First while loop stops when second while loop ends - php

Question

I'm beginner and I'm trying to make a simple navigation menu with a dropdown but the first loop stops when the nested loop is completed. Is there any suggestion? Please be analytic because of my low programming skills.
<?php
function nav_main($dbc, $path) {
$q = "SELECT * FROM navigation ORDER BY position ASC";
$r = mysqli_query($dbc, $q);
while($nav = mysqli_fetch_assoc($r)) {
$nav['slug'] = get_slug($dbc, $nav['url']);
if($nav['parent_id'] == 0) {
?>
<li<?php selected($path['call_parts'][0], $nav['slug'], ' class="active"') ?>><?php echo $nav['label']; ?></li>
<?php
}
elseif ($nav['parent_id'] == 1) {
?>
<li class="dropdown<?php selected($path['call_parts'][0], $nav['slug'], ' active"') ?>"><?php echo $nav['label']; ?><span class="caret"></span>
<ul class="dropdown-menu">
<?php
while($subnav = mysqli_fetch_assoc($r)) {
$subnav['slug'] = get_slug($dbc, $subnav['url']);
if($subnav['parent_id'] == 3) {
?>
<li><?php echo $subnav['label']; ?></li>
<li role="separator" class="divider"></li>
<?php
}
}
?>
</ul>
</li>
<?php
}
}
}
?>

Answer 1

Both your while loops are processing the same result set!
So obviously when the second while loop finishes the resultset is completely consumed and there is nothing left for the outer while look to do but terminate.
This is a precise of what you are doing :-
$q = "SELECT * FROM navigation ORDER BY position ASC";
$r = mysqli_query($dbc, $q);
// first while loop
while($nav = mysqli_fetch_assoc($r)) {
// inner while loop
while($subnav = mysqli_fetch_assoc($r)) {
Both are using $r and therefore regardless of you using a different variable to hold the returned row data the inner loop will consume row 2->end of the same result set as is being processed in the outer while loop