之前可能需要从libmysql.dll生成libmysqlclient.a:
来源
cd C:\xampp-1.8.3\mysql\lib
C:\DevKit-tdm-32-4.5.2-20111229-1559-sfx\devkitvars.bat
pexports.exe libmysql.dll > libmysql.def
//来源：C:\strawberry\c\bin\pexports.EXE 幸亏安装了perl,否则不知道到哪里找这个pexports工具下了
dlltool --input-def libmysql.def --dllname libmysql.dll --output-lib libmysqlclient.a -k
c:\redmine-2.6.0>gem install mysql2 --version=0.3.16 --platform=ruby -- --with-mysql-include=C:\xampp-1.8.3\mysql\include --with-mysql-lib=C:\xampp-1.8.3\mysql\lib
Building native extensions. This could take a while...
Successfully installed mysql2-0.3.16
1 gem installed
Installing ri documentation for mysql2-0.3.16...
Installing RDoc documentation for mysql2-0.3.16...
cd c:\redmine-2.6.0
bundle install