fix: Select expressions no-longer force use of labels

[jimfulton]

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Fixes #78 🦕

[tswast]

Thanks for adding unit tests!

Interesting to use SQLite for unit testing, but I can roll with that.

Long-term we might want to do something with Zeta SQL (name of the BigQuery/Spanner open source implementation), but I think it's a long ways away before we get something usable like a local emulator out of that project.