WITH user_activity AS (
  SELECT DISTINCT
    DATE_TRUNC('month', order_date) :: DATE AS delivr_month,
    user_id
  FROM orders)


SELECT
  previous.delivr_month,
  ROUND(
    COUNT(DISTINCT current.user_id) :: NUMERIC /
    GREATEST(COUNT(DISTINCT previous.user_id), 1),
  2) AS retention

FROM user_activity AS previous
LEFT JOIN user_activity AS current
ON previous.user_id = current.user_id
AND previous.delivr_month = (current.delivr_month - INTERVAL '1 month')
GROUP BY previous.delivr_month
ORDER BY previous.delivr_month ASC
LIMIT 3;