我试图截断一个表，但是为什么它不起作用？数据库查询中一定有问题吗？

$sql = "TRUNCATE TABLE `table_name`";

$result = $connection -> query($sql);

理想情况下，我想一次性截断所有表-有可能吗？

如果您想知道我用来进行数据库查询的类的内容是什么，

#connects the database and handling the result
class __database {

 protected $connection = null;
 protected $error = null;

 #make a connection
 public function __construct($hostname,$username,$password,$database)
 {
  $this -> connection = new mysqli($hostname,$username,$password,$database);

  if (mysqli_connect_errno()) 
  {
   printf("Connect failed: %s\n", mysqli_connect_error());
   exit();
  }
 }

 ...

 #performs a query on the database
 public function query($query)
 {
  $result = $this -> connection -> query($query); 
  if($result) 
  {
   return $result;
  } 
  else
  {
   $this -> error = $this -> connection -> error;
   return false;
  }

 }


 #display error
 public function get_error() 
 {
  return $this -> error;
 }

 #closes the database connection when object is destroyed.
    public function __destruct()
    {
        $this -> connection -> close();
    }
}

谢谢。

编辑：

下面是我如何调用db对象，

# the host used to access DB
define('DB_HOST', 'localhost');

# the username used to access DB
define('DB_USER', 'root');

# the password for the username
define('DB_PASS', 'xxx');

# the name of your databse 
define('DB_NAME', 'xxx');

$connection = new __database(DB_HOST,DB_USER,DB_PASS,DB_NAME);