public function inner_where($value = false)
    {
        if ($value !== false)
        {
            $this->inner_value = $value;
        }
        // nested table connection
        if ($this->is_inner && $this->inner_where)
        {
            $field = reset($this->inner_where);
            $this->where_pri($field, $this->inner_value, 'AND', 'nstd_tbl');
            $this->pass_default($field, $this->inner_value);
        }
    }