SQL - Unequal left join BigQuery

Question

New here. I am trying to get the Daily and Weekly active users over time. they have 30 days before they are considered inactive. My goal is to create graph\'s that can be sp

Answer 1

Below is for BigQuery Standard SQL and mostly reproduce logic in your query with exception of not including days where no activity at all is found

#standardSQL
SELECT
    daily_use.user_id
  , wd.date AS DATE
  , MIN(DATE_DIFF(wd.date, daily_use.activity_date, DAY)) AS days_since_last_action
FROM dates AS wd
CROSS JOIN daily_use
WHERE wd.date BETWEEN 
  daily_use.activity_date AND DATE_ADD(daily_use.activity_date, INTERVAL 30 DAY)
GROUP BY 1,2
-- ORDER BY 1,2

if for whatever reason you still need to exactly reproduce your logic - you can embrace above with final left join as below:

#standardSQL
SELECT *
FROM dates AS wd
LEFT JOIN (
  SELECT
    daily_use.user_id
    , wd.date AS date
    , MIN(DATE_DIFF(wd.date, daily_use.activity_date, DAY)) AS days_since_last_action
  FROM dates AS wd
  CROSS JOIN daily_use
  WHERE wd.date BETWEEN 
    daily_use.activity_date AND DATE_ADD(daily_use.activity_date, INTERVAL 30 DAY)
  GROUP BY 1,2
) AS daily_use
USING (date)
-- ORDER BY 1,2