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Collections are a way for you to organize kata so that you can create your own training routines. Every collection you create is public and automatically sharable with other warriors. After you have added a few kata to a collection you and others can train on the kata contained within the collection.
Get started now by creating a new collection.
In real scenarios you likely want a distinct in the count:
select age, count(distinct id) as people_count
from people
group by age
For some reason that doesn't work and does not return the right results in this kata.
Why do you need to order by species? It wouldn't accept my solution until I did but the problem description does not seem to indicate that it requires a specific order.