代码点火器从数据库分页限制，偏移量

我在CI 3.0中启动了一个web应用程序，一切都很顺利，我的分页工作正常，但有一个问题我无法解决。。。

例如，我有以下URL：localhost/statistics/api_based导航时，将显示$query结果，并生成链接，确定。但是，例如，当我导航到第2页时，URL将变为：localhost/sttatistics/dll_based/index/2和第3页将变为host/sttatistics/api_based/index.3，因此我使用段。现在的问题是生成的查询：

SELECT * FROM `shield_api` ORDER BY `id` ASC limit 20 offset 2

偏移量2-是页码2，如果我是正确的，它应该是20。我每页显示20个结果，所以第一页正确地显示了1-20的结果，但第二页将显示2-21的结果，所以你明白我的意思，这不好…

这是我的控制器：

function index($offset = 0) {
        // Enable SSL?
        maintain_ssl ( $this->config->item ( "ssl_enabled" ) );
        // Redirect unauthenticated users to signin page
        if (! $this->authentication->is_signed_in ()) {
            redirect ( 'account/sign_in/?continue=' . urlencode ( base_url () . 'statistics/api_based' ) );
        }
        if ($this->authentication->is_signed_in ()) {
            $data ['account'] = $this->account_model->get_by_id ( $this->session->userdata ( 'account_id' ) );
        }
        $per_page = 20;
        $qry = "SELECT * FROM `shield_api` ORDER BY `id` ASC";
        //$offset = ($this->uri->segment ( 4 ) != '' ? $this->uri->segment ( 4 ) : 0);
        $config ['total_rows'] = $this->db->query ( $qry )->num_rows ();
        $config ['per_page'] = $per_page;
        $config ['uri_segment'] = 4;
        $config ['base_url'] = base_url () . '/statistics/api_based/index';
        $config ['use_page_numbers'] = TRUE;
        $config ['page_query_string'] = FALSE;
        $config ['full_tag_open'] = '<ul class="pagination">';
        $config ['full_tag_close'] = '</ul>';
        $config ['prev_link'] = '&laquo;';
        $config ['prev_tag_open'] = '<li>';
        $config ['prev_tag_close'] = '</li>';
        $config ['next_link'] = '&raquo;';
        $config ['next_tag_open'] = '<li>';
        $config ['next_tag_close'] = '</li>';
        $config ['cur_tag_open'] = '<li class="active"><a href="#">';
        $config ['cur_tag_close'] = '</a></li>';
        $config ['num_tag_open'] = '<li>';
        $config ['num_tag_close'] = '</li>';
        $config ["num_links"] = round ( $config ["total_rows"] / $config ["per_page"] );
        $this->pagination->initialize ( $config );
        $data ['pagination_links'] = $this->pagination->create_links ();
        //$data ['per_page'] = $this->uri->segment ( 4 );
        $data ['offset'] = $offset;
        $qry .= " limit {$per_page} offset {$offset} ";
        if ($data ['pagination_links'] != '') {
            $data ['pagermessage'] = 'Showing ' . ((($this->pagination->cur_page - 1) * $this->pagination->per_page) + 1) . ' to ' . ($this->pagination->cur_page * $this->pagination->per_page) . ' results, of ' . $this->pagination->total_rows;
        }
        $data ['result'] = $this->db->query ( $qry )->result_array ();
        $this->load->view ( 'statistics/api_based', isset ( $data ) ? $data : NULL );
    }

有人能给我指一下我的问题吗？任何帮助都是值得的。