I found that generated columns and system columns cannot be used in COPY FROM WHERE expressions, but the COPY docs still mentions only the restriction on subqueries.
So I've created the attached patch which updates the docs to also list generated columns and system columns as unsupported in COPY FROM WHERE expressions.
Since generated columns have been rejected in COPY FROM WHERE since v13, that docs change should be backpatched to all supported branches. But the system-column restriction was introduced in v19, so that part does not need to be backpatched.
Thoughts?
Thanks for the patch!
I think it makes sense to add the system columns and generated columns limitation to the documentation, patch LGTM.
