALNUMBER AND
       tt.ONTBEUP = groupedtt.MaxBEUP