Re: not null constraints, again

On 2024-Sep-20, Alvaro Herrera wrote:

> Yeah, there's a bunch of conflicts in current master. I rebased
> yesterday but I'm still composing the email for v4. Coming soon.

Okay, so here is v4 with these problems fixed, including correct
propagation of constraint names to children tables, which I had
inadvertently broken earlier. This one does pass the pg_upgrade tests
and as far as I can see pg_dump does all the correct things also. I
cleaned up the tests to remove everything that's unneeded, redundant, or
testing behavior that no longer exists.

I changed the behavior of ALTER TABLE ONLY <parent> ADD PRIMARY KEY, so
that it throws error in case a child does not have a NOT NULL constraint
on one of the columns, rather than silently creating such a constraint.
(This is how `master` currently behaves). I think this is better
behavior, because it lets the user decide whether they want to scan the
table to create that constraint or not. It's a bit crude at present,
because (1) a child could have a NO INHERIT constraint and have further
children, which would foil the check (I think changing
find_inheritance_children to find_all_inheritors would be sufficient to
fix this, but that's only needed in legacy inheritance not
partitioning); (2) the error message doesn't have an errcode, and the
wording might need work.

--
Álvaro Herrera PostgreSQL Developer — https://www.EnterpriseDB.com/
"Learn about compilers. Then everything looks like either a compiler or
a database, and now you have two problems but one of them is fun."
https://twitter.com/thingskatedid/status/1456027786158776329