SIMPLE SOLUTION with ONLY 1 'join'
\nselect round(count(distinct a.player_id)/(select count(distinct player_id) from Activity),2) fraction\nfrom \n(   #First select first login rows for each of t
```\nselect round(count(distinct a.player_id)/(select count(distinct player_id) from Activity),2) fraction\nfrom \n(   #First select first login rows for each of the players\n    select player_id, min(event_date) first_date from Activity group by player_id\n\t#Then join with the original Activity table on the following conditions\n) a join Activity a1 on a.first_date +1 = a1.event_date and a.player_id = a1.player_id\n```
['MySQL']