Sum of unique customers in rolling trailing 30d window displayed by week - sql

Question

I'm working in SQL Workbench.
I'd like to track every time a unique customer clicks the new feature in trailing 30 days, displayed week over week. An example of the data output would be as follows:
Week 51: Reflects usage through the end of week 51 (Dec 20th) - 30 days. aka Nov 20-Dec 20th
Week 52: Reflects usage through the end of week 52 (Dec 31st) - 30 days. aka Dec 1 - Dec 31st.
Say there are 22MM unique customer clicks that occurred from Nov 20-Dec 20th. Week 51 data = 22MM.
Say there are 25MM unique customer clicks that occurred from Dec 1-Dec 31st. Week 52 data = 25MM. The customer uniqueness is only relevant to that particular week. Aka, if a customer clicks twice in Week 51 they're only counted once. If they click once in Week 51 and once in Week 52, they are counted once in each week.
Here is what I have so far:
select
min_e_date
,sum(count(*)) over (order by min_e_date rows between unbounded preceding and current row) as running_distinct_customers
from (select customer_id, min(DATE_TRUNC('week', event_date)) as min_e_date
from final
group by 1
) c
group by
min_e_date
I don't think a rolling count is the right way to go. As I add in additional parameters (country, subscription), the rolling count doesn't distinguish between them - the figures just get added to the prior row.
Any suggestions are appreciated!
edit Additional data below. Data collection begins on 11/23. No data precedes that date.

Answer 1

You can get the count of distinct customers per week like so:
select date_trunc('week', event_date) as week_start,
count(distinct customer_id) cnt
from final
group by 1
Now if you want a rolling sum of that count(say, the current week and the three preceding weeks), you can use window functions:
select date_trunc('week', event_date) as week_start,
count(distinct customer_id) cnt,
sum(count(distinct customer_id)) over(
order by date_trunc('week', event_date)
range between 3 week preceding and current row
) as rolling_cnt
from final
group by 1

Answer 2

Rolling distinct counts are quite difficult in RedShift. One method is a self-join and aggregation:
select t.date,
count(distinct case when tprev.date >= t.date - interval '6 day' then customer_id end) as trailing_7,
count(distinct customer_id) as trailing_30
from t join
t tprev
on tprev.date >= t.date - interval '29 day' and
tprev.date <= t.date
group by t.date;
If you can get this to work, you can just select every 7th row to get the weekly values.
EDIT:
An entirely different approach is to use aggregation and keep track of when customers enter and end time periods of being counted. This is a pain with two different time frames. Here is what it looks like for one.
The idea is to
Create an enter/exit record for each record being counted. The "exit" is n days after the enter.
Summarize these into periods of activity for each customer. So, there is one record with an enter and exit date. This is a type of gaps-and-islands problem.
Unpivot this result to count +1 for a customer being counted and -1 for a customer not being counted.
Do a cumulative sum of this count.
The code looks something like this:
with cd as (
select customer_id, date,
lead(date) over (partition by customer_id order by date) as next_date,
sum(sum(inc)) over (partition by customer_id order by date) as cnt
from ((select t.customer_id, t.date, 1 as inc
from t
) union all
(select t.customer_id, t.date + interval '7 day', -1
from t
)
) tt
),
cd2 as (
select customer_id, min(date) as enter_date, max(date) as exit_date
from (select cd.*,
sum(case when cnt = 0 then 1 else 0 end) over (partition by customer_id order by date) as grp
from (select cd.*,
lag(cnt) over (partition by customer_id order by date) as prev_cnt
from cd
) cd
) cd
group by customer_id, grp
having max(cnt) > 0
)
select dte, sum(sum(inc)) over (order by dte)
from ((select customer_id, enter_date as dte, 1 as inc
from cd2
) union all
(select customer_id, exit_date as dte, -1 as inc
from cd2
)
) cd2
group by dte;