Understanding var_dump() for result-set of SQL Query.

Here is my snippet for which am trying to understnad output of var_dump().

echo "<br> <br> Part2: ";
$query1="select * from student";
$result=mysqli_query($con,$query1) or die(mysqli_error($con));
var_dump($result);
if ($result)
{
    $num1=mysqli_num_rows($result);
    var_dump($num1);
    echo $num1." rows affected.";
}

OUTPUT:

<---- Any explanation for this output?

[pritaeas]

Am not sure what needs explaining. The result returned by a mysqli_query is a result object.

Why are all the identifiers set to null ?

[pritaeas]

It gets it's values after a fetch or seek.

Wasn't num_rows supposed to contain number of rows affected ?

[pritaeas]

Not necessarily. If it did, there would be no need for the mysqli_num_rows function.