Re: BUG #17435: "add column if not exists" always adds new FK on the column

On Sat, 12 Mar 2022 at 07:43, PG Bug reporting form <noreply@postgresql.org> wrote:
> The following bug has been logged on the website:
>
> Bug reference:      17435
> Logged by:          Rafael Sousa
> Email address:      rafmsou@gmail.com
> PostgreSQL version: 12.10
> Operating system:   macOS, linux
> Description:
>
> The statement below aims to add a new column CCC on table XXX and create a
> FK constraint to YYY at the same time:
>
> "alter table XXX add column if not exists CCC uuid references YYY (id);"
>
> I checked the docs and other forum and that seems to be possible. The
> problem is that we end up with multiple FKs created on column CCC when
> running the statement multiple times. I would hope no FK gets created when
> the column already exists, is that correct?

It seems this bug has been fixed in 1281a5c907 [1].  However, it doesn't backpatch to v12.

[1] https://git.postgresql.org/gitweb/?p=postgresql.git;a=commit;h=1281a5c907

--
Regrads,
Japin Li.
ChengDu WenWu Information Technology Co.,Ltd.