Horton

Re: cataloguing NOT NULL constraints

Alvaro Herrera <alvherre@alvh.no-ip.org>

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From: Alvaro Herrera <alvherre@alvh.no-ip.org>
To: Dean Rasheed <dean.a.rasheed@gmail.com>
Cc: Robert Haas <robertmhaas@gmail.com>, Peter Eisentraut <peter@eisentraut.org>, pgsql-hackers@lists.postgresql.org
Date: 2023-08-05T17:37:50Z
Lists: pgsql-hackers

Commits

Same data as JSON: GET /api/v1/messages/:b64id/commits the thread's linked commits as JSON, with link sources. API reference →

  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 2023-Aug-05, Dean Rasheed wrote:

> Hmm, thinking about this some more, I think this might be the wrong
> approach to fixing the original problem. I think it was probably OK
> that the NOT NULL constraint on the child was marked as inherited, but
> I think what should have happened is that dropping the PRIMARY KEY
> constraint on the parent should have caused the NOT NULL constraint on
> the child to have been deleted (in the same way as it would have been,
> if it had been a NOT NULL constraint on the parent).

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.

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.

-- 
Álvaro Herrera        Breisgau, Deutschland  —  https://www.EnterpriseDB.com/
"Nunca se desea ardientemente lo que solo se desea por razón" (F. Alexandre)