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

On 5 September 2017 at 09:58, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> Robert Haas <robertmhaas(at)gmail(dot)com> writes:
>> On Tue, Sep 5, 2017 at 12:16 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>>> Hm. I think it would be a fine idea to push this change into v10,
>>> so that all psql versions that have \if would have these variables.
>>> However, I'm less enthused about adding them to the 9.x branches.
>>> Given the lack of \if, I'm not seeing a use-case that would justify
>>> taking any compatibility risk for.
>>>
>>> Opinions anyone?
>
>> As I see it, the risks of back-patching are:
>
>> 1. Different minor versions will have different behavior, and that
>> tends to create more problems than it solves.
>
> Yeah. Whatever use-case you think might exist for these variables in,
> say, 9.6 is greatly weakened by the fact that releases through 9.6.5
> don't have them.

Makes sense

> However, since v10 is still in beta I don't think that argument
> applies to it.

OK

Does raise the further question of how psql behaves when we connect to
a pre-10 server, so we have SERVER_VERSION_NUM but yet it is not set.
How does this
\if SERVER_VERSION_NUM < x
behave if unset? Presumably it fails, even though the version *is* less than x
Do we need some macro or suggested special handling?

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