
7. Which Sports were just played only once in the olympics.
      with t1 as
          	(select distinct games, sport
          	from olympics_history),
          t2 as
          	(select sport, count(1) as no_of_games
          	from t1
          	group by sport)
      select t2.*, t1.games
      from t2
      join t1 on t1.sport = t2.sport
      where t2.no_of_games = 1
      order by t1.sport;
