Calculating percentages or rates is fundamental to data analysis of any kind. We should feel it by heart, use it as easy as addition or subtraction.
I find the last exercise a perfect material to repeat all the ways we’ve learned so far to calculate percentages.
Percentage with CASE
We know that for every user record there’s at least one record in
devices table. It allows us to calculate percentage of users with a certain
device_type only based on
SELECT 100.0 * COUNT(DISTINCT(CASE WHEN device_type = 'iphone' THEN user_id END)) /...