SQL Habit

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 the following code from Lesson 109.. how come we dont need to group by utm_campaign at the end when we are calculating CPA? is it because we joined the users to the row by utm_campaign?

WITH spend_per_campaign AS (
  SELECT
    utm_campaign,
    SUM(amount) AS total_spend
  FROM marketing_spends
  GROUP BY 1  
), users_per_campaign AS (
  SELECT
    utm_campaign,
    COUNT(*) AS users_count
  FROM users
  WHERE 
    utm_campaign IS NOT NULL
  GROUP BY 1
)

SELECT
  s.utm_campaign,
  users_count,
  total_spend / users_count AS CPA
FROM spend_per_campaign s
INNER JOIN users_per_campaign u
  ON s.utm_campaign= u.utm_campaign

Does this look correct for the homework at the bottom of lesson 108 where it asks to add country to the CTE?

I chose inner join instead of left join but i dont think it would matter if i did left join?

WITH customers AS (
  SELECT
    a.user_id,
    b.country,
    MIN(a.created_at) AS first_purchased_at
  FROM purchases a
  inner join users b
  on a.user_id = b.id
  WHERE
    refunded = FALSE
  GROUP BY 1,2
  ORDER BY 3 DESC
)		

SELECT *
FROM customers

Can someone explain why we use the first code where the refunded = false is in the join statement and not in the where condition?

It seems like the lesson is saying that we use it in the join and not where because if we use it in the where we exclude the free users since they never made a purchase but isnt this what we want? I thought ARPU was total revenue / total paying customers..

If I use the code where the refunded = false is in the join statement and count distinct id from the users table then im counting every user who has a utm_campaign.

Also, why do we say utm_campaign has to be null.. shouldnt ARPU just look at total revenue/paying customers regardless of whether or not they came from our marketing?