class mysql_db {
    private static $instance;
    public static $connection;

    public function __construct($host=null, $user=null, $password=null, $db=null) {
        if(!self::$instance && !$host) {
            throw new Exception("Missing Database..!!!");
        }
        self::$connection = mysqli_connect($host,$user,$password,$db);
    }

    public function __destruct() {
        mysqli_close(self::$connection);
    }

    public function getData($table_name) {
        $rs= mysqli_query(self::$connection,"SELECT * FROM $table_name");
        return mysqli_fetch_all($rs,MYSQLI_ASSOC);
    }

    public function getOne($table_name) {
        $rss= mysqli_query(self::$connection,"SELECT * FROM $table_name LIMIT 1");
        return mysqli_fetch_assoc($rss);
    }

    public function find($table_name,$sn,$val) {
        $rq= mysqli_query(self::$connection,"SELECT * FROM $table_name WHERE $sn='$val'");
        return mysqli_fetch_all($rq,MYSQLI_ASSOC);
    }


**//   I AM GETTING ERROR FROM THESE LINES**

//->    public function __call($table_name,$sn) {
//->        //var_dump("SELECT * FROM $table_name where sn='1'");
//->        $rt= mysqli_query(self::$connection,"SELECT * FROM $table_name
            WHERE '$sn'")or die(mysqli_error()) ;
//->        return mysqli_fetch_all($rt,MYSQLI_ASSOC);
    }

    public static function getInstance() {
        try {
            if(!self::$instance) {
                self::$instance=new static('localhost','root','','xam');
            }
        } catch(Exception $e) {
            echo 'Caught Error: ', $e->getMessage(), "n";
        }
        return self::$instance;
    }
}
$h= mysql_db::getInstance();
var_dump($h->name("1"));