Thread: Fwd: Need help in porting Oracle PL/SQL's OUT paramater based procedures

Gurjeet Singh wrote:
> that is, not passing anything for the OUT or INOUT parameters. This works
> fine for a simple SELECT usage, but does not play well when this function is
> to be called from another function, (and assuming that it'd break the
> application code too, which uses Oracle syntax of calling functions)!
>
> I have a simple function f() which I'd like to be ported in such a way that
> it works when called from other plpgsql code, as well as when the
> application uses the Oracle like syntax. Here's a sample usage of the
> function f() in Oracle:

If you really want Oracle-compatible functions I think there's a company
that might sell you a solution :-)

However, failing that you'll want an example of OUT parameters in
PostgreSQL code - see below. The main thing to remember is that the OUT
is really just a shortcut way of defining a record type that gets
returned. It's nothing like passing by reference in <insert real
programming language here>.


BEGIN;

CREATE OR REPLACE FUNCTION f1(IN a integer, INOUT b integer, OUT c
integer) RETURNS RECORD AS $$
BEGIN
    c := a + b;
    b := b + 1;
    -- No values in RETURN
    RETURN;
END;
$$ LANGUAGE plpgsql;

CREATE OR REPLACE FUNCTION f2() RETURNS boolean AS $$
DECLARE
    a integer := 1;
    b integer := 2;
    c integer := -1;
    r RECORD;
BEGIN
    r := f1(a, b);
    -- Original variables unaffected
    RAISE NOTICE 'a=%, b=%, c=%', a,b,c;
    -- OUT params are here instead
    RAISE NOTICE 'r.b=%, r.c=%', r.b, r.c;

    -- This works, though notice we treat the function as a row-source
    SELECT (f1(a,b)).* INTO b,c;
    RAISE NOTICE 'a=%, b=%, c=%', a,b,c;

    RETURN true;
END;
$$ LANGUAGE plpgsql;

SELECT f2();

ROLLBACK;

--
  Richard Huxton
  Archonet Ltd

Removed -hackers from the mailing-lists. Just noticed it, and I think
this is probably fine on the general list.

Gurjeet Singh wrote:
> On Thu, Feb 12, 2009 at 6:18 PM, Richard Huxton <dev@archonet.com> wrote:

>> CREATE OR REPLACE FUNCTION f1(IN a integer, INOUT b integer, OUT c
>> integer) RETURNS RECORD AS $$

> You see, you did not pass the third (OUT) parameter when calling the
> function:
>
>    r := f1(a, b);
>
> This differs from Oracle syntax where you _need_ to pass the third
> parameter.

That's because pl/pgsql isn't pl/sql. If you want to keep close, you can
just declare "c" as INOUT.

The original problem was that it was a pain to declare types for every
function that returned more than just a simple scalar. The alternative
was to say you returned RECORD, but then you needed to list column-names
when calling the function. Finally, IN/OUT/INOUT was abused to provide
an implicit record-type declaration for you. It's convenient for simple
cases, but it's not actually what I think of as IN/OUT parameters.

> And what if the Oracle function actually returns a value too? How do we
> handle that in the application, because we can't declare RECORD vars in
> Java/perl/python etc.

You can always do something like: SELECT b,c FROM f1(1, 2);


Realistically, I don't think you're going to get one set of queries
running against both RDBMS.

--
  Richard Huxton
  Archonet Ltd