从manual上知道了MysqL_affected_rows函数当UPDATE前后的数据一样时会返回异常值， 下面有个方便的解决办法，从官方munual上看到 bdobrica at gmail dot com 留言的：
As a solution to the problem pointed in the post reffering to MysqL_affected_rows() returning 0 when you are making an update query and the fields are not modified although the query is valid,i'm posting the following function. It is very simple and based on a prevIoUs post.
<div class="codetitle"><a style="CURSOR: pointer" data="52468" class="copybut" id="copybut52468" onclick="doCopy('code52468')"> 代码如下: