code: def clean(self):
          
          if any(self.errors):
              # Don't bother validating the formset unless each form is valid on
              # its own
              return
          (selects, aliases, froms, wheres, sorts, groups_by,
           params) = self.get_query_parts()
          if not selects:
              validation_message = _(u"At least you must check a row to get.")
              raise forms.ValidationError(validation_message)
          self._selects = selects
          self._aliases = aliases
          self._froms = froms
          self._wheres = wheres
          self._sorts = sorts
          self._groups_by = groups_by
          self._params = params
docs: Checks that there is almost one field to select