Porting from Oracle PL/SQL:

--
-- instr functions that mimic Oracle's counterpart
-- Syntax: instr(string1,string2,[n],[m]) where [] denotes optional params.
--
-- Searches string1 beginning at the nth character for the mth
-- occurrence of string2. If n is negative, search backwards. If m is
-- not passed, assume 1 (search starts at first character).
--
-- by Roberto Mello (rmello@fslc.usu.edu)
-- modified by Robert Gaszewski (graszew@poland.com)
-- Licensed under the GPL v2 or later.
--

CREATE FUNCTION instr(VARCHAR,VARCHAR) RETURNS INTEGER AS '
DECLARE
pos integer;
BEGIN
pos:= instr($1,$2,1);
RETURN pos;
END;
' LANGUAGE 'plpgsql';


CREATE FUNCTION instr(VARCHAR,VARCHAR,INTEGER) RETURNS INTEGER AS '
DECLARE
string ALIAS FOR $1;
string_to_search ALIAS FOR $2;
beg_index ALIAS FOR $3;
pos integer NOT NULL DEFAULT 0;
temp_str VARCHAR;
beg INTEGER;
length INTEGER;
ss_length INTEGER;
BEGIN
IF beg_index > 0 THEN

temp_str := substring(string FROM beg_index);
pos := position(string_to_search IN temp_str);

IF pos = 0 THEN
RETURN 0;
ELSE
RETURN pos + beg_index - 1;
END IF;
ELSE
ss_length := char_length(string_to_search);
length := char_length(string);
beg := length + beg_index - ss_length + 2;

WHILE beg > 0 LOOP
temp_str := substring(string FROM beg FOR ss_length);
pos := position(string_to_search IN temp_str);

IF pos > 0 THEN
RETURN beg;
END IF;

beg := beg - 1;
END LOOP;
RETURN 0;
END IF;
END;
' LANGUAGE 'plpgsql';

--
-- Written by Robert Gaszewski (graszew@poland.com)
-- Licensed under the GPL v2 or later.
--
CREATE FUNCTION instr(VARCHAR,VARCHAR,INTEGER,INTEGER) RETURNS INTEGER AS '
DECLARE
string ALIAS FOR $1;
string_to_search ALIAS FOR $2;
beg_index ALIAS FOR $3;
occur_index ALIAS FOR $4;
pos integer NOT NULL DEFAULT 0;
occur_number INTEGER NOT NULL DEFAULT 0;
temp_str VARCHAR;
beg INTEGER;
i INTEGER;
length INTEGER;
ss_length INTEGER;
BEGIN
IF beg_index > 0 THEN
beg := beg_index;
temp_str := substring(string FROM beg_index);

FOR i IN 1..occur_index LOOP
pos := position(string_to_search IN temp_str);

IF i = 1 THEN
beg := beg + pos - 1;
ELSE
beg := beg + pos;
END IF;

temp_str := substring(string FROM beg + 1);
END LOOP;

IF pos = 0 THEN
RETURN 0;
ELSE
RETURN beg;
END IF;
ELSE
ss_length := char_length(string_to_search);
length := char_length(string);
beg := length + beg_index - ss_length + 2;

WHILE beg > 0 LOOP
temp_str := substring(string FROM beg FOR ss_length);
pos := position(string_to_search IN temp_str);

IF pos > 0 THEN
occur_number := occur_number + 1;

IF occur_number = occur_index THEN
RETURN beg;
END IF;
END IF;

beg := beg - 1;
END LOOP;

RETURN 0;
END IF;
END;
' LANGUAGE 'plpgsql';