Re: COMMENTS are not being copied in CREATE TABLE LIKE

From: "Matheus Alcantara" <matheusssilv97(at)gmail(dot)com>
To: "Jim Jones" <jim(dot)jones(at)uni-muenster(dot)de>, "pgsql-hackers(at)lists(dot)postgresql(dot)org" <pgsql-hackers(at)lists(dot)postgresql(dot)org>
Cc: "Matheus Alcantara" <matheusssilv97(at)gmail(dot)com>
Subject: Re: COMMENTS are not being copied in CREATE TABLE LIKE
Date: 2026-02-12 14:36:26
Message-ID: DGD24UA7LASG.11H30IV2AFVA2@gmail.com
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Hi, thanks for checking this.

On Thu Feb 12, 2026 at 7:11 AM -03, Jim Jones wrote:
> Hi,
>
> While reviewing another patch[1] I saw that COMMENTS on tables are being
> ignored in CREATE TABLE LIKE:
>
> psql (18.1 (Debian 18.1-1.pgdg13+2))
> Type "help" for help.
>
> postgres=# \pset null '(null)'
> Null display is "(null)".
> postgres=# CREATE TABLE t1 (id int, name text);
> COMMENT ON TABLE t1 IS 'table comment';
> CREATE TABLE t2 (LIKE t1 INCLUDING ALL);
> CREATE TABLE t3 (LIKE t1 INCLUDING COMMENTS);
>
> SELECT
> obj_description('t1'::regclass, 'pg_class') AS t1_comment,
> obj_description('t2'::regclass, 'pg_class') AS t2_comment,
> obj_description('t3'::regclass, 'pg_class') AS t3_comment;
> CREATE TABLE
> COMMENT
> CREATE TABLE
> CREATE TABLE
> t1_comment | t2_comment | t3_comment
> ---------------+------------+------------
> table comment | (null) | (null)
> (1 row)
>
>
> v1 attached attempts to fix it by expanding expandTableLikeClause() to
> retrieve and copy the table-level comment when the INCLUDING COMMENTS
> [ALL] option is specified:
>

The patch fix the issue and it seems correct to me.

This bug seems to also happen on 14.20:
postgres=# select version();
version
------------------------------------------------------------------------------------------------------------------------------
PostgreSQL 14.20 (Homebrew) on aarch64-apple-darwin24.6.0, compiled by Apple clang version 17.0.0 (clang-1700.4.4.1), 64-bit
(1 row)

postgres=# CREATE TABLE t(a int, b text);
CREATE TABLE
postgres=# COMMENT ON TABLE t IS 'foo';
COMMENT
postgres=# CREATE TABLE t2(LIKE t INCLUDING ALL);
CREATE TABLE
postgres=# SELECT obj_description('t'::regclass, 'pg_class') as t_comment, obj_description('t2'::regclass, 'pg_class') AS t2_comment;
t_comment | t2_comment
-----------+------------
foo |
(1 row)

So I think that we need to backport.

--
Matheus Alcantara
EDB: https://www.enterprisedb.com

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