build_target: only relating to a build target

      group: only relating to a (comps) group

      cg: only relating to a content generator

      """

      common_fields = {

          # fields:aliases common to all versioned tables

              if table not in table_fields:

                  raise koji.GenericError("No such history table: %s" % table)

      ret = {}

      for table in tables:

          fields = {}

          for field in common_fields:

              continue

          fields, aliases = zip(*fields.items())

          query = QueryProcessor(columns=fields, aliases=aliases, tables=[table],

          ret[table] = query.iterate()

      return ret