Who knows is there any tools, modules or whatever to convert existing table dump and structure into UpgradeData, UpgradeSchema? Why? For example you created complicated settings stored in DB and you want to apply it to another installation along with your module to initialize it during installation. There is no way to build UpgradeData manually without any error or typo if it is big enough.
Yes, I know, I can insert it from sql file, but it is not always suitable