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References: <19445-f919d77c0e4f8d10@postgresql.org>
In-Reply-To: <19445-f919d77c0e4f8d10@postgresql.org>
From: Junwang Zhao <zhjwpku@gmail.com>
Date: Mon, 30 Mar 2026 22:56:55 +0800
Message-ID: <CAEG8a3LwRiXzGp94y3o7DPK59UCXG95Gx3yWFtGQCpVUEL9RvQ@mail.gmail.com>
Subject: Re: BUG #19445: Domain DEFAULT not recorded in pg_attrdef (atthasdef
 false) in PostgreSQL 18.3
To: zheng_xianghang@163.com, pgsql-bugs@lists.postgresql.org
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On Mon, Mar 30, 2026 at 7:52=E2=80=AFPM PG Bug reporting form
<noreply@postgresql.org> wrote:
>
> The following bug has been logged on the website:
>
> Bug reference:      19445
> Logged by:          Xianghang Zheng
> Email address:      zheng_xianghang@163.com
> PostgreSQL version: 18.3
> Operating system:   Linux x86_64
> Description:
>
> 1. PostgreSQL Version
> PostgreSQL 18.3 (x86_64)
> 2. Operating System
> Linux x86_64
> 3. Problem Description
> When a table column uses a domain that has a DEFAULT value, the column's
> pg_attribute.atthasdef is false, and no entry exists in pg_attrdef.
> However, the domain default value works correctly at runtime.
> This is a system catalog metadata bug.
> 4. Steps to Reproduce
> CREATE DOMAIN my_arr_domain AS int[] DEFAULT '{}';
> CREATE TABLE t (col my_arr_domain);
> SELECT
>     a.attname,
>     a.atthasdef,
>     pg_get_expr(adbin, adrelid) as default_value
> FROM pg_attribute a
> LEFT JOIN pg_attrdef d ON a.attrelid =3D d.adrelid AND a.attnum =3D d.adn=
um
> WHERE a.attrelid =3D 't'::regclass AND a.attnum > 0;
> INSERT INTO t DEFAULT VALUES;
> SELECT * FROM t;
> 5. Actual Result
> atthasdef =3D f
> default_value is empty
> But insert returns the correct default {}
> 6. Expected Result
> atthasdef should be true
> System catalog must correctly reflect the default inherited from the doma=
in
> 7. Additional Information
> - Domain default works correctly
> - System metadata is wrong
> - Affects pg_dump, information_schema, and 3rd party tools
> - Bug exists in latest stable PostgreSQL 18.3

I think this is by design, postgres correctly distinguishes between column-=
level
defaults (stored in pg_attrdef) and type/domain-level defaults.

>
> -------------------------------------------------------------------------=
----------------------------
>
>
> postgres=3D# select version();
>                                                  version
> -------------------------------------------------------------------------=
--------------------------------
>  PostgreSQL 18.3 on x86_64-pc-linux-gnu, compiled by gcc (GCC) 4.8.5
> 20150623 (Red Hat 4.8.5-44), 64-bit
> (1 row)
>
> postgres=3D#
> postgres=3D# DROP TABLE IF EXISTS t CASCADE;
> INSERT INTO t DEFAULT VALUES;
> SELECT * FROM t;
>
> DROP TABLE t;
> DROP DOMAIN my_arr_domain CASCADE;DROP TABLE
> postgres=3D# DROP DOMAIN IF EXISTS my_arr_domain CASCADE;
> DROP DOMAIN
> postgres=3D#
> postgres=3D# CREATE DOMAIN my_arr_domain AS int[] DEFAULT '{}';
> CREATE DOMAIN
> postgres=3D#
> postgres=3D# CREATE TABLE t (col my_arr_domain);
> CREATE TABLE
> postgres=3D#
> postgres=3D# SELECT
> postgres-#     a.attname,
> postgres-#     a.atthasdef,
> postgres-#     pg_get_expr(adbin, adrelid) as default_value
> postgres-# FROM pg_attribute a
> postgres-# LEFT JOIN pg_attrdef d ON a.attrelid =3D d.adrelid AND a.attnu=
m =3D
> d.adnum
> postgres-# WHERE a.attrelid =3D 't'::regclass
> postgres-#   AND a.attnum > 0;
>  attname | atthasdef | default_value
> ---------+-----------+---------------
>  col     | f         |
> (1 row)
>
> postgres=3D#
> postgres=3D# INSERT INTO t DEFAULT VALUES;
> INSERT 0 1
> postgres=3D# SELECT * FROM t;
>  col
> -----
>  {}
> (1 row)
> postgres=3D# DROP TABLE t;
> DROP TABLE
> postgres=3D# DROP DOMAIN my_arr_domain CASCADE;
> DROP DOMAIN
> postgres=3D#
>
>
>
>


--=20
Regards
Junwang Zhao