Normally we would do something like rails new APP_PATH but we have the option to preconfigure for selected database namely: mysql, oracle, postgresql, sqlite3, frontbase, ibm_db, sqlserver, jdbcmysql, jdbcsqlite3, jdbcpostgresql, jdbc

Usage:
    rails new APP_PATH [options]

Options:
    -d, [--database=DATABASE]

So we could use $rails new projectname -d mysql the specify the port in the database config file, config/database.yml.

development:
  adapter: mysql2
  encoding: utf8
  database: <YOURDBNAME_development>
  pool: 5
  username: <YOUR_USERNAME>
  password: <YOUR_PASSWORD>
  host: localhost
  port: 3306

test:
  adapter: mysql2
  encoding: utf8
  database: <YOURDBNAME_test>
  pool: 5
  username: <YOUR_USERNAME>
  password: <YOUR_PASSWORD>
  host: localhost
  port: 3306

production:
  adapter: mysql2
  encoding: utf8
  database: <YOURDBNAME_production>
  pool: 5
  username: <YOUR_USERNAME>
  password: <YOUR_PASSWORD>
  host: localhost
  port: 3306

If you are using MAMP, you can use the sockets instead;

development:
  adapter: mysql2
  encoding: utf8
  database: <YOURDBNAME_development>
  pool: 5
  username: <YOUR_USERNAME>
  password: <YOUR_PASSWORD>
  host: localhost
  socket: '/Applications/MAMP/tmp/mysql/mysql.sock'

test:
  adapter: mysql2
  encoding: utf8
  database: <YOURDBNAME_test>
  pool: 5
  username: <YOUR_USERNAME>
  password: <YOUR_PASSWORD>
  host: localhost
  socket: '/Applications/MAMP/tmp/mysql/mysql.sock'

production:
  adapter: mysql2
  encoding: utf8
  database: <YOURDBNAME_production>
  pool: 5
  username: <YOUR_USERNAME>
  password: <YOUR_PASSWORD>
  host: localhost
  socket: '/Applications/MAMP/tmp/mysql/mysql.sock'

Check out this other post that has details on installation of Rails on OS X (MySQL included).

Ps: Find out more options from rails --help

Ps 2: For those using Rails & MAMP (using sockets, which seems to be the easier option) … I’m not quite sure if it works out of the box. I was tinkering with an actual MySQL install using homebrew by the time I found this solution. If it doesn’t, try install MySQL using homebrew first. There have been a few articles on the web discussing the fact that the MySQL bundled with MAMP doesn’t have everything reuired for a full MySQL installation (which might be necessary for the mysql2 gem install).

1. Stack Overflow: Convert a Ruby on Rails app from sqlite to MySQL? … shows you step by step guide on how to migrate an existing SQLite DB to MySQL.
2. Stack Overflow: Using SQLite vs. MySQL with Ruby? … debate on which is the better way to go. Personally I prefer MySQL.