  select_union(THD *thd_arg):
    select_result_interceptor(thd_arg), write_err(0), table(0), records(0)
  { tmp_table_param.init(); }
  select_union(THD *thd_arg):
    select_result_interceptor(thd_arg), write_err(0), table(0), records(0)
  { tmp_table_param.init(); }