Is there any overhead associated with NOT NULL? I ask because all my
inserts and updates are controlled by an application layer -- most
pre-update or pre-insert validation is done there as it is more flexible
for my situation. I know it's a good idea to specify NOT NULL when
appropriate, if for no other reason than to have a self-documenting
schema -- however, I am wondering what the expense of such a constraint
is.

TIA,

Robert