BUG #4640: Drop leading zero in EXECUTE

The following bug has been logged online:

Bug reference:      4640
Logged by:          Eduard Deacoon
Email address:      deac@yandex.ru
PostgreSQL version: all
Operating system:   FreeBSD
Description:        Drop leading zero in EXECUTE
Details:

Hi!
EXECUTE has incorrect if one or more string have leading zero.

For example:
--- Function convert column to string with delimiter
--- $1 - TABLE with COLUMN to convert
--- $2 - COLUMN to convert
--- $3 - COLUMN for WHERE CLAUSE
--- $4 - WHERE value
--- $5 - delimeter
--- In fact: SELECT $2 FROM $1 WHERE $3 = $4 returning as string with
delimiter $5
CREATE OR REPLACE FUNCTION column_to_string(TEXT, TEXT, TEXT, TEXT, TEXT)
        RETURNS TEXT AS
E'
DECLARE
        string_res TEXT := NULL;
        r RECORD;
BEGIN
        FOR r IN EXECUTE ''SELECT '' || QUOTE_IDENT($2) || '' AS t '' || ''
                FROM '' || QUOTE_IDENT($1) || ''
                        WHERE '' || QUOTE_IDENT($3) || '' = '' ||
$4||''::TEXT'' ||
                            '' ORDER BY '' || QUOTE_IDENT($2) || '' ASC''
        LOOP
                IF r.t IS NOT NULL AND string_res IS NULL THEN
                        string_res := r.t;
                ELSEIF r.t IS NOT NULL AND string_res IS NOT NULL THEN
                        string_res := string_res || $5 || r.t;
                END IF;
        END LOOP;
        RETURN string_res;
END;
' LANGUAGE 'plpgsql' STABLE RETURNS NULL ON NULL INPUT SECURITY INVOKER;

If $4 has leading zero it does`n work :(
Context replace with ''0 || '' || $4 work only if $4 have one leading zero.
''00 || '' || $4 does`n work, ''0 || 0 ||'' || $4 - work

Nice day!