Re: Prevent ALTER TABLE DROP NOT NULL on child tables if parent column has it

Michael Paquier <michael(dot)paquier(at)gmail(dot)com> writes:
> On Wed, Jun 15, 2016 at 10:34 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>> My feeling is that we'd keep
>> the pg_attribute.attnotnull field and continue to drive actual enforcement
>> off that, but it would just reflect a summary of the pg_constraint state.

> OK, I see. Hm, by storing this information I would actually think that
> we want to drop this attnotnull so as we don't need to bother about
> updating pg_attribute through the whole tree when dropping a NOT NULL
> constraint on the parent, and we do not actually need to store this
> information in two different places..

There are a couple of reasons for not removing attnotnull: one is to not
need to touch the executor for this, and another is to not break
client-side code that is accustomed to looking at attnotnull.

regards, tom lane