Re: [HACKERS] PL/pgSQL a great procedural language for PostgreSQL

> > Don't blame PL/pgSQL for that. There is only one bool isNull
> > pointer given to PL handlers. How should the PL handler know,
> > which of the arguments are null then? As I said on another
> > thread, the function call interface needs to get redesigned.
> Well, Jan, don't get sensitive. I love PL/pgSQL. And I had no illusions
> that it was your HANDLER causing the problem. I feel that a function
> call interface redesign is also needed. But, I do have a quick
> question, why does it matter which one is NULL if you can still obtain
> the parameters in the order they were passed why would one become NULL
> that wasn't before? I'm asking totally from ignorance here.

It might be possible, that even if *isNull is true to look at
the actual arguments given to the PL handler. For datatypes
passed by reference, a NULL value has to get passed as null
pointer. I'm not 100% sure if that is really true in all
cases where PL functions can get called, and we all know what
happens when accessing a pointer that points to something
else than a memory location. For arguments passed by value it
is totally impossible to know if it's a NULL by looking at
the value itself.

Summary is, that the PL handler cannot be sure which of the
arguments the function caller meant when calling with *isNull
= TRUE. And I decided for now to be safe and assume he meant
all.

When accessing data from a specific table, it is possible to
call the function with a complex type. This time, the
PL/pgSQL function gets the complete tuple and can look at the
information there which attributes are NULLs.

CREATE TABLE a (k integer, i integer);

CREATE FUNCTION a_i_checknull(a) RETURNS bool AS '
DECLARE
row_a ALIAS FOR $1; -- The dot-notation $1.i does not work!
BEGIN
IF row_a.k ISNULL THEN
RAISE NOTICE ''attribute k has NULL value'';
END IF;
IF row_a.i ISNULL THEN
RAISE NOTICE ''attribute i has NULL value'';
END IF;
IF row_a.k ISNULL OR row_a.i ISNULL THEN
RETURN ''t'';
END IF;
RETURN ''f'';
END;
' LANGUAGE 'plpgsql';

Jan

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