求TP大神帮小弟我看看，为什么不能验证登陆

     
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[code=javascript]

 //登陆验证
   public function doLogin()
   {
   	$username=$_GET['username'];
   	$password=$_GET['password'];
   	$user=M('member');
   	$where['username']=$username;
   	$where['password']=md5($password);
   	$count=$user->where($where)->count();
   	if($count)
   	{
   		$_SESSION['username']=$username;
   		echo '验证成功';
   	}
   	else
   	{
   		echo '验证失败';
   	}
   }