Counting consecutive days in postgres - postgresql

Question

I'm trying to count the number of consecutive days in two tables with the following structure:
| id | email | timestamp |
| -------- | -------------- | -------------- |
| 1 | hello#example.com | 2021-10-22 00:35:22 |
| 2 | hello2#example.com | 2021-10-21 21:17:41 |
| 1 | hello#example.com | 2021-10-19 00:35:22 |
| 1 | hello#example.com | 2021-10-18 00:35:22 |
| 1 | hello#example.com | 2021-10-17 00:35:22 |
I would like to count the number of consecutive days of activity. The data above would show:
| id | email | length |
| -------- | -------------- | -- |
| 1 | hello#example.com | 1 |
| 2 | hello2#example.com | 1 |
| 1 | hello#example.com | 3 |
This is made more difficult because I need to join the two tables using a UNION (or something similar and then run the grouping. I tried to build on this query (Finding the length of a series in postgres) but I'm unable to group by consecutive days.
select max(id) as max_id, email, count(*) as length
from (
select *, row_number() over wa - row_number() over wp as grp
from began_playing_video
window
wp as (partition by email order by id desc),
wa as (order by id desc)
) s
group by email, grp
order by 1 desc
Any ideas on how I could do this in Postgres?

Answer 1

First create an aggregate function in order to count the adjacent dates within an ascendant ordered list. The jsonb data type is used because it allows to mix various data types inside the same array :
CREATE OR REPLACE FUNCTION count_date(x jsonb, y jsonb, d date)
RETURNS jsonb LANGUAGE sql AS
$$
SELECT CASE
WHEN d IS NULL
THEN COALESCE(x,y)
ELSE
to_jsonb(d :: text)
|| CASE
WHEN COALESCE(x,y) = '[]' :: jsonb
THEN '[1]' :: jsonb
WHEN COALESCE(x->>0, y->>0) :: date + 1 = d :: date
THEN jsonb_set(COALESCE(x-0, y-0), '{-1}', to_jsonb(COALESCE(x->>-1, y->>-1) :: integer + 1))
ELSE COALESCE(x-0, y-0) || to_jsonb(1)
END
END ;
$$
DROP AGGREGATE IF EXISTS count_date(jsonb, date) ;
CREATE AGGREGATE count_date(jsonb, date)
(
sfunc = count_date
, stype = jsonb
) ;
Then iterate on the count_date on your table grouped by id :
WITH list AS (
SELECT id, email, count_date('[]', timestamp ORDER BY timestamp :: timestamp) as count_list
FROM your_table
GROUP BY id, email
)
SELECT id, email, jsonb_array_elements(count_list-0) AS length
FROM list