In this lesson I’d like to point out another nuance when calculating unit economics metrics per cohort (campaign, channel etc). We already saw that the wrong type of join could remove some cohorts from the result completely (if campaign has no signups yet it’ll be filter out with INNER JOIN
).
This is why we always should use LEFT JOIN
in such calculations. To ensure that our report contains data on all campaigns we’re running, even those with 0 signups or customers. Let’s consider the query for calculating CAC per campaign:
WITH spends AS (...
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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
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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. 