0007793: substr overloading for postgresql not working

Description

In the Oracle native substr function, when an index of 0 is received as first position of the string, it turns it to a 1. In postgresql, if a 0 is received, then no value is returned as first character, so there exists a function called substr in OpenbravoERP that tries to emulate this behavior:

-- Function: substr(character varying, numeric, numeric)
CREATE OR REPLACE FUNCTION substr(character varying, numeric, numeric)
  RETURNS character varying AS
$BODY$
BEGIN
return substr($1,CAST((CASE $2 WHEN 0 THEN 1 ELSE $2 END) AS INTEGER), CAST($3 AS INTEGER));
END;
$BODY$
  LANGUAGE 'plpgsql' IMMUTABLE
  COST 100;

Actually, this is not working, because when a substr function is invoked, then the postgresql native one is executed. The difference between both functions is in the parameter types:

The one in Openbravo ERP:
substr(character varying, numeric, numeric)

Included in Postgresql catalog:
substr(text, integer, integer)
as well as
substr(bytea, integer)
substr(text, integer)
substr(bytea, integer, integer)

substr function must be re-defined

Steps To Reproduce

In Oracle:

select substr('123',0,2) from dual; -> 12
select substr('123',0,1) from dual; -> 1

In Postgresql:

select substr('123',0,2); -> 1
select substr('123',0,1); -> <empty string>

Issue History
Date Modified	Username	Field	Change
2009-02-24 12:10	psarobe	Type	defect => backport
2009-02-24 12:10	psarobe	fix_in_branch	=> 2.40
2009-02-24 12:11	psarobe	Assigned To	pjuvara => shuehner
2012-02-20 11:41	shuehner	Status	scheduled => closed
2012-02-20 11:41	shuehner	Resolution	open => out of date

Notes
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