message: timestamp bug
diff: @@ -1485,6 +1485,11 @@ class ExploreMixin: # pylint: disable=too-many-public-methods
  # if groupby field/expr equals granularity field/expr
  if selected == granularity:
  table_col = columns_by_name[selected]
  + if isinstance(table_col, dict):
  + outer = self.get_timestamp_expression(
  + table_col, time_grain, selected, template_processor
  + )
  + else:
  outer = table_col.get_timestamp_expression(
  time_grain=time_grain,
  label=selected,
  