mysql日期类型比较

mysql日期类型对比：

日期类型详情参照http://www.jb51.net/article/23966.htm#comments
http://www.cnblogs.com/1130136248wlxk/articles/5238538.html
http://www.cnblogs.com/wenzichiqingwa/archive/2013/03/05/2944485.html