Re: CHECK Constraint Deferrable

On Tue, Oct 3, 2023 at 10:05 AM David G. Johnston
<david(dot)g(dot)johnston(at)gmail(dot)com> wrote:
>> The real-world use case, at least for me, is when using an ORM. For large object-graphs ORMs have a tendency to INSERT first with NULLs then UPDATE the “NOT NULLs” later.
>>
>> “Rewrite the ORM” is not an option for most of us…
>
> Between this and Vik comment it sounds like we should probably require a patch in this area to solve both the not null and check constraint deferral omissions then, not just one of them (alternatively, let’s solve the not null one first).

I have a couple of problems with this comment:

1. I don't know which of Vik's comments you're talking about here, but
it seems to me that Vik is generally in favor of this feature, so I'm
a bit surprised to hear that one of his comments led you to think that
it should be burdened with additional requirements.

2. I don't think it's a good idea for the same patch to try to solve
two problems unless they are so closely related that solving one
without solving the other is not sensible. It is a good policy for the
community to accept incremental progress provided it doesn't break
things along the way. Smaller patches are way easier to get committed,
and then we get some of the feature sooner instead of all of it some
more distant point in the future or never. Furthemore, forcing
additional requirements onto patch submitters as a condition of patch
acceptance is extremely demoralizing to submitters, and we should not
do it without an excellent reason.

Mind you, I'm not against this patch handling both CHECK and NOT NULL
constraints if that's the most sensible way forward, especially in
view of Álvaro's recent work in that area. But it sort of sounds like
you're just trying to sink the patch despite it being a feature that
is both in the SQL standard and has real use cases which have been
mentioned on the thread, and I don't really like that. In the interest
of full disclosure, I do work at the same company as Dilip and
Himanshu, so I might be biased. But I feel like I would be in favor of
this feature no matter who proposed it, as long as it was
well-implemented. It's always struck me as odd that we allow deferring
some types of constraints but not others, and I don't understand why
we'd want to block closing that gap unless there is some concrete
downside to so doing.

--
Robert Haas
EDB: http://www.enterprisedb.com