PHP-登录页面

if($_POST){
    $use=trim($_POST['user']);
    $pass=md5($_POST['pasd']);
    $conn=new mysqli('127.0.0.1','root','root','ccc');
    $sql="select * from admin where user='$use' and pasd='$pass'";
    $res=$conn->query($sql);
    if($res->num_rows>0){
        setcookie('admin',1);
        header('location:index.php');
    }else{
        echo '<script>alert("用户名或者密码错误")</script>';
    };

}