$table_prefix="tbl1";
$username="ghost";
$password="!@#$%^&*(";
$res = $modx->db->select("id", $table_prefix."_web_users",
"username='$username' AND password='".$password."'");
$tbl1=$modx->getFullTablename('web_users');
$tbl2=$modx->getFullTablename('web_user_attributes');
$sql = "SELECT wu.*, wua.fullname
FROM $tbl1 wu
INNER JOIN $tbl2 wua ON wua.internalkey=wu.id
WHERE "username='$username' AND password='".$password."'";
$res = $modx->db->query($sql);
$rows = $modx->db->makeArray($res);