BigQuery Cross Join Failing - google-bigquery

Question

I'm trying to pull user activity by date. I am trying to built a table of every day since a user account was created, using cross join and a where clause. In my case, cross join cannot be avoided. The calendar table is just a list of all dates for last 365 days (365 rows). The user table has ~1b rows.
Here is the query that fails with insufficient resources:
SELECT
u.user_id as user_id,
date(u.created) as signup_date,
cal.date as date,
from (select date(dt) as date from [dw.calendar] where date(dt) <
CURRENT_DATE() ) cal
cross join each dw.user u
where
date(u.created) <= cal.date
Based on https://cloud.google.com/bigquery/query-reference, cross joins do not even support the "each" clause. How do I perform the above operation to successfully create a table?

Answer 1

You do not need to fill "empty" days to just calculate daily count and perform window function to get the aggregated sum, so you don't even need calendar table for this. To make this happen you need to use RANGE vs. ROWS in your window. See example below (for BigQuery Standard SQL)
#standardSQL
SELECT
user_id, created, daily_count,
SUM(daily_count) OVER(
PARTITION BY user_id ORDER BY created_unix_date DESC
RANGE BETWEEN CURRENT ROW AND 6 FOLLOWING
) weekly_avg
FROM `dw.user`, UNNEST([UNIX_DATE(created)]) AS created_unix_date
ORDER BY user_id, created DESC
i am not sure about exact schema /types of your table so might need to adjust above respectively, but meantime you can test/play with below dummy data
#standardSQL
WITH `dw.user` AS (
SELECT
day AS created,
CAST(1 + 10 * RAND() AS INT64) AS user_id,
CAST(100 * RAND() AS INT64) AS daily_count
FROM UNNEST(GENERATE_DATE_ARRAY('2017-01-01', '2017-04-26')) AS day
)
SELECT
user_id, created, daily_count,
SUM(daily_count) OVER(
PARTITION BY user_id ORDER BY created_unix_date DESC
RANGE BETWEEN CURRENT ROW AND 6 FOLLOWING
) weekly_avg
FROM `dw.user`, UNNEST([UNIX_DATE(created)]) AS created_unix_date
ORDER BY user_id, created DESC