Errors Installing mysql2 gem via the Bundler

Answer was similar to the one Wrikken posted -- here's what I did to fix it for the sake of future readers.

(This is for RHEL 5.5 -- similar but different commands apply for Ubuntu/Debian/etc.)

Doing sudo yum list installed will print out all installed packages on your machine (note: yum on RHEL requires you add a Red Hat Network repository [I use EPEL], and run it via sudo).

I had mysql and mysql-server, which explained why MySQL worked fine for every pre-existing app, but no mysql-devel, which is necessary to fix that mysql.h is missing error and similar other build errors.

Long story short, after a mysqldump -u root -ppassword --all-databases > full-dump.sql for safety, it was fixed with a simple

sudo yum install mysql-devel

For Ubuntu have to install following.libmysqlclient-devlibmysqlclient16

For Mac with a brew install of mysql the following solution fixed the problem for me:

I edited the mysql_config file in /usr/local/Cellar/mysql/5.6.12/bin and removed the W-compiler options -Wno-null-conversion and -Wno-unused-private-field for cflags and cxxflags.

This solved the problem with "gem install mysql2".

Reference: http://www.randomactsofsentience.com/2013/05/gem-install-mysql2-missing-mysqlh-on-os.html