CREATE OR REPLACE FUNCTION GET_SEX(id_card IN VARCHAR(50))
 RETURN CHAR(2)AS v_sex CHAR(2);
BEGIN
  IF to_number(substr(id_card, 17, 1)) %2 = 1 THEN
            v_sex := '男';
        ELSE
            v_sex := '女';
  END IF;
        RETURN v_sex;
END;

估计是空格部分有不可见的字符