Re: csv format for psql

On Friday, November 9, 2018, Michael Paquier <michael(at)paquier(dot)xyz> wrote:

> On Fri, Nov 09, 2018 at 05:28:07PM +0100, Daniel Verite wrote:
> > But again COPY is concerned with importing the data that preexists,
> > even if it's weird, whereas a psql output formats are not.
>
> Hm. I checked the contents of the patch in details which provide output
> consistent with COPY, but after looking at the global picture I am
> getting cold feet on this patch for a couple of reasons:
> - This stuff adds new code paths in the frontend mimicking what the
> backend already does for years, both doing the same thing.

From the original post:

"copy with csv can't help for the output of meta-commands
such as \gx, \crosstabview, \l, \d ... whereas a CSV format within psql
does work with these."

Formatting is usually a client-side concern so this feature fits well
there. The fact that we’ve provided a server interface for the same doesn’t
preclude its potential desirability in the client.

- There are already three ways to fetch data in this format with COPY,
> \copy and file_fdw, with all three using the same code paths for option
> validations (I can see the arguments at the top of the thread for which
> COPY SELECT can actually do everything you want with?).

Not always conveniently.

> - The experience is confusing, as the psql format uses different options
> than the backend to do the same things:

Yes, those who use psql need to learn its features. I’d posit that since
this syntax is being learned anyway that transferring said knowledge to a
newly added csv format will not be confusing. No more so that having to do
something that is usually client-side (formatting) on the server in the
first place. That we don’t fully replicate the server functionality does’t
bother be. This is meant to be a simple and quick ability that handles 95%
of use cases and defers to the more powerful server version for the
outliers.

Feature-wise I’m on board. Given it’s already written I’d say it should go
in unless there are code complexity and support concerns - which given the
prevalence of other formats I have to believe there are not.

David J.