CREATE TABLE IF NOT EXISTS messages (
  id          uuid        PRIMARY KEY DEFAULT gen_random_uuid(),
  channel_id  uuid        NOT NULL REFERENCES channels (id) ON DELETE CASCADE,
  user_id     uuid        REFERENCES users (id) ON DELETE SET NULL,
  parent_id   uuid        REFERENCES messages (id) ON DELETE SET NULL,
  body_md     text        NOT NULL,
  created_at  timestamptz DEFAULT now(),
  edited_at   timestamptz
);