Calculate the streaks of visit of users limited to 7 - sql

Question

I am trying to calculate the consecutive visits a user makes on an app. I used the rank function to determine the streaks maintained by each user. However, my requirement is that the streaks should not exceed 7.
For instance, if a user visits the app for 9 consecutive days. He will have 2 different streaks: one with count 7 and the other with 2.
Using MaxCompute. It's similar to MySQL.
I have the following table named visitors_data:
user_id visit_date
murtaza 01-01-2021
john 01-01-2021
murtaza 02-01-2021
murtaza 03-01-2021
murtaza 04-01-2021
john 01-01-2021
murtaza 05-01-2021
murtaza 06-01-2021
john 02-01-2021
john 03-01-2021
murtaza 07-01-2021
murtaza 08-01-2021
murtaza 09-01-2021
john 20-01-2021
john 21-01-2021
Output should look like this:
user_id streak
murtaza 7
murtaza 2
john 3
john 2
I was able to get the streaks by the following query, but I could not limit the streaks to 7.
WITH groups AS (
SELECT user_id,
RANK() OVER (ORDER BY user_id, visit_date) AS RANK,
visit_date,
DATEADD(visit_date, -RANK() OVER (ORDER BY user_id, visit_date), 'dd') AS date_group
FROM visitors_data
ORDER BY user_id, visit_date)
SELECT
user_id,
COUNT(*) AS streak
FROM groups
GROUP BY
user_id,
date_group
HAVING COUNT(*)>1
ORDER BY COUNT(*);

Answer 1

My thinking ran along similar lines to forpas':
SELECT user_id, COUNT(*) streak
FROM
(
SELECT
user_id, streak,
FLOOR((ROW_NUMBER() OVER (PARTITION BY user_id, streak ORDER BY visit_date)-1)/7) substreak
FROM
(
SELECT
user_id, visit_date,
SUM(runtot) OVER (PARTITION BY user_id ORDER BY visit_date) streak
FROM (
SELECT
user_id, visit_date,
CASE WHEN DATE_ADD(visit_date, INTERVAL -1 DAY) = LAG(visit_date) OVER (PARTITION BY user_id ORDER BY visit_date) THEN 0 ELSE 1 END as runtot
FROM visitors_data
GROUP BY user_id, visit_date
) x
) y
) z
GROUP BY user_id, streak, substreak
As an explanation of how this works; a usual trick for counting runs of successive records is to use LAG to examine the record before and if there is only e.g. one day difference then put a 0, otherwise put a 1. This then means the first record of a consecutive run is 1, and the rest are 0, so the column ends up looking like ​1,0,0,0,1,0... SUM OVER ORDER BY sums this in a "running total" fashion. This effectively means it forms a counter that ticks up every time the start of a run is encountered so a run of 4 days followed by a gap then a run of 3 days looks like 1,1,1,1,2,2,2 etc and it forms a "streak ID number".
If this is then fed into a row numbering that partitions by the streak ID number, it establishes an incrementing counter that restarts every time the streak ID changes. If we sub 1 off this so it runs from 0 instead of 1 then we can divide it by 7 to get a "sub streak ID" for our 9-long streak that is 0,0,0,0,0,0,0,1,1 (and so on. A streak of 25 would have 7 zeroes, 7 ones, 7 twos, and 4 threes)
All that remains then is to group by the user, the streak ID, the substreakID and count the result
Before the final group and count the data looks like:
Which should give some idea of how it all works

Answer 2

With a mix of window functions and aggregation:
SELECT user_id, COALESCE(NULLIF(MAX(counter) % 7, 0), 7) streak
FROM (
SELECT *, COUNT(*) OVER (PARTITION BY user_id, grp ORDER BY visit_date) counter
FROM (
SELECT *, SUM(flag) OVER (PARTITION BY user_id ORDER BY visit_date) grp
FROM (
SELECT *, COALESCE(DATE_ADD(visit_date, INTERVAL -1 DAY) <>
LAG(visit_date) OVER (PARTITION BY user_id ORDER BY visit_date), 1) flag
FROM (SELECT DISTINCT * FROM visitors_data) t
) t
) t
) t
GROUP BY user_id, grp, FLOOR((counter - 1) / 7)
See the demo.

Answer 3

You could break them up after the fact. For instance, if you never have more than 21:
SELECT user_id, LEAST(streak, 7)
FROM (SELECT user_id, COUNT(*) AS streak
FROM groups
GROUP BY user_id, date_group
HAVING COUNT(*) > 1
) gu JOIN
(SELECT 1 as n UNION ALL SELECT 2 as n UNION ALL SELECT 3 UNION ALL SELECT 4
) n
ON streak >= n * 7
ORDER BY LEAST(streak, 7);
If you have an indeterminate number range for the longest streak, you can do something similar with a recursive CTE>