SQL请求位于函数内部时发生致命错误

Question

此代码给出了错误。

  <?php
    class DbOperation
    {
        private $con;
        function __construct()
        {
            require_once dirname(__FILE__) . '/DbConnect.php';
            $db = new DbConnect();
            $this->con = $db->connect();
        }
        function UyingaKirish($data){
            function Tekshir($ki1){

                $stmt2=$this->con->prepare("SELECT HowManyPlayers FROM groups WHERE NumberOfGroup=?"); //error is here
                $stmt2->bind_param("i",$ki1);
                $stmt2->execute();
                $stmt2->store_result();
                return $ki1;
            }

$u=Tekshir(5);
    }

但是当我这样使用时，效果很好

class DbOperation
    {
        private $con;
        function __construct()
        {
            require_once dirname(__FILE__) . '/DbConnect.php';
            $db = new DbConnect();
            $this->con = $db->connect();
        }
        function UyingaKirish($data){
   $u=5;
                $stmt2=$this->con->prepare("SELECT HowManyPlayers FROM groups WHERE NumberOfGroup=?");
                $stmt2->bind_param("i",$u);
                $stmt2->execute();
                $stmt2->store_result();
    }

所以整个错误是

  

致命错误，当不在对象上下文中时使用$ this

如何在函数内部使用它？