Q: SQL-style constraints, uniqueness?

[jsshapiro]

Coming from some experience with dependent type systems, CUE looks very interesting and very clever.

A few (hopefully straightforward) questions:

1. Is it possible to specify a value as generated and/or unique?
2. Is it possible to specify something like a foreign key constraint over a single column? Perhaps a form of comprehension?
3. Is it possible to specify constraints across multiple fields/values? Offhand, I'm not clear how to do this neatly without some form of tagged tuple type, but it seems to me that if this existed then the answer for [2] would extend naturally. Perhaps I am not fully understanding definitions, and they might be used for this sort of thing.

Thank you!