use left join
\nselect \nround(count(distinct b.player_id)/count(distinct a.player_id),2) as \'fraction\'\nfrom \n(select player_id, min(event_date) as event_date \nfrom acti
```\nselect \nround(count(distinct b.player_id)/count(distinct a.player_id),2) as \'fraction\'\nfrom \n(select player_id, min(event_date) as event_date \nfrom activity group by player_id) as a \nleft join activity as b on a.player_id = b.player_id \nand datediff(a.event_date, b.event_date) = -1\n```
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