This section describes the error that occurred when bundle install gem in Rails application and how to solve it.
Ruby on Rails 6.0.0
An error occurred while installing pg (1.2.3), and Bundler cannot continue. Make sure that `gem install pg -v '1.2.3' --source 'https://rubygems.org/'` succeeds before bundling.
Could not find gem 'pg (>= 0.18, < 2.0)' in any of the gem sources listed in your Gemfile.
It is an error such as.
How to solve
It was solved by the following command.
brew install postgres
It seems that I was stuck in postgresQL.