# 105. Calculating ARPU

To calculate ARPU we need to divide revenues from a cohort of users (all users or users from a certain marketing campaign, for example) by the number of these users. It’s a very simple query with a `LEFT JOIN` but there are a couple of very important nuances we need to get. I need all your attention right now Ready? Let’s go

Here’s a query that calculates ARPU:

``SELECT SUM(amount) / COUNT(DISTINCT(u.id)) AS ARPU FROM users u LEFT JOIN purchases p ON u.id = p.user_id AND refunded = FALSE ``

## First nuance: count unique users

We used `DISTINCT` to count...

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Hi, it’s Anatoli, the author of SQL Habit.

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-- Type your query here, for example this one -- lists all records from users table: SELECT * FROM users