Thanks for the suggestion, but I knew that already.You could have told us that... ;)
The nulls first works on Oracle but not in other database servers so I'm reluctant to go that way.I don't think this is true. The NULL-handling is part of the ANSI:2003 extension of SQL. I agree that this extension is not implemented in all databases, but I'd adjust your statement to "but not in all other database servers".
Is there any way to tell Oracle to behave "nulls first" with some general preference I could activate for all the schema tables ?How would that not be Oracle-specific? Or do all other databases offer such a feature?