Thread: COPY documentation with regard to references constraints

I was unable to find any documentation clarifying if using COPY to load a 
table with rows referencing others rows in the same table, whether I 
had to worry about ordering of the input.
What I found (in 17) is that even if the references constraint wasn't 
set as deferrable, I could have rows for children before their parents 
in the COPY data and things still worked.

On Thu, Oct 31, 2024 at 1:04 PM Bruno Wolff III <bruno@wolff.to> wrote:
> I was unable to find any documentation clarifying if using COPY to load a
> table with rows referencing others rows in the same table, whether I
> had to worry about ordering of the input.
> What I found (in 17) is that even if the references constraint wasn't
> set as deferrable, I could have rows for children before their parents
> in the COPY data and things still worked.

AFAIK, DEFERRABLE is for temporary violations crossing statement boundaries,
to postpone the enforcement of FKs at COMMIT time of the transaction.

While a single COPY is just one statement, so whether a temporary violation
for self-referential FKs would occur would be implementation-dependent,
and thus "neither logical" nor predictable.

Applies to other statement types too.

But of course, more authoritative answers will come I'm sure. --DD

On Thu, Oct 31, 2024 at 13:15:34 +0100,
  Dominique Devienne <ddevienne@gmail.com> wrote:
>
>AFAIK, DEFERRABLE is for temporary violations crossing statement boundaries,
>to postpone the enforcement of FKs at COMMIT time of the transaction.
>
>While a single COPY is just one statement, so whether a temporary violation
>for self-referential FKs would occur would be implementation-dependent,
>and thus "neither logical" nor predictable.
>
>Applies to other statement types too.

Thanks. I needed to look more carefully under deferrable where it says 
the following:
This controls whether the constraint can be deferred. A constraint that is 
not deferrable will be checked immediately after every command.

That is pretty clear.

On Thu, 2024-10-31 at 06:38 -0500, Bruno Wolff III wrote:
> I was unable to find any documentation clarifying if using COPY to load a
> table with rows referencing others rows in the same table, whether I
> had to worry about ordering of the input.

I cannot find it in the documentation either, but since COPY is a single
statement and foreign key constraints are checked at the end of the
statement, it should work fine.

Yours,
Laurenz Albe