$w=$mysqli->query($sql);

 $db = new mysqli('localhost', 'root', '', 'w');
 if($db->connect_error){
     die('Connect Error ( '.$db->connect_errno.' )'.$db->connect_error);
 }
 echo 'Connect OK.<br>';
 $wtab = 'w'.rand(123,987);
 $w = $db->query("CREATE TABLE $wtab (w int)");
 var_dump($w);
 $w = $db->query("INSERT INTO $wtab VALUES(123)");
 var_dump($w);
 $w = $db->query("SELECT * FROM $wtab");
 var_dump($w);

Connect OK.
D:\wamp64\www\wdb.php:21:boolean false
D:\wamp64\www\wdb.php:23:boolean true
D:\wamp64\www\wdb.php:25:
object(mysqli_result)[3]
  public 'current_field' => int 0
  public 'field_count' => int 1
  public 'lengths' => null
  public 'num_rows' => int 2
  public 'type' => int 0