It occurred to me that we will also want to have NOT NULL NOT ENFORCED
constraints eventually. As we have discussed elsewhere, the NOT
ENFORCED state is closely related to the NOT VALID state. So that
should probably be considered in the design here.
Reading up on this again now, I'm confused about putting the NOT VALID
state for not-null constraints into pg_attribute. We have catalogued
not-null constraints now, so we can put metadata for them into
pg_constraint! And we have NOT VALID and NOT ENFORCED flags in
pg_constraint already.
So what is the purpose of the attnotnullvalid field? In the latest
posted patch, I don't see this column used in the executor for the
actual constraint checking. So is this all merely for clients to
understand the constraint metadata? If we add more metadata for
not-null constraints, do we need to add a new pg_attribute flag for each
one? That doesn't seem right.
