HELP: SE 7.10.UD1 on SCO: AVG() in GROUP BY treats NULL as zero

I have an example of a query where the AVG() function as part of a GROUP BY clause treats NULLs as zeros. The problem appears only on larger datasets, although I have not (yet) spent hours establishing a minimal set. I have removed all unecessary clutter and established that removing the NULL values with a where clause will sidestep the problem. Unfortunately, this is not acceptable because I am trying to get the AVG of several columns. Is this a bug or am I going mad? Any help greatly appreciated. Incidentally, does SCO SE 7.10 have a reputation for bugginess? This is not the first serious problem I have found. -- Peter Lancashire Mail: Peter.Lancashire.PL1 at bayer.co.uk Information Systems Specialist, Bayer plc Eastern Way, Bury St Edmunds, Suffolk, IP32 7AH, UK Tel: +44-1635-562258, Fax: +44-1635-562281