自定义函数，替换字符串中指定位置的字符

CREATE OR REPLACE FUNCTION REPLACE_POSITION(STR_IN   VARCHAR2,
POSITION INTEGER,
NEW_CHAR VARCHAR2)
/*
用于替换字符串中指定位置的字符的函数
*/
RETURN VARCHAR2 IS
RESULT VARCHAR2(32000);
STR1   VARCHAR2(32000);
STR2   VARCHAR2(10);
STR3   VARCHAR2(32000);
BEGIN
IF POSITION <= LENGTHB(STR_IN) AND POSITION > 0 THEN
STR1   := SUBSTR(STR_IN, 1, POSITION - 1);
STR2   := SUBSTR(STR_IN, POSITION, 1);
STR3   := SUBSTR(STR_IN, POSITION + 1, LENGTHB(STR_IN));
STR2   := REPLACE(STR2, STR2, NEW_CHAR);
RESULT := STR1 || STR2 || STR3;
ELSE
RESULT := STR_IN;
END IF;
RETURN(RESULT);
END REPLACE_POSITION;