- var_dump: documentation ( source)
- array_diff_ukey: documentation ( source)
<?php
echo 'Hello World';
$sql = [1 => ["id" => 1, "num" => "123"], 2 => ["id" => 2, "num" => "456"]];
$mongo = ["id" => 1, "num" => "123"];
array_diff_ukey ($mongo, $sql, function($item) {return $item['num'];} );
var_dump($a);