Re: [HACKERS] pg_upgrade failed with error - ERROR: column "a" in child table must be marked NOT NULL

Michael Paquier <michael.paquier@gmail.com> writes:
> The documentation says the following:
> https://www.postgresql.org/docs/9.3/static/ddl-inherit.html
> All check constraints and not-null constraints on a parent table are
> automatically inherited by its children. Other types of constraints
> (unique, primary key, and foreign key constraints) are not inherited.

> When adding a primary key, the system does first SET NOT NULL on each
> column under cover, but this does not get spread to the child tables
> as this is a PRIMARY KEY. The question is, do we want to spread the
> NOT NULL constraint created by the PRIMARY KEY command to the child
> tables, or not?

Yeah, I think we really ought to for consistency.  Quite aside from
pg_dump hazards, this allows situations where selecting from an
apparently not-null column can produce nulls (coming from unconstrained
child tables).  That's exactly what the automatic inheritance rules
are intended to prevent.  If we had a way to mark NOT NULL constraints
as not-inherited, it'd be legitimate for ADD PRIMARY KEY to paste on
one of those instead of a regular one ... but we lack that feature,
so it's moot.

Not sure what's involved there code-wise, though, nor whether we'd want
to back-patch.
        regards, tom lane