Tks vbaInet! It looks as if this could be the solution.
Unfortunately, I get "Data type mismatch in criteria expression" error message.
SELECT DISTINCTROW Partition([NazivFirme], 0, 50, 5) AS Range,
Count(Klijenti.NazivFirme) AS [Count]
FROM Klijenti
GROUP BY Partition([NazivFirme], 0, 50...