https://www.mongodb.com/es/docs/upcoming/reference/operator/projection/positional/
$ (projection operator) - Database Manual - MongoDB Docs
Limit array contents using the positional `$` operator to return the first element matching a query condition in MongoDB.
projection operatordatabasemanualmongodbdocs
https://www.mongodb.com/es/docs/upcoming/reference/operator/projection/elemmatch/
$elemMatch (projection operator) - Database Manual - MongoDB Docs
Limit array field results using `$elemMatch` to return only the first element matching specified conditions in MongoDB queries.
projection operatordatabasemanualmongodbdocs
https://mail-archive.com/search?l=github@datafusion.apache.org&q=subject:%22Re%5C%3A+%5C%5BPR%5C%5D+Support+for+projection+item+prefix+operator+%5C%28CONNECT_BY_ROOT%5C%29+%5C%5Bdatafusion%5C-sqlparser%5C-rs%5C%5D%22&o=newest&f=1
subject:"Re\: \[PR\] Support for projection item prefix operator \(CONNECT_BY_ROOT\)...
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