Fixed range of timestamps for every uuid in SQL - postgresql

Question

I would like to generate a table with the last n weeks timestamps of data (in this case, n=3) and all the data, even if it is null.
I am using the following pieces of code
with raw_weekly_data as (SELECT
distinct d.uuid,
date_trunc('week',a.start_timestamp) as tstamp,
avg(price) as price
FROM
a join d on a.uuid = d.uuid
where start_timestamp between date_trunc('week',now()) - interval '3 week' and date_trunc('week',now())
group by 1,2,3
order by 1)
,tstamp as (SELECT
distinct tstamp
FROM
raw_weekly_data
)
SELECT
t.tstamp,
r.*
from raw_weekly_data r right join tstamp t on r.tstamp = t.tstamp
order by uuid
I would like to have something like that:
week | uuid | price
w1 | 1 | 10
w2 | 1 | 2
w3 | 1 |
w1 | 2 | 20
w2 | 2 |
w3 | 2 |
w1 | 3 | 10
w2 | 3 | 10
w3 | 3 | 20
But instead all the null results are not showed. What is the best approach in here?
week | uuid | price
w1 | 1 | 10
w2 | 1 | 2
w1 | 2 | 20
w1 | 3 | 10
w2 | 3 | 10
w3 | 3 | 20

Answer 1

Form a Cartesian product of all weeks an UUIDs, then LEFT JOIN to actual avg, prices per (week, uuid). Like:
SELECT *
FROM generate_series (date_trunc('week', now() - interval '3 week')
, now() - interval '1 week'
, interval '1 week') tstamp
CROSS JOIN (SELECT DISTINCT uuid FROM a) a
LEFT JOIN (
SELECT d.uuid
, date_trunc('week', a.start_timestamp) AS tstamp
, avg(price) AS price -- d.price?
FROM a
JOIN d USING (uuid)
WHERE a.start_timestamp >= date_trunc('week',now()) - interval '3 week'
AND a.start_timestamp < date_trunc('week',now())
) ad USING (uuid, tstamp)
GROUP BY 1, 2
ORDER BY 1, 2
This way you get all combinations of the last three weeks and UUIDs, extended by the average price - if one should exist for the combination.
Based on some educated guesses to fill in missing information ..