Postgres 15

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-- create extension "uuid-ossp" schema ext;  -- not possible here

CREATE TABLE profiles (id int GENERATED always AS IDENTITY PRIMARY KEY);
INSERT INTO profiles (id) VALUES (DEFAULT)
RETURNING *;

CREATE TABLE

id

1

INSERT 0 1

ALTER TABLE profiles ALTER COLUMN id DROP IDENTITY IF EXISTS;
ALTER TABLE profiles
  ALTER COLUMN id TYPE UUID USING md5(id::text)::UUID
, ALTER COLUMN id SET DEFAULT md5(now()::text)::uuid;  -- dummy in place of "uuid_generate_v4()"

ALTER TABLE

ALTER TABLE

INSERT INTO profiles (id) VALUES (DEFAULT);
TABLE profiles;

INSERT 0 1

id

c4ca4238-a0b9-2382-0dcc-509a6f75849b

6abb9219-4b3b-807f-fca8-8cdd8166450d

SELECT 2