下载文件的点击数回填_PHP

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
{
?>

click here download


};?>

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");
?>