Comment by maximilianroos

Yes this is a good idea. dplyr has something similar with `mutate` & `transmute`.

This could _mostly_ be enforced by PRQL. There's a case where we transpile to:

  select *, x+1 as x_plus_one

...where we don't know whether or not we're overwriting an existing column. But it's a minority of cases, and the contract could stand within PRQL.

I opened an issue here: https://github.com/max-sixty/prql/issues/6