[SQL문제풀기] Unique Users Per Client Per Month

문제

StrataScratch - Unique Users Per Client Per Month

StrataScratch

https://platform.stratascratch.com/coding/2024-unique-users-per-client-per-month?code_type=1

내가 작성한 정답

MySQL

select client_id, month(time_id) as month, count(distinct user_id) as users_num
from fact_events
group by client_id, month(time_id)
order by 1, 2;

PostgreSQL, Oracle

select client_id, extract(month from time_id) as month, count(distinct user_id) as users_num
from fact_events
group by client_id, extract(month from time_id)
order by 1, 2;

select client_id, to_number(to_char(time_id,'mm'),'99') as month, count(distinct user_id) as users_num
from fact_events
group by client_id, to_number(to_char(time_id,'mm'),'99')
order by 1, 2;