TIL - 250122

URL : https://datalemur.com/questions/user-retention

SELECT
  EXTRACT(MONTH FROM event_date)
  ,COUNT(DISTINCT user_id)
FROM user_actions
WHERE 
  EXTRACT(MONTH FROM event_date) = 7
  AND user_id IN (
    SELECT user_id
    FROM user_actions
    WHERE EXTRACT(MONTH FROM event_date) = 6
  )
GROUP BY 1