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...

“well worth the money”
Sign up and check out 36 free lessons and exercises.

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. 🚀

“well worth the money”

Fluent in SQL in a month

Master Data Analysis with SQL with real life examples from Product Management, Marketing, Finance and more.
-- Type your query here, for example this one -- lists all records from users table: SELECT * FROM users
LIMIT 500
Loading chart... ⏳