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