Codeigniter with big database

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My Function get navigation

Code:

public function get_navigation_header(){
    $result = array();
    $result = $this->array_category();
    foreach($result as $key=>$val){
        $result[$key]['submenu'] = $this->array_category($result[$key]['id']);
        $result[$key]['news'] = $this->hotnew_category($result[$key]['id']);
    }
    return $result;
}

Get news in here

Code:

$result[$key]['news'] = $this->hotnew_category($result[$key]['id']);

This is function get news

Code:

public function hotnew_category($id){
    $this->db->select('id,name,image,created,content,summary');
    $this->db->limit(3);
    $this->db->where('cat',$id);
    $this->db->order_by('created','DESC');
    $data = $this->db->get(TABN);
    $news = $data->result_array();
    foreach($news as $key=>$val){
        $news[$key]['link'] = $this->linkNew($news[$key]['id']);
        $news[$key]['image'] = $this->tungphut->get_image_instead($news[$key]['image'],$news[$key]['content']);
    }
    return $news;
}

This is function get link for a new

Code:

public function linkNew($id){
    $this->db->select('id,cat,rewrite');
    $this->db->where('id',$id);
    $data = $this->db->get(TABN);
    $new = $data->row_array();
    $url = $new['rewrite'].'.html';
    $this->db->where('id',$new['cat']);
    $data = $this->db->get(TABCAT);
    $category = $data->row_array();
    $url = $this->hasParent($category['parent'],$category['rewrite']).$url;
    $url = base_url($url);
    return $url;
}
public function hasParent($parent,$rewrite){
    $url = '';
    if($parent == 0){
        $url = $rewrite.'/';
    }
    else {
        $this->db->where('id',$parent);
        $data = $this->db->get(TABCAT);
        $category = $data->row_array();
        $url = $this->hasParent($category['parent'],$category['rewrite']).$rewrite.'/';
    }
    return $url;
}