Getting multiple results without query inside loop - php

Question

I'm trying to improve the loading times of images and need to change around the code.
I haven't had any luck finding out how to do this and I'm not sure if it is even possible. In the example below you can see that I use KEY to match it with U_KEY to get FILE_PATH which I then add to a long comma delimited $allPaths string.
I know I should not use queries inside loops but I have no idea how to change this.
<?php
$sql = "SELECT * FROM test_users, image_uploads LIMIT 0, 27";
$result = mysqli_query($mysqli, $sql);
while($value = mysqli_fetch_array($result)) {
$files_key = $value["KEY"];
$allPaths = "";
$inner_query = "SELECT * FROM additional_uploads WHERE U_KEY = '".$files_key;
$inner_result = mysqli_query($mysqli, $inner_query);
while ($row = mysqli_fetch_array($inner_result)) {
$allpaths .= $row['FILE_PATH'].",";
}
// how do I get $allPaths without using a query inside the while loop?
}
?>
If someone could tell me how I can get $allPaths with only one query instead of multiple queries inside the loop as shown above it would probably load the images much faster.
Is this possible?
Edit
I have tried to understand the problem using the suggested answer and additionally I was looking on other forums as well to find out more. However I still cannot find a solution. Since I'm using mysqli_fetch_array the suggested answer really confuses me even further.

Answer 1

<?php
$inner_query = "SELECT * FROM additional_uploads";
$inner_result = mysqli_query($mysqli, $inner_query);
$rows = [];
while ($row = mysqli_fetch_array($inner_result)) {
$rows[$row['U_KEY']] .= $row['FILE_PATH'].",";
}
$sql = "SELECT * FROM test_users, image_uploads LIMIT 0, 27";
$result = mysqli_query($mysqli, $sql);
while($value = mysqli_fetch_array($result)) {
$files_key = $value["KEY"];
$allPaths = $rows[$files_key];
}
?>