13.1 day retention 3 (2 subset)


#1

what's wrong in here?
select
date(g1.created_at) as dt,
count(distinct g1.user_id) as total_users,
count(distinct g2.user_id) as retained_users
from gameplays as g1
join gameplays as g2 on
g1.user_id = g2.user_id
and date(g1.created_at) = date(datetime(g2.created_at, '-1 day'))
group by 1
order by 1
limit 100;


#2

@objectjumper37873,
They are asking you to LEFT JOIN

have a look at the pictures,
so you can get a better feeling on what you are achieving with your SELECT.
= http://stackoverflow.com/questions/565620/difference-between-join-and-inner-join29
= http://stackoverflow.com/questions/448023/what-is-the-difference-between-left-right-outer-and-inner-joins?sort=newest%3E13