Re: plpgsql.consistent_into - Mailing list pgsql-hackers

On 1/12/14, 7:47 AM, Pavel Stehule wrote:

2014/1/12 Marko Tiikkaja <marko@joh.to>

Greetings fellow elephants,

I would humbly like to submit for your consideration my proposal for
alleviating pain caused by one of the most annoying footguns in PL/PgSQL:
the behaviour of SELECT .. INTO when the query returns more than one row.
  Some of you might know that no exception is raised in this case (as
opposed to INSERT/UPDATE/DELETE .. INTO, all of them yielding
TOO_MANY_ROWS), which can hide subtle bugs in queries if during testing the
query always returns only one row or the "correct" one happens to be picked
up every time.  Additionally, the row_count() after execution is always
going to be either 0 or 1, so even if you want to explicitly guard against
potentially broken queries, you can't do so!

It is not bad and, sure, - it is very useful and important

but - it is a redundant to INTO STRICT clause. When you use it, then you
change a INTO behaviour. Is not better to ensure STRICT option than hidden
redefining INTO?

That only works if the query should never return 0 rows either.  If you want to allow for missing rows, STRICT is out of the question.

Option INTO (without STRICT clause) is not safe and we should to disallow.
I see a three states (not only two)

a) disallow INTO without STRICT (as preferred for new code)
b) implicit check after every INTO without STRICT
c) without check

these modes should be: "strict_required", "strict_default", "strict_legacy"

I can't get excited about this.  Mostly because it doesn't solve the problem I'm having.

It is important to be able to execute queries with INTO which might not return a row.  That's what FOUND is for.

So I added the following compile-time option:


set plpgsql.consistent_into to true;

This name is not best (there is not clean with it a into should be
consistent)

I agree, but I had to pick something.  One of the three hard problems in CS..

Is question, if this functionality should be enabled by GUC to be used for
legacy code (as protection against some kind of hidden bugs)

This topic is interesting idea for me - some checks can be pushed to
plpgsql_check (as errors or warnings) too.

Generally I like proposed functionality, just I am not sure, so hidden
redefining INTO clause (to INTO STRICT) is what we want. We can do it (but
explicitly). I don't know any situation where INTO without STRICT is valid.
Introduction of STRICT option was wrong idea - and now is not way to back.

Note that this is different from implicitly STRICTifying every INTO, like I said above.


Regards,
Marko Tiikkaja