PHP print_r num_rows => 9 but blank page - php

Question

Previously I use the PHP file from my own hosting, but the problem occurred when I moved to my client's (GoDaddy).
I have two inputs - Automotive and Education (I have more but for this question, I just use two as example)
In my own, both input will print the output without problem. But in GoDaddy, only Education can produce output, while Automotive produce blank page. So I add this code:
echo '<pre>';
print_r($res);
echo '</pre>';
For input Automotive, I got:
<pre>mysqli_result Object
(
[current_field] => 0
[field_count] => 1
[lengths] =>
[num_rows] => 9
[type] => 0
)
</pre>
For input Edication, I got:
<pre>mysqli_result Object
(
[current_field] => 0
[field_count] => 1
[lengths] =>
[num_rows] => 4
[type] => 0
)
</pre>
[{"subcategory":"Adult & Continuing Education"},{"subcategory":"Early Childhood Education"},{"subcategory":"Educational Resources"},{"subcategory":"Other Educational"}]
What I have done so far:
Check the query - No problem. The query return the desired result in phpmyadmin
Increase memory limit - Done but in PHP setting, still stated as Default even after refresh the Dedicated IIS Application Pool
I have other input with its output/num rows more than 9 but it return the result without problem
PHP code:
<?php
if($_SERVER['REQUEST_METHOD']=='GET') {
require_once('dbConnect.php');
$category = $_GET['category'];
$sql = "SELECT subcategory FROM wg_categories WHERE category = '$category'";
$res = mysqli_query($con,$sql);
$result = array();
while($row = mysqli_fetch_array($res)){
array_push($result,
array('subcategory'=>$row[0]
));
}
echo json_encode($result);
mysqli_close($con);
}
?>
Is there something I have missed?
error_reporting - E_ALL
display_errors - on
log_errors - on

Answer 1

After reviewing php.net, the problem maybe at $row[0]. because the first element returned maybe $row[1]; to match the row id's in MySQL. So that maybe where the break is happening because it's accessing an element that may not exist.
http://php.net/manual/en/function.array.php
It may also be an issue with how MySQL is returning the array. Look at the below link for help, MySQLi driver maybe returning the array, as an Array of arrays or as an associative array, which is where the issue is coming from.
http://php.net/manual/en/mysqli-result.fetch-assoc.php
You may need to do the rows as associative. So using the actual column names. Like id, firstname, lastname etc. IE, $row['id']; $row['table_name'];
You may also want to try adding a try catch block, and then var dumping to see what is actually being returned or what everything looks like at that particular time. Then removing it once you have figured out what is going wrong.
http://php.net/manual/en/language.exceptions.php