SQL> select to_char(to_date('20060831','yyyymmdd') + interval '1' month,'yyyymmdd') from dual ;

select to_char(to_date('20060831','yyyymmdd') + interval '1' month,'yyyymmdd') from dual

ORA-01839: 指定月份的日期无效

SQL> select to_char(to_date('20060831','yyyymmdd') + interval '2' month,'yyyymmdd') from dual ;

TO_CHAR(TO_DATE('20060831','YY
------------------------------
20061031

SQL> select to_char(to_date('20060831','yyyymmdd') + interval '3' month,'yyyymmdd') from dual ;

select to_char(to_date('20060831','yyyymmdd') + interval '3' month,'yyyymmdd') from dual

ORA-01839: 指定月份的日期无效

SQL> select to_char(to_date('20060831','yyyymmdd') + interval '4' month,'yyyymmdd') from dual ;

TO_CHAR(TO_DATE('20060831','YY
------------------------------
20061231

SQL> select to_char(to_date('20060131','yyyymmdd') + interval '1' month,'yyyymmdd') from dual ;

select to_char(to_date('20060131','yyyymmdd') + interval '1' month,'yyyymmdd') from dual

ORA-01839: 指定月份的日期无效

SQL> select to_char(to_date('20060130','yyyymmdd') + interval '1' month,'yyyymmdd') from dual ;

select to_char(to_date('20060130','yyyymmdd') + interval '1' month,'yyyymmdd') from dual

ORA-01839: 指定月份的日期无效

SQL> select to_char(to_date('20060129','yyyymmdd') + interval '1' month,'yyyymmdd') from dual ;

select to_char(to_date('20060129','yyyymmdd') + interval '1' month,'yyyymmdd') from dual

ORA-01839: 指定月份的日期无效

SQL> select to_char(to_date('20060128','yyyymmdd') + interval '1' month,'yyyymmdd') from dual ;

TO_CHAR(TO_DATE('20060128','YY
------------------------------
20060228


如果是日期中的日在下一（n）个月中不存在，就会报出错误，而用add_months是没有问题的。
以上问题在9i和10g上都试验过！