Re: unexpected psql "feature"

David G. Johnston wrote:
> On Wed, Jul 13, 2016 at 5:44 PM, Fabien COELHO <coelho(at)cri(dot)ensmp(dot)fr> wrote:
>
> > Although "\;" behavior is not documented, I would have expected both
> >>> results to be shown one after the other, or having a an error, but not a
> >>> quiet discard.
> >>
> >> See the documentation for PQexec(): all but the last query result is
> >> discarded.
> >
> > Sure. That is developer-level answer to "why", although it does not really
> > say why the developer chose PQexex over PQsendQuery. At the user-level the
> > behavior is still pretty surprising.
>
> ​Lets try putting it this way...
>
> As a psql user I want some way to choose whether I send my query via
> "PQexec" or "PQsendQuery". I'm not sure why the "PQexec" access point is
> undocumented but this "\;" syntax, vis-a-vis ";" provides me that choice.

psql splits the input string on semicolons and submits each resulting
part separately using PQexec. Since \; defeats the splitting efforts,
what happens is that the whole tihng is submitted via PQexec() as a
single unit instead. PQsendQuery is never used by psql.

Now PQexec is documented to return only the last resultset if you send
more than one query through it; so that part seems okay since it's been
documented this way forever. However, psql is not documented to use
PQexec, it just happens to use it.

Now, I think requesting psql not to split query strings is a good
feature, but having it depend on using \; instead of ; seems way too
obscure. If we want to offer that choice, I propose we do it via some
properly designed mechanism rather than being a random emergent
characteristic falling out of a bunch of historical coincidences.

--
Álvaro Herrera http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services