Finding duplicate rows in SQL

SELECT CONVERT(varchar,c.DayDate,3) AS DayDate, b.BlockName, tc.StudyYearID, tc.ClassName, a.StudentID, COUNT(a.StudentID) AS Occurrences
FROM tblAttendance a
INNER JOIN tblCalendar c ON c.DateID=a.DateID
INNER JOIN tblBlocks b ON b.BlockID=a.BlockID
INNER JOIN tblTimetableClass tc ON tc.ClassID=a.ClassID
GROUP BY c.DayDate, b.BlockName, tc.StudyYearID, tc.ClassName, a.StudentID
HAVING COUNT(a.StudentID)>1