Display COUNT(*) for every week instead of every day - sql

Question

Let us say that I have a table with user_id of Int32 type and login_time as DateTime in UTC format. user_id is not unique, so SELECT user_id, login_time FROM some_table; gives following result:
┌─user_id─┬──login_time─┐
│ 1 │ 2021-03-01 │
│ 1 │ 2021-03-01 │
│ 1 │ 2021-03-02 │
│ 2 │ 2021-03-02 │
│ 2 │ 2021-03-03 │
└─────────┴─────────────┘
If I run SELECT COUNT(*) as count, toDate(login_time) as l FROM some_table GROUP BY l I get following result:
┌─count───┬──login_time─┐
│ 2 │ 2021-03-01 │
│ 2 │ 2021-03-02 │
│ 1 │ 2021-03-03 │
└─────────┴─────────────┘
I would like to reformat the result to show COUNT on a weekly level, instead of every day, as I currently do.
My result for the above example could look something like this:
┌──count──┬──year─┬──month──┬─week ordinal┐
│ 5 │ 2021 │ 03 │ 1 │
│ 0 │ 2021 │ 03 │ 2 │
│ 0 │ 2021 │ 03 │ 3 │
│ 0 │ 2021 │ 03 │ 4 │
└─────────┴───────┴─────────┴─────────────┘
I have gone through the documentation, found some interesting functions, but did not manage to make them solve my problem.
I have never worked with clickhouse before and am not very experienced with SQL, which is why I ask here for help.

Answer 1

Try this query:
select count() count, toYear(start_of_month) year, toMonth(start_of_month) month,
toWeek(start_of_week) - toWeek(start_of_month) + 1 AS "week ordinal"
from (
select *, toStartOfMonth(login_time) start_of_month,
toStartOfWeek(login_time) start_of_week
from (
/* emulate test dataset */
select data.1 user_id, toDate(data.2) login_time
from (
select arrayJoin([
(1, '2021-02-27'),
(1, '2021-02-28'),
(1, '2021-03-01'),
(1, '2021-03-01'),
(1, '2021-03-02'),
(2, '2021-03-02'),
(2, '2021-03-03'),
(2, '2021-03-08'),
(2, '2021-03-16'),
(2, '2021-04-01')]) data)
)
)
group by start_of_month, start_of_week
order by start_of_month, start_of_week
/*
┌─count─┬─year─┬─month─┬─week ordinal─┐
│ 1 │ 2021 │ 2 │ 4 │
│ 1 │ 2021 │ 2 │ 5 │
│ 5 │ 2021 │ 3 │ 1 │
│ 1 │ 2021 │ 3 │ 2 │
│ 1 │ 2021 │ 3 │ 3 │
│ 1 │ 2021 │ 4 │ 1 │
└───────┴──────┴───────┴──────────────┘
*/