Horton

Re: cataloguing NOT NULL constraints

Dean Rasheed <dean.a.rasheed@gmail.com>

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From: Dean Rasheed <dean.a.rasheed@gmail.com>
To: Alvaro Herrera <alvherre@alvh.no-ip.org>
Cc: Robert Haas <robertmhaas@gmail.com>, Peter Eisentraut <peter@eisentraut.org>, pgsql-hackers@lists.postgresql.org
Date: 2023-08-05T19:50:01Z
Lists: pgsql-hackers

Commits

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  1. Revert structural changes to not-null constraints

  2. Fix inconsistencies in error messages

  3. Disallow direct change of NO INHERIT of not-null constraints

  4. Disallow NO INHERIT not-null constraints on partitioned tables

  5. Better handle indirect constraint drops

  6. Don't try to assign smart names to constraints

  7. Fix restore of not-null constraints with inheritance

  8. ATTACH PARTITION: Don't match a PK with a UNIQUE constraint

  9. Fix propagating attnotnull in multiple inheritance

  10. Check stack depth in new recursive functions

  11. Move privilege check to the right place

  12. Update information_schema definition for not-null constraints

  13. Fix not-null constraint test

  14. Disallow changing NO INHERIT status of a not-null constraint

  15. Catalog not-null constraints

  16. parallel_schedule: add comment on event_trigger test dependency

  17. Revert "Catalog NOT NULL constraints" and fallout

  18. Adjust contrib/sepgsql regression test expected outputs.

  19. Fix table name clash in recently introduced test

  20. Catalog NOT NULL constraints

  21. Change the rules for inherited CHECK constraints to be essentially the same

On Sat, 5 Aug 2023 at 18:37, Alvaro Herrera <alvherre@alvh.no-ip.org> wrote:
>
> Yeah, something like that.  However, if the child had a NOT NULL
> constraint of its own, then it should not be deleted when the
> PK-on-parent is, but merely marked as no longer inherited.  (This is
> also what happens with a straight NOT NULL constraint.)  I think what
> this means is that at some point during the deletion of the PK we must
> remove the dependency link rather than letting it be followed.  I'm not
> yet sure how to do this.
>

I'm not sure that adding that new dependency was the right thing to
do. I think perhaps this could just be made to work using conislocal
and coninhcount to track whether the child constraint needs to be
deleted, or just updated.

> Anyway, I was at the same time fixing the other problem you reported
> with inheritance (namely, adding a PK ends up with the child column
> being marked NOT NULL but no corresponding constraint).
>
> At some point I wondered if the easy way out wouldn't be to give up on
> the idea that creating a PK causes the child columns to be marked
> not-nullable.  However, IIRC I decided against that because it breaks
> restoring of old dumps, so it wouldn't be acceptable.
>
> To make matters worse: pg_dump creates the PK as
>
>   ALTER TABLE ONLY parent ADD PRIMARY KEY ( ... )
>
> note the ONLY there.  It seems I'm forced to cause the PK to affect
> children even though ONLY is given.  This is undesirable but I don't see
> a way out of that.
>
> It is all a bit of a rat's nest.
>

I wonder if that could be made to work in the same way as inherited
CHECK constraints -- dump the child's inherited NOT NULL constraints,
and then manually update conislocal in pg_constraint.

Regards,
Dean