Re: BUG #19445: Domain DEFAULT not recorded in pg_attrdef (atthasdef false) in PostgreSQL 18.3

On Mon, Mar 30, 2026 at 7:52 PM PG Bug reporting form
<noreply(at)postgresql(dot)org> wrote:
>
> The following bug has been logged on the website:
>
> Bug reference: 19445
> Logged by: Xianghang Zheng
> Email address: zheng_xianghang(at)163(dot)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 = d.adrelid AND a.attnum = d.adnum
> WHERE a.attrelid = 't'::regclass AND a.attnum > 0;
> INSERT INTO t DEFAULT VALUES;
> SELECT * FROM t;
> 5. Actual Result
> atthasdef = 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 domain
> 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=# 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=#
> postgres=# 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=# DROP DOMAIN IF EXISTS my_arr_domain CASCADE;
> DROP DOMAIN
> postgres=#
> postgres=# CREATE DOMAIN my_arr_domain AS int[] DEFAULT '{}';
> CREATE DOMAIN
> postgres=#
> postgres=# CREATE TABLE t (col my_arr_domain);
> CREATE TABLE
> postgres=#
> postgres=# 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 = d.adrelid AND a.attnum =
> d.adnum
> postgres-# WHERE a.attrelid = 't'::regclass
> postgres-# AND a.attnum > 0;
> attname | atthasdef | default_value
> ---------+-----------+---------------
> col | f |
> (1 row)
>
> postgres=#
> postgres=# INSERT INTO t DEFAULT VALUES;
> INSERT 0 1
> postgres=# SELECT * FROM t;
> col
> -----
> {}
> (1 row)
> postgres=# DROP TABLE t;
> DROP TABLE
> postgres=# DROP DOMAIN my_arr_domain CASCADE;
> DROP DOMAIN
> postgres=#
>
>
>
>

--
Regards
Junwang Zhao