After making a model, migrating, and checking the DB with Sequel Pro
I don't have the database I intended to create! Since it became, I will post the remedy as a memorandum.
After dealing with it by referring to the article of here, the solution was reached.
This is a rudimentary mistake, but comment out the selected part of the image below (SQLite3 in the gemfile).
bundle install --without production
Because I need to make a DB
bundle exec rake db:create
And was this necessary? Maybe it wasn't necessary because I was already doing it
You can now check the database on Sequel Pro.