This link: http://en.wikibooks.org/wiki/Ruby_on_Rails/ActiveRecord/Migrations describes rake db:create:all as follows:
rake db:create[:all]: If :all not specified then create the database defined in config/database.yml for the current RAILS_ENV. If :all is specified then create all of the databases defined in config/database.yml.
I really still didn't get the difference between having :all or not? Can you just clarify a bit? Especially that database.yml will already have databases?
Thanks.