docs: def bind(self, cube):
          """ When one column needs to match, use the key. """
          if self.measure:
              table, column = self.measure.bind(cube)
          else:
              table, column = cube.fact_table, cube.fact_pk
          # apply the SQL aggregation function:
          column = getattr(func, self.function)(column)
          column = column.label(self.ref)
          column.quote = True
          return table, column