I'm glad it was helpful. Thank you for your hard work studying. I also appreciate it. You're trying to implement a web app, and you're doing it alone. It's not easy, but I think it's a big challenge. If I talk about DB, I think design, implementation, and the test data environment that is the target during development are important. When developing, creating 'plausible' development data is also a very important part, and the more diverse the development data that can be tested, the less additional modifications and supplements will occur in the business logic part such as HTML, Java, and Node.js later. Likewise, when developing by team, the integration test or deadline schedule is significantly affected depending on how many sufficient and diverse cases (expected user input format, data consistency check upon input, appropriateness of time or date, etc.) are included in the development data. Please visit my YouTube channel or Infraon, where related courses are registered, so it would be good to refer to them. I'll leave the URL below. https://www.youtube.com/playlist?list=PL_RECGqDS3icOhnWgOTFF5-CBto3OXj4l Thank you for asking many questions and cross-checking, which is not easy for a student.