It would be convenient to reference aliased tables that are not on top of the RelBuilder stack.
I don't see anything preventing conflicting alias names. should this be validated in the Frame constructor?
Yes, I think that would be useful. But if we allow null alias names (I don't remember) we should continue to allow that.
Fixed in http://git-wip-us.apache.org/repos/asf/calcite/commit/ffe1a68d. Thanks for the PR, Jess Balint!
Resolved in release 1.11.0 (2017-01-11).