php代码中的错误：尝试验证记录是否存在[重复]

I was trying to check whether a particular rno was existing in any specific table role. Both rno and role was fetched from html form. Could some one help?

   <?php

 $rno=$_POST['rno'];
 $role=$_POST['role'];

$con = new  mysqli("localhost", "root", "", "premierlg");

if ($con->connect_error) {
    die("Connection failed: " . $conn->connect_error);
} 

$query = mysqli_query($con, "SELECT * FROM" .$rno. " WHERE rno='".$rno."'");

if(mysqli_num_rows($query) > 0){

    echo "Record already exists";
}else{
    echo "Dosen't exist.";
if (!mysqli_query($con,$query))
    {
        die('Error: ' . mysqli_error($con));
    }
}

?>

</div>