-- 实现1

CREATE FUNCTION instr(varchar, varchar) RETURNS integer AS

$$ DECLARE pos integer;

BEGIN

pos := instr($1, $2, 1);

RETURN pos;

END;

$$ LANGUAGE plpgsql STRICT IMMUTABLE;

-- 实现2

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;

ELSIF beg_index < 0 THEN

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;

ELSE

RETURN 0;

END IF;

END;

$$ LANGUAGE plpgsql STRICT IMMUTABLE;

-- 实现3

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;

ELSIF beg_index < 0 THEN

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;

ELSE

RETURN 0;

END IF;

END;

$$ LANGUAGE plpgsql STRICT IMMUTABLE;