While Loop entire select Tag - php

Question

Is it possible to while loop an entire select tag to have multiple dropdown menus?
What I am trying to achieve is to have a column full of dropdown menus in a table.
This is what I have tried so far
<?php
$DNS_FROM = $DNS."_port-%";
$select = "SELECT * FROM `uplink_port_mapping` WHERE DNS_From LIKE '$DNS_FROM'";
$select1 = mysqli_query($conn, $select);
$select2 = "SELECT DNS_From FROM `uplink_port_mapping` WHERE DNS_From NOT LIKE '$DNS_FROM' AND DNS_To = ''";
$select3 = mysqli_query($conn, $select2);
while($uplink_from = mysqli_fetch_assoc($select1)){
echo "<tr>";
echo "<td>".$uplink_from['DNS_From']."</td>";
echo "<td>"."<select name = 'uplink_to' multiple='multiple'>
<option value = '".$uplink_from['DNS_To']."' selected='selected'>". $uplink_from['DNS_To']."</option>";
while ($uplink_to = mysqli_fetch_assoc($select3)){
echo "<option value='".$uplink_to['DNS_From']."'>".$uplink_to['DNS_From']."</option>";
}
echo"</select>";
echo"</td>";
echo"</tr>";
}
?>
How it is right now.

Answer 1

The reason for the second while loop only working once is, that mysqli_fetch_assoc($result) will leave the pointer of the $result recource at it's end.
So when you try to loop the second time, mysqli_fetch_assoc($result) will not return anything (cause it's at the end of the $result recource.
Two possibilites:
Reset the pointer to the beginning:
<?php
....
while($uplink_from = mysqli_fetch_assoc($select1)){
echo "<tr>";
echo "<td>".$uplink_from['DNS_From']."</td>";
echo "<td>"."<select name = 'uplink_to' multiple='multiple'>
<option value = '".$uplink_from['DNS_To']."' selected='selected'>". $uplink_from['DNS_To']."</option>";
// here's the change:
mysql_data_seek($select3, 0);
while ($uplink_to = mysqli_fetch_assoc($select3)){
echo "<option value='".$uplink_to['DNS_From']."'>".$uplink_to['DNS_From']."</option>";
}
echo"</select>";
echo"</td>";
echo"</tr>";
}
....
?>
Or - which I think is the better solution - store that data into an array first, and then walk through that array:
<?php
...
$select2 = "SELECT DNS_From FROM `uplink_port_mapping` WHERE DNS_From NOT LIKE '$DNS_FROM' AND DNS_To = ''";
$result2 = mysqli_query($conn, $select2);
$dns_from = Array();
while ($uplink_to = mysqli_fetch_assoc($select3)){
$dns_from[] = $uplink_to;
}
....
// inside your first while loop:
foreach($dns_from as $dns) {
echo "<option value='".$dns['DNS_From']."'>".$dns['DNS_From']."</option>";
}
....
// note that I left out a bunch of your code, that doesn't change.
?>

Answer 2

Multiple select dropdown basic examples
$array = [
'Apple' => 1,
'Orange' => 0,
'Banana' => 1,
];
echo '<select multiple>';
foreach ($array as $fruit => $sel) {
$selected = 0;
if ($sel == 1) {
$selected = 'selected';
}
echo '<option value="' . $fruit . ' " ' . $selected . '>' . $fruit . '</option>';
}
echo '</select>';