instr(character varying, character varying, integer, integer)

DECLARE

    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;