Fatal error:  Call to undefined function mysql_num_row() in E:\phpStudy\WWW30\daima\login_a.php on line 33

if(mysql_num_row($result)==0){

說是這一句，下面是完整程式碼

<?php 

#session_start() ;

$username=$_POST["username"];

$password=$_POST["password"];

include("config.php");

if(empty($username)){

echo ("<script type='text/javascript'> alert('使用者名稱不能是空的');history. go(-1);</script>");

}

if(empty($password)){

echo ("<script type= 'text/javascript'> alert('密碼不能是空的');history.go(-1);</script>");

}

//echo $username.$password;

#$db=mysql_connect("127.0.0.1","root","root");

mysql_select_db("performance",$db);

 mysql_query("SET NAMES 'GB2312'");

 $_POST["username"];

$sql="select * from admin where admin_name='$username' and admin_pw='$password'";

$result=mysql_query($sql);

//$number = mysql_fetch_row($result);

//$result=mysql_fetch_array(mysql_query($sql));

if(mysql_num_row($result)== 0){

echo ("<script type='text/javascript'> alert('使用者名稱或密碼不正確！ ');history.go(-1);</script>");

mysql_close();

exit;

}else{

$_SESSION["admin"]="lee";

echo "<script>location.href='Admin.html';</script>";

}

?>