QuerydrillPaying customers by country
An SQL exercise from Querydrill. Solve it with a SQL editor in your browser, checked on the rows it returns and again on changed data, and it is checked the moment you submit.
The task
From Marta: "For each country, cleaned as before, how many different people made at least one paid payment? Count a person once even if they have several accounts. Most payers first, then by country." Return country and payers.
What this exercise teaches
COUNT(DISTINCT ...) on a cleaned key counts people, not rows. Without it, repeat payments and duplicate accounts inflate the number.
A hint if you get stuck
Join payments to signups, keep paid payments, then COUNT(DISTINCT LOWER(TRIM(s.email))). Leave out signups with no country.
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