If you installed the latest mysql with homebrew, my version of mysql was 5.6.12. I couldn't install mysql2 gem
gem install mysql2
will output
/Users/anton/.rbenv/versions/1.9.3-p286/bin/ruby extconf.rb
checking for rb_thread_blocking_region()... yes
checking for rb_wait_for_single_fd()... 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.
....
after checking forums, relinking include paths and failing at everything else, turns out it doesn't work for mysql version 5.6.12, so that answer on stackoverflow helped me.
http://stackoverflow.com/a/17252887/987533
Copy of solution:
Uninstall MySQL 5.6.12:
brew unlink mysql
brew uninstall mysql
Go to the homebrew directory:
cd /usr/local
Go to version 5.6.10 (you can find a list of versions by running brew versions mysql:
git checkout 48f7e86 Library/Formula/mysql.rb
Then install mysql again:
brew install mysql
And install gem
gem install mysql2