Could be splited further

Nice job on the query:

WITH first_touch AS (
    SELECT user_id,
        MIN(timestamp) as first_touch_at
    FROM page_visits
    GROUP BY user_id)
SELECT count(ft.user_id),
    --ft.first_touch_at,
    pv.utm_source,
    pv.utm_campaign
FROM first_touch ft
JOIN page_visits pv
    ON ft.user_id = pv.user_id
    AND ft.first_touch_at = pv.timestamp  
    group by utm_campaign;

I would even, split the the second query into 2 and do the aggregation on the third. It looks little cleaner. Also, I would add an order by.

WITH first_touch AS (
  SELECT user_id,
         MIN(timestamp) AS first_touch_at
  FROM page_visits
  GROUP BY 1),
ft_attr AS (
  SELECT ft.user_id,
         ft.first_touch_at,
         pv.utm_campaign
  FROM first_touch ft
  JOIN page_visits pv
    ON ft.user_id = pv.user_id
    AND ft.first_touch_at = pv.timestamp
)
SELECT ft_attr.utm_campaign,
       COUNT(*)
FROM ft_attr
GROUP BY 1
ORDER BY 2 DESC;

Jssy2018 / sql-scratch-capstone-turn-in

Could be splited further #1