94. JOIN + Aggregate Functions = ❤

If you thought that we’re done with grouping and counting forever – nope, that was only the beginning 😆 The real power of this technique comes when we’re joining different tables and then grouping the records in the joined table.

Let’s look at the example of a query we wrote to check revenues per subscription. It’s time to improve it 🚀

SELECT CASE WHEN product_id = 2 THEN 'monthly' WHEN product_id = 3 THEN 'yearly' ELSE 'other_plan' END AS plan, SUM(amount) AS revenue FROM purchases WHERE refunded = FALSE GROUP BY 1 

The main problem we identified...

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Anatoli Makarevich, author of SQL Habit About SQL Habit

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

SQL Habit is a course (or, as some of the students say, “business simulator”). It’s based on a story of a fictional startup called Bindle. You’ll play a role of their Data Analyst 📊 and solve real-life challenges from Business, Marketing, and Product Management.

SQL Habit course is made of bite-sized lessons (you’re looking at one atm) and exercises. They always have a real-life setting and detailed explanations. You can immediately apply everything you’ve learned at work. 🚀

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