code: def _queryContainer(self, store):
          
          if self._subselectSQL is None:
              sql, args = self.container._sqlAndArgs('SELECT',
                                                     self.container._queryTarget)
              self._subselectSQL, self._subselectArgs = sql, args
          return self._subselectSQL
docs: Generate and cache the subselect SQL and its arguments.  Return the
          subselect SQL.