if ( isset($start) ) {
          $params[':time_range_start'] = $start;
          $start_sql .= ' ((dtend IS NULL AND dtstart > :time_range_start) OR dtend > :time_range_start) ';
        }
        elseif ( isset($finish) ) {
          $params[':time_range_end'] = $finish;
          $finish_sql = ' dtstart < :time_range_end ';
        }
        if ( isset($start) || isset($finish) ) {
          $sql .= ' AND (rrule IS NOT NULL OR dtstart IS NULL OR (';
          if ( isset($start) ) $sql .= $start_sql;
          if ( isset($start) && isset($finish) ) $sql .= ' AND ';
          if ( isset($finish) ) $sql .= $finish_sql;
          $sql .= '))';
        }