Hi. I just tried adding the xmin pseudo-column to my COPY,
and I get an error. Using a regular SELECT works fine.
Is that normal? that's a `COPY tab(xmin, cols...) ...`
Do I need to switch to a `COPY (select xmin, cols... from tab) ...` to access xmin?
And if I do that, any performance implications for the COPY?
The reason I'm using COPY is performance and its "streaming" behavior.
(modulo the "big row" non-streaming issue from my as-yet unanswered post from today).
I'm thus interested in how a `COPY tab(cols...)` differs from a `COPY (select cols from tab ...)` in terms of implementation and performance.
Thanks, --DD
