PHP: displaying NULL but actually contains data

Question

product table structure is given below

    CREATE TABLE `products` (
  `id` int(6) unsigned NOT NULL AUTO_INCREMENT,
  `category_id` int(6) unsigned NOT NULL,
  `name` varchar(30) NOT NULL,
  `unit_id` int(6) unsigned NOT NULL,
  `brand_id` int(6) unsigned NOT NULL,
  `orignalCost` int(30) NOT NULL,
  `saleprice` int(30) NOT NULL,
  `deleted` tinyint(1) NOT NULL DEFAULT 0,
  PRIMARY KEY (`id`),
  KEY `fk-to-uom` (`unit_id`),
  KEY `fk-to-brand` (`brand_id`),
  KEY `category_id` (`category_id`),
  CONSTRAINT `fk-to-brand` FOREIGN KEY (`brand_id`) REFERENCES `brands` (`id`) ON DELETE CASCADE ON UPDATE CASCADE,
  CONSTRAINT `products_ibfk_1` FOREIGN KEY (`category_id`) REFERENCES `categories` (`id`) ON DELETE CASCADE ON UPDATE CASCADE
) ENGINE=InnoDB AUTO_INCREMENT=230 DEFAULT CHARSET=utf8mb4

Can someone please tell me what mistake i'm making as var_dump() displays the NUll values......is there any mistake in mysqli_fetch_array? it is showing like that "array(1) { [0]=> NULL } "

$selected_items_values = $_POST['product_id']; 
   $prices = [];
   foreach($selected_items_values as $prud)
   {
     if(isset($prud))
     {
      $priceSql = "SELECT saleprice from products where id = ' $prud ' ";
      $price=mysqli_query($db,$priceSql);
      $price = mysqli_fetch_array($price);
      array_push($prices , $price);
      var_dump($prices);

     } 
  }  

Answer 1

EDITED ANSWER

Here is sample table I've created. (I removed foreign keys)

CREATE TABLE `products` (
 `id` int(6) unsigned NOT NULL AUTO_INCREMENT,
 `category_id` int(6) unsigned NOT NULL,
 `name` varchar(30) COLLATE utf8_turkish_ci NOT NULL,
 `unit_id` int(6) unsigned NOT NULL,
 `brand_id` int(6) unsigned NOT NULL,
 `orignalCost` int(30) NOT NULL,
 `saleprice` int(30) NOT NULL,
 `deleted` tinyint(1) NOT NULL DEFAULT 0,
 PRIMARY KEY (`id`)
) 

Here is sample insert statements

INSERT INTO `products`VALUES (NULL, '1', 'name1', '1', '1', '100', '200', '0');
INSERT INTO `products`VALUES (NULL, '2', 'name2', '2', '2', '100', '200', '0');
INSERT INTO `products`VALUES (NULL, '3', 'name3', '3', '3', '100', '200', '0');
INSERT INTO `products`VALUES (NULL, '4', 'name4', '4', '4', '100', '200', '0');
INSERT INTO `products`VALUES (NULL, '5', 'name5', '5', '5', '100', '200', '0');
INSERT INTO `products`VALUES (NULL, '6', 'name6', '6', '6', '100', '200', '0');

Here is sample data I've entered.

+----+-------------+-------+---------+----------+-------------+-----------+---------+
| id | category_id |  name | unit_id | brand_id | orignalCost | saleprice | deleted |
+----+-------------+-------+---------+----------+-------------+-----------+---------+
|  1 |      1      | name1 |    1    |     1    |     100     |    200    |    0    |
+----+-------------+-------+---------+----------+-------------+-----------+---------+
|  2 |      2      | name2 |    2    |     2    |     100     |    200    |    0    |
+----+-------------+-------+---------+----------+-------------+-----------+---------+
|  3 |      3      | name3 |    3    |     3    |     100     |    200    |    0    |
+----+-------------+-------+---------+----------+-------------+-----------+---------+
|  4 |      4      | name4 |    4    |     4    |     100     |    200    |    0    |
+----+-------------+-------+---------+----------+-------------+-----------+---------+
|  5 |      5      | name5 |    5    |     5    |     100     |    200    |    0    |
+----+-------------+-------+---------+----------+-------------+-----------+---------+
|  6 |      6      | name6 |    6    |     6    |     100     |    200    |    0    |
+----+-------------+-------+---------+----------+-------------+-----------+---------+

Here is db connect get all data via PHP.

$conn = mysqli_connect("$db_host","$db_username","$db_pass","$db_name");
$query = $conn->query("SELECT * FROM `products`;");
var_dump($query);

Here is the result of above. You can see I have 6 rows.

mysqli_result Object
(
    [current_field] => 0
    [field_count] => 8
    [lengths] => 
    [num_rows] => 6
    [type] => 0
)

In order to loop through php object use foreach

foreach ($query as $key => $value) {
  var_dump($value);
}

Foreach result goes like

Array
(
    [id] => 1
    [category_id] => 1
    [name] => name1
    [unit_id] => 1
    [brand_id] => 1
    [orignalCost] => 100
    [saleprice] => 200
    [deleted] => 0
)

Array
(
    [id] => 2
    [category_id] => 2
    [name] => name2
    [unit_id] => 2
    [brand_id] => 2
    [orignalCost] => 100
    [saleprice] => 200
    [deleted] => 0
)

It continues like that...

In order to get only saleprice use it like below.

foreach ($query as $key => $value) {
  var_dump($value['saleprice']);
}

So this is how you can get. Rest of it up to you whatever you want to do with it.