This community-built FAQ covers the “Review” exercise from the lesson “Multiple Tables”.
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Data Science
Learn SQL
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I’ve build up some tables and I’m happy with my result and I want to share it! I’m just a beginner of programming and thx for the courses I really learnt a lot!!
-- Table 1
WITH report_1 AS(
WITH report AS(
SELECT customer_id, subscription_id, COUNT(subscription_id) AS 'quantity'
FROM orders
GROUP BY 1,2)
SELECT report.customer_id, subscriptions.description, report.quantity
FROM subscriptions
JOIN report
ON subscriptions.subscription_id = report.subscription_id)
SELECT customers.customer_id AS 'ID', customers.customer_name AS 'Customer Name', report_1.description AS 'Magazine', report_1.quantity AS 'Quantity'
FROM customers
JOIN report_1
ON report_1.customer_id = customers.customer_id
ORDER BY 1;
-- Table 2 (Short Form)
WITH report_1 AS(
WITH report AS(
SELECT customer_id, subscription_id, COUNT(subscription_id) AS 'quantity'
FROM orders
GROUP BY 1,2)
SELECT report.customer_id, subscriptions.description, report.quantity
FROM subscriptions
JOIN report
ON subscriptions.subscription_id = report.subscription_id)
SELECT customers.customer_id AS 'ID',
CASE
WHEN report_1.description LIKE '%Politics%' THEN 'P'
WHEN report_1.description LIKE '%Sports%' THEN 'S'
WHEN report_1.description LIKE '%Fashion%' THEN 'F'
ELSE NULL
END AS 'Magazine',
report_1.quantity AS 'Quantity'
FROM customers
JOIN report_1
ON report_1.customer_id = customers.customer_id
ORDER BY 1;
-- Table 3 (for purchasing easy reference)
SELECT Magazine, COUNT(*)
FROM(
WITH report_1 AS(
WITH report AS(
SELECT customer_id, subscription_id, COUNT(subscription_id) AS 'quantity'
FROM orders
GROUP BY 1,2)
SELECT report.customer_id, subscriptions.description, report.quantity
FROM subscriptions
JOIN report
ON subscriptions.subscription_id = report.subscription_id)
SELECT customers.customer_id AS 'ID',
CASE
WHEN report_1.description LIKE '%Politics%' THEN 'P'
WHEN report_1.description LIKE '%Sports%' THEN 'S'
WHEN report_1.description LIKE '%Fashion%' THEN 'F'
ELSE NULL
END AS 'Magazine',
report_1.quantity AS 'Quantity'
FROM customers
JOIN report_1
ON report_1.customer_id = customers.customer_id
ORDER BY 1)
GROUP BY Magazine
ORDER BY 2;
I tried all three of your queries but not one of them worked!?
I didn’t get any errors but I didn’t get any results either… very strange! Could you post a screen grab of your results?
Thanks for posting and tweaking my interest!
Dennis
Reward your top 5 buyers!
WITH previous_query AS (
SELECT customer_id,
COUNT(subscription_id) AS 'subscriptions'
FROM orders
GROUP BY customer_id
)
SELECT customers.customer_name,
previous_query.subscriptions
FROM previous_query
JOIN customers
ON previous_query.customer_id = customers.customer_id
--sort the results!
ORDER BY previous_query.subscriptions DESC
LIMIT 5;
Hi Dennis! Thx for your reply :]
I think it was the copy and paste issue since I was working this on evernote therefore some formatted text is pasted here. I’ve edited my post and I think the code can work now.
And nice idea for your table too! 
hi guys,
Can “ORDER BY and LIMIT” commands be used when using “JOIN”?
Hi, I tried to create a view that would tell how many magazines where purchased by month, since all appear to have been purchased on january, I changed it to classify them as first half of jan (1 to 15) and second half (16 to 31). Just the first magazine works with this classification, but the rest just set them to second half, anyone see my error?
/* for each subscription how many purchases had in the first half of the month vs the second*/
select subscriptions.subscription_id, subscriptions.description, orders.order_id, orders.purchase_date,
/* this sums the total amount of sold magazines per subscription id*/
sum(case
when orders.purchase_date is null then 0
else 1
end) as 'total_sold',
/*this groups them by first half and second hafl of the month january*/
case
when orders.purchase_date is null then null
when orders.purchase_date <= '01-15-2017' then 'First half'
when orders.purchase_date >= '01-16-2017' then 'Second half'
end as 'period'
from subscriptions
left join orders
on subscriptions.subscription_id = orders.subscription_id
group by subscriptions.subscription_id, period
order by subscriptions.subscription_id, period;
/* test if subscription id n really have only x orders*/
select subscriptions.subscription_id, subscriptions.description, count(subscriptions.subscription_id) as 'purchases'
from subscriptions
left join orders
on subscriptions.subscription_id = orders.subscription_id
group by subscriptions.subscription_id;
select *,
case
when orders.purchase_date is null then null
when orders.purchase_date <= '01-15-2017' then 'First half'
when orders.purchase_date >= '01-16-2017' then 'Second half'
end as 'period'
from orders
order by subscription_id;
Is there any cheatsheets for multiple tables? I need it for my notes…
nvm i found it: https://www.codecademy.com/learn/learn-sql/modules/learn-sql-multiple-tables/cheatsheet
but it’s not included in review section of multiple tables like it used to in another chapter
