oracle 函数数值型字符判断

FUNCTION IS_INTEGER(
    IN_VARCHAR IN VARCHAR2)
  RETURN INTEGER AS FLAG INTEGER;
  I INTEGER;
BEGIN
FOR I IN 1..LENGTH(IN_VARCHAR)
LOOP
IF ASCII(SUBSTR(IN_VARCHAR,I,1))>=48 AND ASCII(SUBSTR(IN_VARCHAR,I,1))<=57
THEN
FLAG:=0;
ELSE
FLAG:=-1;
EXIT;
END IF;
END LOOP;
  RETURN FLAG;
  END IS_INTEGER;