我关注了这篇文章，http://blog.teamtreehouse.com/installing-ruby-rails-and-mysql-on-os-x-lion。
我一直在学习Ruby和Rails一个月，所以我对Ruby很熟悉。由于通过以下几个教程获得的理解，我也了解Rails的一些部分。
但是，在gem install mysql之前，我一直未能gem install mysql2或rails new photos -d mysql。
我已成功完成brew install mysql并已检查mysql -u root。
seodongju@Seoui-MacBook-Pro ~/Desktop/Projects$ sudo gem install mysql2
Password:
Building native extensions. This could take a while...
ERROR: Error installing mysql2: ERROR: Failed to build gem native extension.
/usr/local/rvm/rubies/ruby-2.0.0-p247/bin/ruby extconf.rb
checking for rb_thread_blocking_region()... yes checking for rb_wait_for_single_fd()... yes checking for rb_hash_dup()... yes checking for rb_intern3()... yes checking for mysql.h... no
checking for mysql/mysql.h... no
mysql.h is missing. please check your installation of mysql and try again.
*** extconf.rb failed *** Could not create Makefile due to some reason, probably lack of necessary libraries and/or headers. Check the mkmf.log file for more details. You may need configuration options.
Provided configuration options: --with-opt-dir --with-opt-include --without-opt-include=${opt-dir}/include --with-opt-lib --without-opt-lib=${opt-dir}/lib --with-make-prog --without-make-prog --srcdir=. --curdir --ruby=/usr/local/rvm/rubies/ruby-2.0.0-p247/bin/ruby --with-mysql-config --without-mysql-config
Gem files will remain installed in /usr/local/rvm/gems/ruby-2.0.0-p247/gems/mysql2-0.3.13 for inspection. Results logged to /usr/local/rvm/gems/ruby-2.0.0-p247/gems/mysql2-0.3.13/ext/mysql2/gem_make.out