Hello Suguru Iwata,
You are seeing empty data because, now you are connected to a new database which is very fresh.
You can see the data that you created in one database in another.
However mendix allow you to do data migration among databases.
you can refer the configuration here in the documentation: https://docs.mendix.com/howto/data-models/migrating-your-mendix-database/
Hope my answer helps.