Simple Window Function Solution in 1 Query
\nSELECT ROUND(\n    COUNT(DISTINCT player_id)/(SELECT COUNT(DISTINCT player_id) \n    FROM Activity),2\n) AS fraction\n\nFROM (\n    SELECT player_id,\n       
```\nSELECT ROUND(\n    COUNT(DISTINCT player_id)/(SELECT COUNT(DISTINCT player_id) \n    FROM Activity),2\n) AS fraction\n\nFROM (\n    SELECT player_id,\n           event_date,\n           MIN(event_date) OVER(PARTITION BY player_id) AS first_date\n    FROM Activity\n) sub\n\nWHERE DATEDIFF(event_date, sub.first_date) = 1\n```
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