http://www.cnblogs.com/zhangchaoyang/archive/2012/08/28/2660929.html
http://www.cnblogs.com/leoo2sk/archive/2011/07/10/mysql-index.html
http://www.cnblogs.com/zhangchaoyang/archive/2012/08/28/2660929.html
http://www.cnblogs.com/leoo2sk/archive/2011/07/10/mysql-index.html