【Rails8】heroku postgresのdatabase.ymlの書き方

herokuのドキュメントには以下のように書いてますが...

# PostgreSQL. Versions 9.3 and up are supported.
#
(中略)
production:
  primary: &primary_production
    <<: *default
    database: myapp_production
    username: myapp
    password: <%= ENV["MYAPP_DATABASE_PASSWORD"] %>
  cache:
    <<: *primary_production
    database: myapp_production_cache
    migrations_paths: db/cache_migrate
  queue:
    <<: *primary_production
    database: myapp_production_queue
    migrations_paths: db/queue_migrate
  cable:
    <<: *primary_production
    database: myapp_production_cable
    migrations_paths: db/cable_migrate

これだと自分はうまくいかず、以下にするとうまくいきました
（user_name, passwordではなくurl: <%= ENV['DATABASE_URL'] %>に）

# PostgreSQL. Versions 9.3 and up are supported.
#
(中略)
production:
  primary: &primary_production
    <<: *default
    database: myapp_production
    url: <%= ENV['DATABASE_URL'] %>
  cache:
    <<: *primary_production
    database: myapp_production_cache
    migrations_paths: db/cache_migrate
  queue:
    <<: *primary_production
    database: myapp_production_queue
    migrations_paths: db/queue_migrate
  cable:
    <<: *primary_production
    database: myapp_production_cable
    migrations_paths: db/cable_migrate