code: def columns(self, model=None):
          
          column = self.column(model=model)
          if column:
              yield column
  
          check = self.__value
          if not isinstance(check, (list, set, tuple)):
              check = (check,)
  
          for val in check:
              if isinstance(val, (Query, QueryCompound)):
                  for col in val.columns(model):
                      yield col
docs: Returns a generator that loops through the columns that are associated with this query.
          
          :return     <generator>(orb.Column)