我在mysql查询中有IS NULL字如何删除IS NULL

Question

我在我的codeigniter视图页面中添加了分页但我在我的sql查询中有了problam。在查询中我有IS NULL字 所以我想删除IS NULL字。

这是我的控制器功能

function category()
{
    $this->load->model('news_model');
    $this->load->model('get_db');
    $cat =  $this->uri->segment(2);

      $cat_id = $cat;

     $data['current_category']=$cat_id;

     $config['per_page'] = 6;



    $config['base_url'] = base_url().'category/'.$cat_id;

    $config['use_page_numbers'] = TRUE;

    $config['num_links'] = 5;

    $config['full_tag_open'] = '<ul>';

    $config['full_tag_close'] = '</ul>';

    $config['num_tag_open'] = '<li>';

    $config['num_tag_close'] = '</li>';

    $config['cur_tag_open'] = '<li class="active"><a>';

    $config['cur_tag_close'] = '</a></li>';

     $page = $this->uri->segment(3);

    $data['page_no']=$page;

      $limit_end = ($page * $config['per_page']) - $config['per_page'];


        if ($limit_end < 0){

             $limit_end = 0;

        } 
    $data['count_news']= $this->news_model->count_news($cat_id);

    $data['news'] = $this->news_model->viewnews($cat_id,$config['per_page'],$limit_end);
    $config['total_rows'] = $data['count_news'];

     $this->pagination->initialize($config);   

    $data['random_post'] = $this->news_model->get_randompost();
    $data['footer_recent'] = $this->news_model->get_footer_recent();
    $data['category'] = $this->get_db->get_category();
    $this->load->view('header',$data);
    $this->load->view('category',$data);
    $this->load->view('footer');
}

这是我的模特功能

function viewnews($id,$limit_start=null,$limit_end=null)
{   
    $this->db->select('*');

    $this->db->from('add_news');
    $where = "FIND_IN_SET($id,type)";
    $this->db->where($where);
    $this->db->order_by('id','DESC');

    if($limit_start && $limit_end){

      $this->db->limit($limit_start, $limit_end);   

    }
    if($limit_start != null){

      $this->db->limit($limit_start, $limit_end);    

    }
    $query = $this->db->get();

    print_r($this->db->last_query());
    die;
    return $query->result_array();  
}

然后我有了这个查询

SELECT * FROM (`add_news`) WHERE FIND_IN_SET(4,type) IS NULL ORDER BY `id` DESC LIMIT 6

请删除IS NULL字

请帮助......