Note that it is in general not necessary for the referencing column to
be NULLABLE. If you defer the constraint checking, you can insert a
cyclic structure. Of course, it's no longer a tree then.
The tutorial-ness of the documentation was already pointed out and I
don't think it needs to be said there. We just would want to not imply
this (nullable) would be necessary.
Documentation-wise I liked to MariaDB approach very much, where the two
tables were named "parent table" and "child table" and at some point
you note that it is allowed for a table to be both. But this would be a
lot more invasive.
All the Best
Mario Wenzel
Am Mittwoch, dem 05.05.2021 um 21:17 -0700 schrieb David G. Johnston:
> On Thu, Apr 29, 2021 at 10:33 AM Tom Lane <tgl@sss.pgh.pa.us> wrote:
> > I'm inclined to propose adding an example a little further down, as
> > per the attached draft patch. This wouldn't help people who stop
> > reading after the section's first sentence, but we can't cover
> > everything in the first sentence.
> >
> >
>
>
> Given the tutorial nature of this section I agree with the approach.
>
> I did a read through of the patch and I like it; though I suggest
> changing "but non-NULL" to "while non-NULL".
>
> Thanks!
>
> David J.
>