下载文件的点击数回填

需要名称为book的mysql数据库表
表中含有下列字段：
id   下载的文件的唯一标识
downnum  点击数

first.php
<?while($myrow = @mysql_fetch_array($result))
{
?>
<tr>
<td>
<?if(empty($myrow["downnum"])) echo "0"; else echo $myrow["downnum"]; ?>  
</td>
<td>
<a  href="ddload.php?purl=downfileurl&dnnum=<?echo $myrow['downnum'] ?>&id=<?echo $myrow['id']?>">click here download </a>
</td>
</tr>
<?};?>

ddload.php
<?
     include("data.inc.php");
     if($incerror)
     {
           echo $incerror;
           exit;
     }
     if(empty($dnnum)) $dnnum = 1;
     else $dnnum ++;
     $sql = "update book set downnum ='$dnnum' where id =$id";
     mysql_query($sql);
     mysql_close($connect);
     header("location:$purl");
?>