- var_dump: documentation ( source)
- array_diff: documentation ( source)
<?php
$sql = [1 => ["id" => 1, "num" => "123"], 2 => ["id" => 2, "num" => "456"]];
$mongo = ["id" => 1, "num" => "123"];
$mongo = array($mongo);
var_dump(is_array($sql), is_array($mongo));
array_diff($sql, $mongo);