mysql - very simple solution
\nwith cte as (select player_id, min(event_date) over(partition by player_id) + 1= event_date as is_return from activity)\nselect round(sum(is_return)/count(dis
```\nwith cte as (select player_id, min(event_date) over(partition by player_id) + 1= event_date as is_return from activity)\nselect round(sum(is_return)/count(distinct player_id), 2)  as fraction from cte\n```
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