Select MAX(ID) AS ID, FileSize FROM DupTable
GROUP BY FileSize
HAVING COUNT(*)=1
gives error: Circular reference cause by alias 'ID' in query definition's SELECT list
But the but the last SQL: Select * FROM DupTable WHERE FileSize in ( Select FileSize FROM DupTable GROUP BY FileSize HAVING COUNT(*)=1 ) is giving me the results I needed.
Thank You for the SQL and also teaching me about HAVING/WHERE