1.游戏玩法分析IV

AC:

select IFNULL(round(count(distinct(Result.player_id)) / count(distinct(Activity.player_id)), 2), 0) as fraction
from (
  select Activity.player_id as player_id
  from (
    select player_id, DATE_ADD(MIN(event_date), INTERVAL 1 DAY) as second_date
    from Activity
    group by player_id
  ) as Expected, Activity
  where Activity.event_date = Expected.second_date and Activity.player_id = Expected.player_id
) as Result, Activity

2.