Re: BUG #16805: "ALTER TABLE ... ADD COLUMN IF NOT EXISTS ... PRIMARY KEY" fails if column exists and is the primary

I'm unable to reproduce this issue on CentOS7. Here's what I get:

------------------------------------------------------------
psql (12.5)
Type "help" for help.

postgres=# create table foo ( bar text );
CREATE TABLE
postgres=# alter table if exists foo add column if not exists id bigserial;
ALTER TABLE
postgres=# alter table if exists foo add column if not exists id bigserial;
NOTICE: column "id" of relation "foo" already exists, skipping
ALTER TABLE
------------------------------------------------------------

Can you please confirm if you are building from source or using any
standard postgresql packages?

On Tue, Jan 5, 2021 at 2:55 PM PG Bug reporting form <noreply(at)postgresql(dot)org>
wrote:

> The following bug has been logged on the website:
>
> Bug reference: 16805
> Logged by: Doug Perham
> Email address: dperham(at)opex(dot)com
> PostgreSQL version: 12.5
> Operating system: Ubuntu 20.04
> Description:
>
> ALTER TABLE IF EXIST foo ADD COLUMN IF NOT EXISTS id BIGSERIAL PRIMARY
> KEY;
> Fails if "id" exists and is already the primary key.
>
> It seems that everything should be okay if "id" exists and is the primary
> key. Instead, an error is thrown as follows:
>
>
> test=# create table foo ( bar text );
> CREATE TABLE
> test=# alter table if exists foo add column if not exists id bigserial
> primary key;
> ALTER TABLE
> test=# alter table if exists foo add column if not exists id bigserial
> primary key;
> NOTICE: column "id" of relation "foo" already exists, skipping
> ERROR: multiple primary keys for table "foo" are not allowed
>
>

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