Hi Anatoli!

I have a question about the funnel analysis query in lesson 129, namely this one:

SELECT
  COUNT(h.visitor_id) AS homepage_pvs,
  COUNT(b.visitor_id) AS book_page_pvs
FROM web_analytics.pageviews h
LEFT JOIN web_analytics.pageviews b
  ON h.visitor_id = b.visitor_id
    AND b.url LIKE '%/books/%'
    AND (
      b.referer_url = 'https://www.bindle.com/'
      OR b.referer_url LIKE 'https://www.bindle.com/?%'
    )  
    AND b.created_at BETWEEN h.created_at AND h.created_at + '30 minutes'::interval
WHERE
  h.url = 'https://www.bindle.com/'
  OR h.url LIKE 'https://www.bindle.com/?%'

My question is: Is the

AND (
  b.referer_url = 'https://www.bindle.com/'
  OR b.referer_url LIKE 'https://www.bindle.com/?%'
)

bit necessary, given that we filter using WHERE further down? Is there a difference? They seem to give the same results.

In this code where we setup to capture retention, i know we join the table to itself and specify that the left side table has to be a signup action but we never specify what kind of action the right side (joined table) has to be.. doesnt this mean that technically we could be joining a signup action to itself? If thats the case, shouldnt we specify that the joined table’s action can’t be a signup one?

WITH user_activity AS (
  SELECT
    u.user_id,
    u.created_at::date AS signup_date,
    e.created_at::date AS activity_date,
    COUNT(*) AS events_counts
  FROM mobile_analytics.events u
  LEFT JOIN mobile_analytics.events e
    ON e.user_id = u.user_id  
  WHERE
    u.action = 'signup'  
  GROUP BY 1, 2, 3
  ORDER BY signup_date ASC, user_id ASC
)

SELECT 
  100.0 * COUNT(DISTINCT(CASE WHEN activity_date = '2018-02-08' THEN user_id END)) / COUNT(DISTINCT(user_id)) AS D7_retention_rate
FROM user_activity
WHERE 
  signup_date = '2018-02-01'

Is there a way of doing view-through attribution (when the person saw but not clicked on an ad)?