Re: TABLE-function patch vs plpgsql

On 7/18/08, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> I've been working on the TABLE-function patch, and I am coming to the
> conclusion that it's really a bad idea for plpgsql to not associate
> variables with output columns --- that is, I think we should make
> RETURNS TABLE columns semantically just the same as OUT parameters.
> Here are some reasons:
>
> 1. It's ludicrous to argue that "standards compliance" requires the
> behavior-as-submitted. plpgsql is not specified by the SQL standard.

Yes, but it would be a good feature addition to plpgsql.
Currently there is no way to suppress the local variable
creation. The proposed behaviour would give that possibility.

> 2. Not having the parameter names available means that you don't have
> access to their types either, which is a big problem for polymorphic
> functions. Read the last couple paragraphs of section 38.3.1:
> http://developer.postgresql.org/pgdocs/postgres/plpgsql-declarations.html#PLPGSQL-DECLARATION-ALIASES
> as well as the following 38.3.2. How would you do those things with
> a polymorphic TABLE column?

This does not make sense as Postgres does not support
polymorphic table columns...

For polymorphic function arguments user should use OUT parameters.

I think thats the point - it should not be just syntactic sugar for
OUT parameters, let it be different.

> 3. Not treating the parameters as assignable variables makes RETURN NEXT
> nearly worthless in a TABLE function. Since they're not assignable,
> you can't use the parameterless form of RETURN NEXT (which'd return
> the current values of the variables). The only alternative available
> is to return a record or row variable; but there's no convenient way
> to declare such a variable, since after all the whole point here is
> that the function's output rowtype is anonymous.
>
> 4. It's a whole lot easier to explain things if we can just say that
> OUT parameters and TABLE parameters work alike. This is especially
> true when they actually *are* alike for all the other available PLs.

What other PLs do create local variables for OUT parameters?

> If we insist on the current definition then we are eventually going to
> need to kluge up some solutions to #2 and #3, which seems like make-work
> to me when we already have smooth solutions to these problems for
> OUT parameters.
>
> Comments?

I would prefer - no local vars, no polymorphism and funcname%rowtype.

Some functions are better written with OUT parameters but some
with record variable for return rows. The new behaviour would
allow picking best coding style for a function.

--
marko