SQL error on duplicates

[Dan Rasch <drasch@xxxxxxxxxxxx>]

We have SQL in an RPG program that attempts to add a century code in
front of a date.  The date is part of the key.  But when the century 
code is added, on some records, it creates a duplicate key.  Most 
of the dates in the file are ok, but some have already had the century
code added, without deleting the original record. 

We get a duplicate key on this statement:

UPDATE XAMCNTP SET MCDTUP = MCDTUP + 1000000 
WHERE MCDTUP < 600000                        

This causes an CPF5009 error, and MONMSG does not ignore it.

Is there a way to handle dup keys with SQL?

TIA,

Dan Rasch - because if the human species concentrated on the really 
important things in life, there would be a shortage of fishing poles!
IBM Certified twice....... but still a couple PTFs away from Nirvana.