SQL feature wish list

[ryzhyk]

Let's collect additional SQL features we need to implement here.

• [ ] We need a way to distinguish streams from tables. E.g., we currently cannot express a streaming join where one of the inputs gets discarded after each clock tick.
• [ ] We need a way to express time series-related concepts: watermarks, lateness, finalization.
• [ ] Window operators: tumbling, rolling, hopping, session windows (session windows are not yet implemented in DBSP).
• [ ] Recursive queries
• [ ] Store and manipulate complex data types
  • [x] arrays
  • [ ] structs
  • [ ] maps
  • [ ] JSON
  • [x] unnest
• [ ] Support other SQL complex data types
  • [ ] timestamps with timezones
  • [ ] dates with timezones
  • [ ] time
  • [ ] time with timezone
  • [ ] blobs
  • [ ] more operations on decimal
  • [ ] geospatial data types

[mihaibudiu]

Partial duplicate of #41

[mihaibudiu]

UNNEST implemented in #142