Вася Борисевич

$sth1 = $mysqli->query("SELECT * FROM `tab1`");
$sth2 = $mysqli->query("SELECT * FROM `tab2`");

$arr1 = $sth1->fetch_all(MYSQLI_ASSOC);
$arr2 = $sth2->fetch_all(MYSQLI_ASSOC);

$arr  = array_merge($arr1, $arr2);

foreach ( $arr as $key => $row ) {
	$art[$key] = $row['date_create'];
}

array_multisort($art, SORT_ASC, $arr);