Faster than 95%
select round(sum(res)/count(distinct player_id),2) as fraction from\n(select if(datediff(b.event_date,a.event_date) = 1,1,0) as res, \na.player_id from\n(select
select round(sum(res)/count(distinct player_id),2) as fraction from\n(select if(datediff(b.event_date,a.event_date) = 1,1,0) as res, \na.player_id from\n(select player_id, min(event_date) as event_date from activity group by player_id) as a\nleft join activity b on a.player_id = b.player_id )c\n
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