Re: proposal: psql PSQL_TABULAR_PAGER variable

po 22. 4. 2019 v 16:21 odesílatel Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> napsal:

> Robert Haas <robertmhaas(at)gmail(dot)com> writes:
> > Seems like pspg could just hand off to the regular pager if it
> > discovers that the input is not in a format it finds suitable.
>
> It might be slightly tricky to do that after having already consumed
> some of the input :-(.
>

pspg supports both direction scrolling, so data are in buffer, and can be
displayed again.

> Still, I've got to say that I find this proposal pretty horrid.
> I already thought that PSQL_PAGER was a dubious idea: what other
> program do you know anywhere that isn't satisfied with PAGER?
> Inventing still more variables of the same ilk is making it even
> messier, and more obviously poorly designed, and more obviously
> likely to end up with forty-nine different variables for slightly
> different purposes.
>

The programs with some complex output usually doesn't use a pagers - or use
pagers only for part of their output.

Initially I would to teach "less" to support tabular data - but the after
some initial research I found so I am not able to modify "less".

> I think that the general problem here is "we need psql to be able to
> give some context info to pspg", and the obvious way to handle that
> is to make a provision for arguments on pspg's command line. That
> is, instead of just calling "pspg", call "pspg table" or "pspg help"
> etc etc, with the understanding that the set of context words could
> be extended over time. We could shoehorn this into what we already
> have by saying that PSQL_PAGER is interpreted as a format, and if
> it contains say "%c" then replace that with a context word (and
> again, there's room for more format codes over time). Probably
> best *not* to apply such an interpretation to PAGER, though.
>

It can be a way. There are some issues unfixable on pager side - like
dynamic column resizing when FETCH_COUNT > 0 and some others.

I can imagine a situation, when psql send just raw data in some easy
machine readable format (like CSV), and specialized pager can format these
data, and can support some interactive work (hiding columns, columns
switch, ..)

Regards

Pavel

>
> Whether the whole problem is really worth this much infrastructure
> is a fair question. But if we're going to do something, I'd rather
> go down a path like this than inventing a new environment variable
> every month.
>
> regards, tom lane
>