Re: Function overloading

On Sat, 9 Dec 2000, Tom Lane wrote:

> Rynell Wesson <rwesson(at)cs(dot)utexas(dot)edu> writes:
> > I keep getting the following error.
>
> > psql:fdm:11: ERROR: Function 'foo(unknown, unknown)' does not exist
>
> That could only come out when you write
>
> select foo('string', 'string')
>
> and there is more than one possible candidate for foo(). The thing to
> realize here is that Postgres does not assume that 'string' is a string.
> Rather, it is a literal of as-yet-undetermined type. If the particular
> foo() function can be identified uniquely, then the system can infer
> what type the unknown-type literal should be converted to. Otherwise
> it gets unhappy.
>
> In the example you've given,
> select foo(text('testing'), text('testing'));
> ought to work fine to select the foo(text,text) function. It does work
> when I try it. I wonder whether you are looking for the problem in the
> wrong place. Is it possible that the error report is actually coming
> from trying to evaluate the function body? What did you put in the
> body, anyway?

Unless I missed something, the function bodies do not appear to be the
problem. They have both been tested seperately without any problems. It
seems as if there is a problem with the compiler's semantic analysis
phase. Here are the function bodies.

CREATE FUNCTION foo(text, text)
RETURNS NUMERIC AS '

DECLARE

p_qstn ALIAS FOR $1;
p_fname ALIAS FOR $2;

v_fid foq.fid%TYPE;
v_qid foq.qid%TYPE;
v_qnum foq.qnum%TYPE;

BEGIN

SELECT id INTO v_qid FROM qwert WHERE qstn = p_qstn;
SELECT id, nqs INTO v_fid, v_qnum FROM farm
WHERE name = p_fname;
v_qnum := v_qnum + 1;

UPDATE farm SET nqs = nqs + 1
WHERE name = p_fname;

INSERT INTO foq (fid, qid, qnum)
VALUES (v_fid, v_qid, v_qnum);

RETURN 0;

END;'
LANGUAGE 'plpgsql';

CREATE FUNCTION foo(int4, int4)
RETURNS NUMERIC AS '

DECLARE

p_qid ALIAS FOR $1;
p_fid ALIAS FOR $2;

v_qnum foq.qnum%TYPE;

BEGIN

SELECT nqs INTO v_qnum FROM farm WHERE id = p_fid;
v_qnum := v_qnum + 1;

UPDATE farm SET nqs = nqs + 1
WHERE id = p_fid;

INSERT INTO foq (fid, qid, qnum)
VALUES (p_fid, p_qid, v_qnum);

RETURN 0;

END;'
LANGUAGE 'plpgsql';

>
> BTW, Postgres 7.1 has been tweaked to be more willing to assume that
> an unidentified-type literal is a string datatype, when it can't make
> a unique decision otherwise. So in 7.1 you'll get the result you
> expected from "select foo('string', 'string')". But the form with
> the explicit casts should have worked anyway.
>
> regards, tom lane
>