http://greemranqq.iteye.com/blog/2072878
http://www.mysqlab.net/
http://www.mysqlpub.com/
http://blog.163.com/li_hx/blog/static/18399141320146219354154
http://isky000.com/database/mysql-explain-detail
http://blog.csdn.net/wangpeng047/article/details/12849331
http://www.cnblogs.com/cswuyg/p/4355948.html