Solving PHP Warning mysqli_num_rows() expects, boolean given

[arnage]

Well, here it is, usually problematic part of code is like:

$query = mysqli_query($conn, 'SELECT COUNT(`id`) FROM `table` WHERE `id` = '.$id.'');
    $count = mysqli_num_rows($query); 

... which is throwing error:

PHP Warning:  mysqli_num_rows() expects parameter 1 to be mysqli_result, boolean given in /www/user/public_html/index.php on line 2

... so the query must be in if():

if ($query = mysqli_query($conn, 'SELECT COUNT(`id`) FROM `table` WHERE `id` = '.$id.'')) {
    $count = mysqli_num_rows($query);
} 

But this is throwing this error:

PHP Notice:  Undefined variable: count in /www/user/public_html/index.php on line 2

... so simple define it:

// if you want integer:
$count = (int)''; // perfectly valid way
// if you want string:
$count = '';
// or use settype(): http://php.net/manual/en/function.settype.php
settype($count, 'int');
if ($query = mysqli_query($conn, 'SELECT COUNT(`id`) FROM `table` WHERE `id` = '.$id.'')) {
    $count = mysqli_num_rows($query);
} 

And there will be no Warning nor Notice.