Getting the right format of a .json file - php

Question

I'm working on implementing a chart from highcharts. The data needed in order for it to be displayed needs to be in the .json format.
It has the following scheme:
[
[
1167609600000,
21
]
]
I'm getting my data from a mysql database via a php script:
<?php
//OPEN CONNECTION TO DB
$connection = mysqli_connect('localhost','abc','def','ghi') or die("Error " . mysqli_error($connection));
//SELECT ROWS NEEDED
$sql = "SELECT test, temp FROM database";
$result = mysqli_query($connection, $sql) or die("Error in Selecting " . mysqli_error($connection));
//CONVERT MYSQL TO PHP ARR
$json_array= array();
while ($row= mysqli_fetch_assoc($result))
{
$json_array[]= $row;
}
//WRITE DATA TO FILE
$fp = fopen('temps.json', 'w');
fwrite($fp, json_encode($json_array, JSON_PRETTY_PRINT));
fclose($fp);
//DISCONNECT FROM DB
mysqli_close($connection);
?>
Now comes my problem. The data generated by my script looks like this:
[
{
"a": "2",
"price": "15"
}
]
Firstly, I dont know how to supress the column-name of every result in my sql query. Secondly, I dont get why my script creates curly brackets instead of square ones. And thirdly, why does it use "." for every value.
Anybody able to help me out?
Thank you

Answer 1

You push in your array an associative array, so the key are kept and are displayed in your JSON:
while ($row = mysqli_fetch_assoc($result))
{
$json_array[] = [ (int)$row['a'], (int)$row['price'] ];
}
Will outputs:
[
[
2,
15
]
]
Another way is to use array_values():
while ($row = mysqli_fetch_assoc($result))
{
$vals = array_values($row);
$vals = array_map('intval', $vals);
$json_array[] = $vals;
}