oracle solution
\n\n# Code\n\nselect round(count(a.player_id)/count(b.player_id),2) as fraction \nfrom activity a right join activity b\non a.player_id = b.player_id\nand a.eve
\n\n# Code\n```\nselect round(count(a.player_id)/count(b.player_id),2) as fraction \nfrom activity a right join activity b\non a.player_id = b.player_id\nand a.event_date = b.event_date +1\nwhere ( b.player_id , b.event_date )in (select  player_id , min(event_date)  from activity  group by player_id) \n```
['Oracle']