Can anyone recommend any exemplar flink projects which show testing, layout, and other useful, practical applications? Java and SQL would probably be the languages.

Which language (JVM or Python) and which APIs (DataStream, Table, SQL)?

JVM. Would like a SQL implementation, but probably would have to put in Java using DataStream

One example could be https://github.com/immerok/recipes/tree/main/table-deduplicated-join which is explained at https://docs.immerok.cloud/docs/how-to-guides/development/joining-and-deduplicating-data/. That's an example that using both DataStream and Table API, including SQL