ClickHouse net dollar retention

ch-ndr.sql

with tbl as (
-- fake table
select c1 as usr, c2 as price, c3 as d from VALUES (
	('a', 10, toDate('2023-08-09'))
	, ('a', 10, toDate('2023-08-10'))
	, ('a', 8, toDate('2023-08-11'))
	, ('a', 11, toDate('2023-08-12'))
	, ('a', 12, toDate('2023-08-13'))
	, ('b', 10, toDate('2023-08-09'))
	, ('b', 10, toDate('2023-08-10'))
	, ('b', 9, toDate('2023-08-11'))
	, ('b', 11, toDate('2023-08-12'))
	, ('b', 12, toDate('2023-08-13'))
	, ('c', 11, toDate('2023-08-11'))
	, ('c', 11, toDate('2023-08-12'))
	, ('c', 15, toDate('2023-08-13'))
	, ('c', 15, toDate('2023-08-15')) -- a non-contig day
)
)
, mins as (
-- get the first date and price we saw them at (aggregate down if needed)
select usr, min(d) as first_d
from tbl
group by usr
order by usr asc
)
, buckets as (
-- aggregate the days based on the delta to the first date
select usr, sum(price) as price, mins.first_d, dateDiff('day', mins.first_d, d) as delta
from tbl
left join mins on mins.usr = tbl.usr
group by usr, delta, mins.first_d
)
, first_deltas as (
select usr, argMin(price, delta) as first_delta_price
from buckets
group by usr
)
-- select * from first_deltas;
, per_user as (
-- get each user's ndr
select buckets.usr as usr
, mins.first_d as start
, delta
, price/first_deltas.first_delta_price as ndr -- could do multiple quantiles here, etc.
from buckets
left join mins on mins.usr = buckets.usr
left join first_deltas on first_deltas.usr = buckets.usr
order by buckets.usr asc, start asc, delta asc with fill
)
-- select * from per_user;
, aggs as (
-- get the average ndr for each start date
-- could use this as final select to have tabular format
select
start -- could do toStartOfInterval here since that only changes the shown start, but not the deltas
, delta
-- , uniq(if(ndr = 0, null, usr)) as users -- don't count the user if they didn't do anything this delta
, uniq(usr) as users -- count them regardless of whether the earned anything
, round(avg(ndr), 2) as ndr_a
from per_user
group by start, delta
order by start asc, delta asc
)
-- select * from aggs;
-- group up in arrays for each start date
select start, groupArray(ndr_a) as ndr_a, groupArray(users) as users_a, groupArray(delta) as delta_a
from aggs
group by start
;

Note that ndr_a and users drop together (e.g. if a user does not do anything in an interval than the avg goes down) because a user still impacts the average for that cohort (start date). The reason to drop the user number is because that is the users that had something in that delta, not the number of users that were considered when calculating the avg.