// 设置表前缀为空
        $this->db->set_dbprefix('');

        $catid = $cxdata['catid'];
        $qishu = $cxdata['qishu'];
        $count = $this->db->query("select id from tablename where catid='$catid' and qishu='$qishu'")->row();
        if(0 == (int)$count->id){
            // 不存在则添加
            $this->db->insert('tablename ', $cxdata);
        }else{
            // 存在则修改
            $this->db->where('id', $count->id)->update('tablename ', $cxdata);
        }
        // 表前缀更改回来，以免出错
        $this->db->set_dbprefix('pre_');