- Output for 8.1.0 - 8.1.28, 8.2.0 - 8.2.19, 8.3.0 - 8.3.7
- array ( 0 => 1, 1 => 2, )
<?php
$array = [
['projects_users' => ['project_id' => 1]],
['projects_users' => ['project_id' => 2]],
];
var_export(array_column(array_column($array, 'projects_users'), 'project_id'));