WITH
first AS
      (SELECT u.user_id,
             CAST(DATE_TRUNC('month', e.event_time) as date) AS first_date
      FROM tools_shop.users u
      JOIN tools_shop.orders o ON u.user_id = o.user_id
      JOIN tools_shop.events e ON u.user_id = e.user_id
      GROUP BY u.user_id, first_date),
     
cohort_users AS
  (SELECT first_date,
          COUNT(DISTINCT user_id) AS num_users
   FROM first
   GROUP BY first_date)
   
SELECT 
       first_date,
       num_users
FROM cohort_users