Re: Is a function to a 1-component record type undeclarable? - Mailing list pgsql-hackers

On 11/22/21 11:59, Pavel Stehule wrote:
> And if we allow RETURNS RECORD, then there will be new inconsistency
> between OUT variables and RETURNS TABLE

I don't really see it as a new inconsistency, so much as the same old
inconsistency but with an escape hatch if you really mean the other thing.

I take the consistency you speak of here to be "anything you can say with
OUT parameters is equivalent to something you can say with RETURNS TABLE."
That is tidy, but I don't think it suffers much if it becomes "everything
you can say with RETURNS TABLE is something you can equivalently say with
OUT parameters, but there is one thing for historical reasons you can't say
with RETURNS TABLE, and if you need to say that, with OUT params you can."

> Do you have some real use cases, where proposed functionality will carry
> some benefit?

The most general might be a refactoring situation where you start with
something producing a two-component record and one of those goes away, and
you want to make the minimally invasive changes. Going through containing
queries to add or remove row() or .foo would be more invasive.

I often am coming from the position of a PL maintainer, where my aim
is to present an accurate picture of what is going on in PostgreSQL
to people who are thinking in Java, and to support them with language
constructs that will do what they expect. I happened to notice today
that I am generating SQL that won't succeed if a Java function declares
a one-component record result. Ok, so that's a bug I have to fix, and
document what the real behavior is. Beyond that, if I could also say
"if a one component record is really what you want, then write *this*",
I think that would be good.


It seems like something that would entail a very easy change in the docs.
The paragraph that now says

  When there are OUT or INOUT parameters, the RETURNS clause can be
  omitted. If present, it must agree with the result type implied by
  the output parameters: RECORD if there are multiple output parameters,
  or the same type as the single output parameter.

it could simply say

  When there are OUT or INOUT parameters, the RETURNS clause can be
  omitted. If present, it must agree with the result type implied by
  the output parameters: always RECORD if there are multiple output
  parameters. For exactly one output parameter, there is a choice:
  the same type as the single output parameter (which is the default
  if the clause is omitted), or RECORD if the function should really
  return a composite type with one component.

Regards,
-Chap