Re: plpgsql.consistent_into

2014/1/14 Florian Pflug <fgp(at)phlo(dot)org>

> On Jan14, 2014, at 00:52 , Marko Tiikkaja <marko(at)joh(dot)to> wrote:
> > When I've worked with PL/PgSQL, this has been a source of a few bugs that
> > would have been noticed during testing if the behaviour of INTO wasn't as
> > dangerous as it is right now.
>
> The question is, how many bugs stemmed from wrong SQL queries, and what
> percentage of those would have been caught by this? The way I see it, there
> are thousands of ways to screw up a query, and having it return multiple
> rows instead of one is just one of them.
>
> > Yes, it breaks backwards compatibility, but that's why there's a nice
> GUC.
>
> Which doesn't help, because the GUC isn't tied to the code. This *adds*
> an error case, not remove one - now, instead of getting your code correct,
> you *also* have to get the GUC correct. If you even *know* that such a GUC
> exists.
>
> > If we're not going to scrap PL/PgSQL and
> > start over again, we are going to have to do changes like this to make
> the
> > language better. Also I think that out of all the things we could do to
> > break backwards compatibility, this is closer to "harmless" than "a pain
> > in the butt".
>
> I very strongly believe that languages don't get better by adding a
> thousand
> little knobs which subtly change semantics. Look at the mess that is PHP -
> we absolutely, certainly don't want to go there. The most important rule in
> language design is in my opinion "stick with your choices". C, C++ and JAVA
> all seem to follow this, and it's one of the reasons these languages are
> popular for big projects, I think.
>
> The way I see it, the only OK way to change existing behaviour is to have
> the concept of a "language version", and force code to indicate the
> language
> version it expects. The important thing is that the language version is an
> attribute of code, not some global setting that you can change without ever
> looking at the code it'd affect.
>
> So if we really want to change this, I think we need to have a
> LANGUAGE_VERSION attribute on functions. Each time a major postgres release
> changes the behaviour of one of the procedural languages, we'd increment
> that language's version, and enable the old behaviour for all functions
> tagged with an older one.
>

I dislike this proposal

too enterprise, too complex, too bad - after ten years we can have a ten
language versions and it helps nothing.

return back to topic

a) there is agreement so we like this functionality as plpgsql option

b) there is no agreement so we would to see this functionality as default
(or in near future)

@b is a topic, that we should not to solve and it is back again and again.
Sometimes we have success, sometimes not. Temporal GUC is not enough
solution for some people.

So my result - @a can be implement, @b not

and we can continue in other thread about SELECT INTO redesign and about
possibilities that we have or have not. It is about personal perspective -
someone can thinking about missing check after INTO as about feature, other
one can see it as bug. My opinion - it is a bug with possible ambiguous
result and possible negative performance impacts. Probably we can precise a
doc about wrong and good usage SELECT INTO clause.

I am working on plpgsql_debug extension and I am thinking so I am able
(with small change in plpgsql executor) implement this check as extension.
So it can be available for advanced users (that will has a knowledge about
additional plpgsql extensions).

Regards

Pavel

regards

Pavel

>
> best regards,
> Florian Pflug
>
>
>
>
>
>
>