How to Insert a JSON code with PHP & SQL? - php

Question

I am trying to Insert my Categories SQL tables with a JSON in the below format.
[
{"id":21, "children": [{"id":4},{"id":7}]},
{"id":6},
{"id":5},
{"id":20},
{"id":10},
{"id":9}
]
I have tried to make it possible with this Code:
if(isset($_POST['category'])){
if(in_array($_GET['key'], $_SESSION['key'])){
unset($_SESSION['key'][array_search($_GET['key'], $_SESSION['key'])]);
$i = 1;
$rootof = array();
foreach($_POST['category'] as $cat => $parent){
if($parent == 'children'){
$p = "NULL";
$root = "NULL";
}else{
$p = intval($parent);
if(isset($rootof[$p])){
$root = $rootof[$p];
$rootof[intval($cat)] = $rootof[$p];
}else{
$root = $p;
$rootof[intval($cat)] = $p;
}
}
mysqli_query($db, "UPDATE ads_categories SET category_order = $i, category_parent = $p, category_root = $root WHERE category_id = ".intval($cat));
$i++;
}
echo 'Success';
}else{
echo 'Error';
}
}
I expect Saving the Categories by Id and subcategories (children) to Database.
I want to Insert Id 21, 6, 5 to categories->id,
if array has Children it means that it has subcategories.
subcategories has category_parent id to main category
Example: Categorie ID 4 category_parent would be 21