如何从mysqli中获取json对象/数组（所有匹配的行）没有索引

i spent lot of hours trying to figure out the right way to output json array/object from mysql database like this :

expected output 
    {
        "ITEM1": 20,
        "ITEM2": 15,
        "ITEM3": 12
    }

As each key/value pair corresponding to one mysql table row (no need to display ID column).

id |item| price

This is my current code using MYSQLND driver on debian:

<?php
header('Content-Type: application/json');

$servername = "localhost";
$username = "root";
$password = "pswd";
$dbname = "json";


$conn = new mysqli($servername, $username, $password, $dbname);

if ($conn->connect_error) {
    die("Connection failed: " . $conn->connect_error);
}


$itemInitArr = array();
$decharge = 0;
$stmt = $conn->prepare("SELECT item, price FROM stock WHERE total_sold = ?");
$stmt->bind_param("i", $decharge);
$stmt->execute();
$result = $stmt->get_result();


                            while ($itemInit = $result->fetch_assoc())
                            {
                                $itemInitArr[] = array (
                                            $itemInit['item'] => $itemInit['price']
                                    );
                            }
$stmt->close();                         
$final_data = json_encode($itemInitArr, JSON_PRETTY_PRINT); 
echo $final_data;

$conn->close();
?>

which output this :

[
    {
        "ITEM1": 20
    },
    {
        "ITEM2": 15
    },
    {
        "ITEM3": 12
    }
]

So, where is the mistake and how to solve it to match expected output ?

If you change the way you build your array to...

$itemInitArr[$itemInit['item']] =  $itemInit['price'];

try using

$idx = 1; 
while ($itemInit = $result->fetch_assoc()){
     $itemInitArr['ITEM'.$idx] =  $itemInit['price'];
     $idx++;
}
$final_data = json_encode($itemInitArr, JSON_PRETTY_PRINT); 

of if the ITEM1 ... ITEMN is the content fo the column item

     $itemInitArr[$itemInit['item']] =  $itemInit['price'];

  <?php
header('Content-Type: application/json');

$servername = "localhost";
$username = "root";
$password = "pswd";
$dbname = "json";


$conn = new mysqli($servername, $username, $password, $dbname);

if ($conn->connect_error) {
    die("Connection failed: " . $conn->connect_error);
}


$itemInitArr = array();
$decharge = 0;
$stmt = $conn->prepare("SELECT item, price FROM stock WHERE total_sold = ?");
$stmt->bind_param("i", $decharge);
$stmt->execute();
$result = $stmt->get_result();


                            while ($itemInit = $result->fetch_assoc())
                            {
                                $itemInitArr[$itemInit['item']] = $itemInit['price'];

                            }
$stmt->close();                         
$final_data = json_encode($itemInitArr, JSON_PRETTY_PRINT); 
echo $final_data;

$conn->close();
?>