I'd like to propose adding a LIMIT option to COPY FROM, which limits the number of rows to load.
With COPY TO, we can use the LIMIT clause in the query to restrict output rows, but COPY FROM has no equivalent way to limit the number of rows to load (except using the PROGRAM option with external tools like head). This patch resolves that asymmetry.
Syntax example: - COPY t FROM STDIN (LIMIT 100);
I work with such scenarios a lot and I can't see why COPY should worry itself about such filtering.
IRL most of what goes into COPY'S STDIN has already been filtered extensively,
