SQLite group datetime by 168 hours (7 days) gives NULL back - sql

Question

I have an Orders table in my SQLite database. What I want to do is group by the data by every 168 hours (7 days), and count to total Orders per 168 hours.
What I did was create an in memory "calendar table" and I joined my Orders table to that calendar set.
This works fine when I group by 12, 24, 48 or even 120 hours (5 days). But for some reason it doesn't work when I group by 168 hours (7 days). I get NULL values back instead of what count() should really return.
The following sql code is an example that groups by every 120 hours (5 days).
CREATE TABLE IF NOT EXISTS Orders (
Id INTEGER NOT NULL PRIMARY KEY AUTOINCREMENT,
Key TEXT,
Timestamp TEXT NOT NULL
);
INSERT INTO Orders (Key, Timestamp) VALUES ('k1', '2019-10-01 10:00:23');
INSERT INTO Orders (Key, Timestamp) VALUES ('k2', '2019-10-01 15:45:19');
INSERT INTO Orders (Key, Timestamp) VALUES ('k3', '2019-10-02 17:05:19');
INSERT INTO Orders (Key, Timestamp) VALUES ('k4', '2019-10-03 20:12:19');
INSERT INTO Orders (Key, Timestamp) VALUES ('k5', '2019-10-04 08:49:19');
INSERT INTO Orders (Key, Timestamp) VALUES ('k6', '2019-10-05 11:24:19');
INSERT INTO Orders (Key, Timestamp) VALUES ('k7', '2019-10-07 11:24:19');
WITH RECURSIVE dates(date1) AS (
VALUES('2019-10-01 00:00:00')
UNION ALL
SELECT datetime(date1, '+120 hours')
FROM dates
WHERE date1 <= '2019-10-29 00:00:00'
)
SELECT date1 as __ddd, d2.* FROM dates AS d1
LEFT JOIN (
SELECT count(Key) AS OrderKey,
datetime((strftime('%s', timestamp) / 432000) * 432000, 'unixepoch') as __interval
FROM `Orders`
WHERE `Timestamp` >= '2019-09-29T00:00:00.000'
GROUP BY __interval LIMIT 10
) d2 ON d1.date1 = d2.__interval
Important note:
If you want to update this code to test it with 168 hours (7 days), then you should do the following:
Change +120 hours to +168 hours
Change 432000 (432000 == 120 hours) to 604800 (604800 == 168 hours)
note that this number occurs twice, both should be replaced
Anyone any idea why it stops working properly when I change the sql code to 168 hours?

Answer 1

Your problem is that when you change to a 7-day interval, the values in your dates CTE don't align with the intervals generated from your Orders table. You can fix that by making the dates CTE start on a similarly aligned date:
WITH RECURSIVE dates(date1) AS (
SELECT datetime((strftime('%s', '2019-10-01 00:00:00') / 604800) * 604800, 'unixepoch')
UNION ALL
SELECT datetime(date1, '+168 hours')
FROM dates
WHERE date1 <= '2019-10-29 00:00:00'
)
Output:
__ddd OrderKey __interval
2019-09-26 00:00:00 3 2019-09-26 00:00:00
2019-10-03 00:00:00 4 2019-10-03 00:00:00
2019-10-10 00:00:00 null null
2019-10-17 00:00:00 null null
2019-10-24 00:00:00 null null
2019-10-31 00:00:00 null null
Demo on dbfiddle