FAQ: Conditional Aggregates - Combining aggregates II


#1

This community-built FAQ covers the “Combining aggregates II” exercise from the lesson “Conditional Aggregates”.

Paths and Courses
This exercise can be found in the following Codecademy content:

SQL: Table Transformation

FAQs on the exercise Combining aggregates II

There are currently no frequently asked questions associated with this exercise – that’s where you come in! You can contribute to this section by offering your own questions, answers, or clarifications on this exercise. Ask or answer a question by clicking reply (reply) below.

If you’ve had an “aha” moment about the concepts, formatting, syntax, or anything else with this exercise, consider sharing those insights! Teaching others and answering their questions is one of the best ways to learn and stay sharp.

Join the Discussion. Help a fellow learner on their journey.

Ask or answer a question about this exercise by clicking reply (reply) below!

Agree with a comment or answer? Like (like) to up-vote the contribution!

Need broader help or resources? Head here.

Looking for motivation to keep learning? Join our wider discussions.

Learn more about how to use this guide.

Found a bug? Report it!

Have a question about your account or billing? Reach out to our customer support team!

None of the above? Find out where to ask other questions here!


#2

Why does adding a couple of extra brackets here make a difference to how to query runs? Does SQL not follow BODMAS?

SELECT state,
100.0*
(
SUM(CASE WHEN elevation >= 2000
THEN 1 ELSE 0
END)/COUNT(*)
)
AS percentage_high_elevation_airports
FROM airports
GROUP BY state

;


#3

What is the 'Then 1" mean in the case when logic?

SELECT state, 100.0 * sum(CASE WHEN elevation >= 2000 THEN 1 ELSE 0 END) /
count(*) as percentage_high_elevation_airports
FROM airports
GROUP BY state;


#4

What we want to calculate is the ratio of airports with the elevation above 2000 to all the airports in each state. So once there is an airport with the elevation above 2000, we mark it as “1”, and the sum of “1” is the No. of airports with the elevation above 2000. COUNT(*) can help us calculate the No. of all airport in each state, so after dividing these two numbers, we can get the percentage we want.