Datepart i select

Denne query virker i SQL, men i access brokker den sig over at denne query er for kompleks ...?

Hvordan får jeg lige access til at forstå denne ?

SELECT    DATEPART(mm, LetterDate) AS M, DATEPART(yy, LetterDate) AS Y, COUNT(LetterID) AS Antal
FROM        _tblLetter
WHERE    (LetterReplied = 1)
GROUP BY DATEPART(mm, LetterDate), DATEPART(yy, LetterDate)
ORDER BY DATEPART(yy, LetterDate), DATEPART(mm, LetterDate)