cioè così non si può scrivere..ma avrei bisogno una cosa del genere

$azienda = $_SESSION["azienda"];
$username = $_SESSION["username"];
$password = $_SESSION["password"];

$paramx = "SELECT azienda FROM users WHERE username='$username' AND password='$password'";

$sql = "SELECT markers.id, DATE_FORMAT(markers.ts,'%e-%c-%Y %h:%i %p') AS ts, markers.addresstre, markers.addressquattro, markers.addresscinque, markers.addresssei, markers.azienda, comments.idcomment, comments.comment FROM markers LEFT JOIN comments ON markers.id = comments.idcomment WHERE markers.azienda = '$paramx' ORDER BY markers.ts DESC";