Excellent! In the previous step, we found "good customers" whose average order value is above our criteria. Now, we'd like to create a more generalized report that shows the number of good customers in each weekly registration cohort. Take a look:

WITH good_customers AS (
  SELECT
    c.customer_id,
    registration_date,
    AVG(total_amount) AS avg_order_value
  FROM customers c
  JOIN orders o
    ON c.customer_id = o.customer_id
  GROUP BY c.customer_id, registration_date
  HAVING AVG(total_amount) > 1636
)

SELECT
  DATE_PART('year', registration_date) AS year,
  DATE_PART('week', registration_date) AS week,
  COUNT(*) AS good_customers
FROM good_customers
GROUP BY DATE_PART('year', registration_date), DATE_PART('week', registration_date)
ORDER BY DATE_PART('year', registration_date), DATE_PART('week', registration_date);

As you can see, we put the query from the previous step inside a CTE. In the outer query, in turn, we used the DATE_PART() function to extract the year and week of each customer's registration date. We grouped the good customers into weekly cohorts and counted the number of customers in each cohort.