On 06/20/2012 11:02 AM, David Fetter wrote:
Folks,
A co-worker filed a bug against file_fdw where the columns in a
FOREIGN TABLE were scrambled on SELECT. It turned out that this comes
from the (yes, it's documented, but since it's documented in a place
not obviously linked to the bug, it's pretty useless) "feature" of
COPY CSV HEADER whereby the header line is totally ignored in COPY
OUT.
Rather than being totally ignored in the COPY OUT (CSV HEADER) case,
the header line in should be parsed to establish which columns are
where and rearranging the output if needed.
I'm proposing to make the code change here:
http://git.postgresql.org/gitweb/?p=postgresql.git;a=blob;f=src/backend/commands/copy.c;h=98bcb2fcf3370c72b0f0a7c0df76ebe4512e9ab0;hb=refs/heads/master#l2436
and a suitable doc change that talks about reading the header only for
the purpose of matching column names to columns, and throwing away the
output as before.
What say?
First you are talking about COPY IN, not COPY OUT, surely.
This is not a bug, it is documented in exactly the place that all other
COPY options are documented. The file_fdw page refers the reader to the
COPY docs for details. Unless you want us to duplicate the entire COPY
docs in the file_fdw page this seems entirely reasonable.
The current behaviour was discussed at some length back when we
implemented the HEADER feature, IIRC, and is quite intentional. I don't
think we should alter the current behaviour, as plenty of people rely on
it, some to my certain knowledge. I do see a reasonable case for adding
a new behaviour which takes notice of the header line, although it's
likely to have plenty of wrinkles.
Reordering columns like you suggest might well have a significant impact
on COPY performance, BTW. Also note that I created the file_text_array
FDW precisely for people who want to be able to cherry pick and reorder
columns. See <https://github.com/adunstan/file_text_array_fdw>
cheers
andrew
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