Tarex

<?php
$data = ['key1' => ['key2' => ['key3' => 123]]];

$keys = 'key1.key2.key3';
$keysArray = explode('.', $keys);

$element = &$data;
foreach ($keysArray as $key) {
    $element = &$element[$key];
}
$element = 321;

<?php 
if ($_GET['date']):
    $sort1 = $pdo->prepare("SELECT * FROM video ORDER BY date_format DESC");
    $sotr1->execute();
    $mov = $sort1->fetchAll();