About combining multiple incoming variables with PHP

I want to combine the values ​​I pulled from the database with foreach and assign them to a single variable. but I get an error output even though I think I did it without any problems.

(I am changing the table names for security reasons.)

    <?php 
// example user
$user_id= "1";

$query = $db->query("SELECT tmp.* FROM (SELECT * FROM `statistics_tables`WHERE `user`='".$user_id."' ORDER BY id DESC LIMIT 20 ) tmp ORDER BY tmp.id ASC;");

foreach($query as $row) {

    $download .= $row["download"].',';

} 

echo $download;
?>

error in picture

$download .= $row["download"].’,’;

seems to be happening on the line

>Solution :

Try:

$download = [];

foreach($query as $row) {

    $download[] = $row["download"];

}

echo implode(',', $download);