这里似乎已经有几个问题。您尝试过他们的解决方案吗?
相关部分在这里:
At the time of building this gem, the necessary DLL files where available
in the following download:
http://dev.MysqL.com/get/Downloads/Connector-C/mysql-connector-c-noinstall-6.0.2-win32.zip/from/pick
And put lib\libMysqL.dll file in your Ruby bin directory, for example
C:\Ruby\bin