Postgres 15

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SELECT typname, typnamespace::regnamespace, typdefaultbin, typdefault
FROM   pg_type
WHERE  typdefaultbin IS NOT NULL
OR     typdefault IS NOT NULL;

typname
typnamespace
typdefaultbin
typdefault

time_stamp
information_schema
{SQLVALUEFUNCTION :op 4 :type 1184 :typmod 2 :location 105}
CURRENT_TIMESTAMP(2)

SELECT 1

CREATE DOMAIN text_x AS TEXT
DEFAULT 'X';

CREATE TABLE tbl1 (
   col_no_default text_x
 , col_default    text_x DEFAULT NULL)
  ;
 
 CREATE TABLE tbl2 (
   col_no_default information_schema.time_stamp
 , col_default    information_schema.time_stamp DEFAULT NULL)
   ;

CREATE DOMAIN

CREATE TABLE

CREATE TABLE

INSERT INTO tbl1 DEFAULT VALUES RETURNING *;

col_no_default
col_default

X
null

INSERT 0 1

INSERT INTO tbl2 DEFAULT VALUES RETURNING *;

col_no_default
col_default

2023-05-11 17:33:08.49+01
null

INSERT 0 1