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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.
When refactoring, anything can change. I don't see this as a good reason to avoid numbers in a group by.
Using numbers in GROUP BY clause is a real bad practice. The order of columns can change which can break the code.