php mysql数据库操作分页类

                $this->sql = "SELECT ".$this->table["fileds"]." FROM `".$this->table["tablename"]."` ".($this->table["where"]!=""?" WHERE ".$this->table["where"].' AND '.$this->table["id"].'>=':' WHERE '.$this->table["id"].'>=').'(SELECT '.$this->table["id"].' FROM `'.$this->table["tablename"].'` ORDER BY '.$this->table["id"].' LIMIT '.$this->page_size*($this->page-1).', 1)'." ORDER BY ".$this->table["orderby"]." ".$this->table["descasc"]." LIMIT ".$this->page_size;
            }else{
                $this->sql = "SELECT ".$this->table["fileds"]." FROM `".$this->table["tablename"]."` ".($this->table["where"]!=""?" WHERE ".$this->table["where"]:"")." ORDER BY ".$this->table["orderby"]." ".$this->table["descasc"]." LIMIT ".$this->page_size*($this->page-1).", ".$this->page_size;
            }
            //SELECT * FROM articles ORDER BY id DESC LIMIT 0, 20
            //SELECT * FROM articles WHERE category_id = 123 AND id >= (SELECT id FROM articles ORDER BY id LIMIT 10000, 1) LIMIT 10
            return $this->sql;        //SQL语句
        }
        function set_url(){
            $arr_url = array();
            parse_str($_SERVER["QUERY_STRING"], $arr_url);
            unset($arr_url["page"]);
            if (empty($arr_url)){
                $str = "page=";
            }else{
                $str = http_build_query($arr_url)."&page=";
            }
            $this->url = "http://".$_SERVER["HTTP_HOST"].$_SERVER["PHP_SELF"]."?".$str;