PostgreSQL模仿Oracle的instr函数

--
-- instr functions that mimic Oracle's counterpart
-- Syntax: instr(string1, string2, [n], [m]) where [] denotes optional parameters.
--
-- 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).
--

CREATE FUNCTION instr(varchar, varchar) RETURNS integer AS $$
DECLARE
pos integer;
BEGIN
pos:= instr($1, $2, 1);
RETURN pos;
END;
$$ LANGUAGE plpgsql STRICT IMMUTABLE;

CREATE FUNCTION instr(string varchar, string_to_search varchar, beg_index integer)
RETURNS integer AS $$
DECLARE
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 STRICT IMMUTABLE;

CREATE FUNCTION instr(string varchar, string_to_search varchar,
beg_index integer, occur_index integer)
RETURNS integer AS $$
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;
$$ LANGUAGE plpgsql STRICT IMMUTABLE;