Re: [HACKERS] [COMMITTERS] pgsql: Add psql variables showing serverversion and psql version.

>> Thus short, simple but meaningful examples which show how to do something
>> useful with all that in the documentation may help people take advantage
>> of these new features.
>
> I don't have an objection to providing an example.  I wasn't terribly
> impressed with Simon's version, but maybe we can do better.

That was just a quick idea to show how they could be used, probably it can 
be improved.

> I think it should be concrete, not partly abstract; and likely it needs 
> to be with \if not the variable proper.

ISTM that currently there is no "not". Maybe I do not understand your 
sentence.

>> Given my experience with "\d*", I'm not sure I would assume that a new
>> psql feature would work with older servers.
>
> I don't recall anyone questioning whether PQserverVersion() would work
> with older servers.  Being able to tell what version the server is is
> sort of the point, no?  If there were a restriction on what it would
> work with, I would agree that that needs to be documented.  But I
> don't think "yes, it really works" is a helpful use of documentation
> space.

Sure.

I can use psql without knowing that there is a libpq underneath, that it 
contains a PQserverVersion function implemented since pg7, and that the 
SERVER_VERSION_* variables introduced in pg10 or pg11 rely on that thus it 
should work with pg7/8/9 as well. It is not obvious, as a new feature 
could depend on any combination of server side functions, protocol 
extension, client library functions or client code...

-- 
Fabien.