js实现表单联动

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=gb2312">
<LINK href="style.css" type=text/css rel=stylesheet>
<title>无标题文档</title>
</head>
<script language="JavaScript">
function Options(str)
{
//alert(str);
//s=Number(str)+1;
var n=str.indexOf(":")+1;//:前面是文号，后面是文件类别
var num=str.substring(0,--n);
var num1=Number(num);
var sortname=str.substring(++n,10000);
window.document.form_opt.num.value = num;
window.document.form_opt.sortname.value = sortname;
    }
</script> 
<style type="text/css">
<!--
.style1 {color: #666666}
-->
</style>
 </head><body>
<form action="wenhao.php" method="post" name="form_opt">
  <select name="select1">
    <option value="1" selected>B教</option>
    <option value="2">A教</option>
  </select>
  <select name="book"  onChange="Options(window.document.form_opt.book.options[selectedIndex].value);">
<option selected>请选择教室
<?php 
  //Options(window.document.form_opt.book.options[selectedIndex].value);
$db=mysql_connect("localhost","root","333333") or die("数据库连接失败!");
   mysql_select_db("wenjianku",$db);
  $query="select  * from tablename";
$result=mysql_query($query,$db);
while($data=mysql_fetch_object($result))
    {
     
  $tmpname=$data->sortname;
      $sortnum=$data->sortnum;
    
         echo '<option value='.$sortnum.':'.$tmpname.'>'.$tmpname.'</option>';
     }
mysql_close($db);
?>
</select>
<input name="sortname"> 
<input type="text" name="num"> 号
<input type="submit" name="Submit" value="提交">
<input type="reset" name="Submit2" value="重置">
</form>