## -------------
## macOS
## -------------
brew install mysql@5.7 # mysql@5.6 / default mysql8

## ~/.bash_profile or ~/.zshrc
export PATH="/usr/local/opt/mysql@5.7/bin:$PATH"
export LDFLAGS="-L/usr/local/opt/mysql@5.7/lib"
export CPPFLAGS="-I/usr/local/opt/mysql@5.7/include"
export PKG_CONFIG_PATH="/usr/local/opt/mysql@5.7/lib/pkgconfig"

## source ~/.bash_profile or ~/.zshrc
# cd application_dir
gem install mysql2 # or bundle install

## -------------
## Linux (redhat)
## -------------
yum install mysql mysql-devel
gem install mysql2 # or bundle install