Date: Thu, 17 Sep 2026 09:51:54 +0000
To: pgsql-bugs@lists.postgresql.org
From: Ludvig Janiuk <ludvig.janiuk@proton.me>
Subject: 42P16 error when dropping and adding column
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Hello, it seems that between pqsl 17 and 18, the behavior of the=20
following reproducer has changed:

=3D=3D=3D=3D
CREATE TABLE reproducer(id int NOT NULL); ALTER TABLE reproducer DROP=20
COLUMN "id", ADD COLUMN "id" int, ADD PRIMARY KEY("id");
=3D=3D=3D=3D

Expected output (this is the case on psql 16 and 17):

=3D=3D=3D=3D
CREATE TABLE
ALTER TABLE
=3D=3D=3D=3D

Actual output (on=C2=A0psql (PostgreSQL) 18.6 (Ubuntu 18.6-0ubuntu0.26.04.1=
)):

=3D=3D=3D=3D
CREATE TABLE
ERROR:=C2=A0 42P16: primary key column "id" is not marked NOT NULL
LOCATION:=C2=A0 index_check_primary_key, index.c:266
=3D=3D=3D=3D

I could not find anything direcly related in the change notes=20
(https://www.postgresql.org/docs/release/18.0/). There were a few lines=20
related to NULL, but with my knowledge I could not be sure if they were=20
relevant.

I hope you can accept my bug report, or let me know the reason why if=20
this is correct behavior.

Best regards,

--=20
//Ludvig Janiuk