Sorry for the late reply, but thanks for your input, Jeff and Greg.
Greg, the trigger percent_two works for each statement. Would it be
possible to defer any check until the end of the transaction? For
example, I may need to insert into hundred values(1,25), followed by
(1,75), without the 25 immediately bombing.
Also is this solution safe for concurrent DML? I recently read an
Oracle solution to a similar problem in this blog entry's comments -
http://tkyte.blogspot.com/2007/03/dreaded-others-then-null-strikes-again.html
- and they said you need to lock before and after the validation.
Thanks,
Mark