Вывод из mysql данных в переменную

$reg = mysqli_query($link, "SELECT * FROM `table` WHERE `id` > '0'"); 
while ($reg2 = mysqli_fetch_object($reg)) { 
$reg_online = "{$reg2->id}, "; 
echo "$reg_online"; 
}

$str.=$val;

$arr[]=$val;

$str='';

$arr=[]; // $arr=array();

 $link = mysqli_connect("localhost", "user", "pass", "db");
        mysqli_select_db("db", $link);
 
        $reg = mysqli_query($link, "SELECT * FROM `chat` WHERE `id` > '0'");    
        while ($reg2 = mysqli_fetch_object($reg)) {
        $reg_online = "{$reg2->id}, ";
        echo "$reg_online";
        }
        $peremennaya .= $reg_online;
        echo $peremennaya;
        
        mysqli_close($link);

        $str = '';
        $reg = mysqli_query($link, "SELECT * FROM `chat` WHERE `vk_id` > '0'");    
        while ($reg2 = mysqli_fetch_object($reg)) {
        $reg_online = "{$reg2->vk_id}, ";
        echo "$reg_online";
        $str.= $reg_online;
        }
        echo "<br>";
        $peremennaya .= $str;
        echo $peremennaya;
 
        mysqli_close($link);

echo '<br>',$str;