
5. Which nation has participated in all of the olympic games
      with tot_games as
              (select count(distinct games) as total_games
              from olympics_history),
          countries as
              (select games, nr.region as country
              from olympics_history oh
              join olympics_history_noc_regions nr ON nr.noc=oh.noc
              group by games, nr.region),
          countries_participated as
              (select country, count(1) as total_participated_games
              from countries
              group by country)
      select cp.*
      from countries_participated cp
      join tot_games tg on tg.total_games = cp.total_participated_games
      order by 1;
