Running marketing Referencing columns by numbers

65. Referencing columns by numbers

Let’s look at our latest query with GROUP BY:

SELECT signup_date, country, COUNT(*) AS users_count FROM users GROUP BY country, signup_date ORDER BY signup_date DESC, country ASC

As you can see we’ve duplicated country and signup_date columns 3 times ⚠. It definitely could be improved.

In programming there’s a DRY principle – Dont Repeat Yourself. It has many variations, but the idea is that the first time you need to duplicate something is OK. The second time you’re duplicating this thing it’s time to refactor the code and remove duplication.

We...

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