Re: Desirability of client-side expressions in psql? - Mailing list pgsql-hackers

Hello Pavel,

This is a discussion without actual patch intended for pg12, to be added
to CF 2018-09. The expected end result is either "returned with feedback",
meaning proceed to send some big patch(es), or "rejected", meaning the
project does not want this, no point in submitting something.

please, can you port expression evaluation from pgbench to psql? I miss a
patch.

Indeed, I have not done it yet:-)

This is a pretty large series of patches, which would take a significant time for developing (me), rewiewing (not me) and committing (with overload committers). I would not like to end in the "we do not want this feature at all" state *after* the time has been spent, hence this pre-patch call for discussion about the feature itself, before diving into coding.

I take note that you are interested in actually having this feature.

I am sure so psql expression evaluation has strong benefit - mainly for
expressions like

\if SERVER_VERSION_NUM >= xxxx
 ...
\endif

Note that this can already be done by relying on server-side expressions:

 SELECT :SERVER_VERSION_NUM >= 110000 AS "version_11_plus" \gset
 \if :version_11_plus
   ...
 \endif

Not very elegant, but functional. I'm not sure there is a compelling reason to have this feature beyond elegance.

--
Fabien.