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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.
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a subquery only if you're not interested in speed
No need to even use the inner join just run a subquery in the where cluase.
A left Join is more efficeint then a subquery but not more the an inner join.
It probly depends on the Database Management system. Can't say it for postgres. AFAIK, SQL server and DB2 don't care. I would use the on clause for joining the tables only and the where for limiting the result set.
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