The following bug has been logged online:

Bug reference: 1553
Logged by: Dan Black
Email address: dchernyshov (AT) yandex (DOT) ru
PostgreSQL version: 8.0.1
Operating system: MS Windows 2000 sp4
Description: Function arguments and table fields
Details:

1) Here is simple function

CREATE OR REPLACE FUNCTION img_update(img_name int4, img_name "varchar")
RETURNS int4 AS
$BODY$DECLARE
_imgId ALIAS FOR $1;
_imgName ALIAS FOR $2;
BEGIN
UPDATE images SET img_name = _imgName WHERE img_id = _imgId;
RETURN 0;
END$BODY$
LANGUAGE 'plpgsql' VOLATILE SECURITY DEFINER;

2) Here is simple table

CREATE TABLE images
(
img_id int4 NOT NULL DEFAULT nextval('public.images_id_seq'::text),
img_name varchar(34)
)

PROBLEM:
Function does not work

PROBLEM-SOLVING:
Need to rename function parameters, so that their names and table fields
names are unmatched.

It's not probably bug, but it's difficult-to-locate error

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Dan Black wrote:
I don't really see a way to make the error any more obvious in the
current pl/pgsql implementation, unfortunately.

-Neil

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TIP 9: the planner will ignore your desire to choose an index scan if your
joining column's datatypes do not match