I really like how Flink is incorporating SQL as a first class citizen.

If you're interested in stuff like this, keep an eye on OctoSQL[1].

We're working hard on event time streaming with exactly-once semantics in pure SQL, being greatly inspired by the work and research done by the Flink contributors.

It's our Bachelor Thesis actually. Though we have much left to work on, with features like distributed execution, so there's still a long way ahead!

[1]: https://github.com/cube2222/octosql