Does not save the value and the Empty query error appears

If there is a value in the sql query, it does not take the value of the query in the variable $acd0

while (true) {
 $t= "SELECT MAX(id) AS id FROM accidente";

    $query2=mysqli_query($db,$t);
    while($acd=mysqli_fetch_array($query2))



$last= current($last_id);
//  $acd_1=current($acd);
 $ls=(( $last !== false) ? $last : ",  ");
//  $acd2=(( $acd_1 !== false) ? $acd_1 : ",  ");
                $valores3='("'.$acd[0].'","'.$ls.'"),';
                $valoresQ3= substr($valores3, 0, -1);


            $acd_impl=$db->query("INSERT INTO implicado_acd (id_acd, id_implicado) VALUES $valoresQ3");
            $sqlRess1=$db->query($acd_impl) or mysql_error();

    $last = next($last_id);
    //$acd_1= next($acd); 

    if($last === false) break;
          echo "string".$acd[0];             


    }   }