Re: COPY FROM WHEN condition

On Fri, Nov 02, 2018 at 12:58:12PM +0100, Daniel Verite wrote:
>     Pavel Stehule wrote:
> 
> > > SELECT x.a, sum(x.b)
> > > FROM ( COPY INLINE '/path/to/foo.txt' FORMAT CSV ) as x( a integer, b
> > > numeric, c text, d date, e json) )
> > > WHERE x.d >= '2018-11-01'
> > >
> > >
> > Without some special feature this example is not extra useful. It is based
> > on copy on server that can use only super user with full rights.
> 
> And if superuser, one might use the file data wrapper [1]  to get
> the same results without the need for the explicit COPY in the query.
> 
> BTW, this brings into question whether the [WHEN condition] clause
> should be included in the options of file_fdw, as it supports pretty
> much all COPY options.
> 
> Also, psql's \copy should gain the option too?

tl;dr: \copy support is a very large can of worms.

psql's \copy is something which should probably be handled separately
from COPY, as it's both a way to access the filesystem without
superuser permission and an interface to the COPY part of the
protocol.  It seems like poor design to add grammar to support a
single client, so we'd need to think about this in terms of what we
want to support on the client side independent of specific clients. It
also seems like a violation of separation of concerns to couple FEBE
to grammar, so there'd need to be some way to do those things
separately, too.

Best,
David.
-- 
David Fetter <david(at)fetter(dot)org> http://fetter.org/
Phone: +1 415 235 3778

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