SQL & PL/SQL

I have some STAMP columns in a table that I would like to populate with a trigger so that they are consistently populated.

On insert
STAMP_ADD_DATE
STAMP_ADDED_BY

On update
STAMP_UPDATE_DATE
STAMP_UPDATED BY

My problem is occuring on the update portion. Here is the text:
IF :new.stamp_updated_by IS NULL THEN
:new.stamp_updated_by := sys_context('USERENV', 'OS_USER');
END IF;
:new.stamp_update_date := d_today;

9 out of 10 times our .NET front end will pass in a value for :NEW.STAMP_UPDATED_BY to the procedure. That works great.

When I perform an update from SQL*Plus and omit the column from the update statement, it is reusing the :OLD.STAMP_UPDATED_BY value from the original record.

I would have expected it to realize that I have not referenced that column and fallen into the NULL condition in the trigger. Like a column default value..

Is there a way, without specifying the column name in the update statement to get this column to fall into the NULL condition if it is not specified in the update statement?


Thanks,
ds