INTERVAL YEAR TO MONTH数据类型是用来存储两个时间戳之间的时间差，这个差值精确到时间的年和月。

oracle文档里这样描述：

Stores a period of time in years and months, where year_precision is the number of digits in the YEAR datetime field. Accepted values are 0 to 9. The default is 2. The size is fixed at 5 bytes.

Oracle语法:
INTERVAL 'integer [- integer]' {YEAR | MONTH} [(precision)][TO {YEAR | MONTH}]

示例：(参考)

SQL> CREATE TABLE coupons (
  2    coupon_id INTEGER,
  3    name VARCHAR2(30),
  4    duration INTERVAL YEAR(3) TO MONTH
  5  );

Table created.

SQL>
SQL>
SQL> INSERT INTO coupons (coupon_id, name, duration) VALUES (1, '$1 off Z Files', INTERVAL '1' YEAR);

1 row created.

SQL> INSERT INTO coupons (coupon_id, name, duration) VALUES (2, '$2 off Pop 3', INTERVAL '11' MONTH);

1 row created.

SQL> INSERT INTO coupons (coupon_id, name, duration) VALUES (3, '$3 off Modern Science', INTERVAL '14' MONTH);

1 row created.

SQL> INSERT INTO coupons (coupon_id, name, duration) VALUES (4, '$2 off Tank War', INTERVAL '1-3' YEAR TO MONTH);

1 row created.

SQL> INSERT INTO coupons (coupon_id, name, duration) VALUES (5, '$1 off Chemistry', INTERVAL '0-5' YEAR TO MONTH);

1 row created.

SQL> INSERT INTO coupons (coupon_id, name, duration) VALUES (6, '$2 off Creative Yell', INTERVAL '123' YEAR(3));

1 row created.

SQL>
SQL> SELECT * FROM coupons;

COUPON_ID NAME                           DURATION
---------- ------------------------------ ---------------------------------------------------------------------------
         1 $1 off Z Files                 +001-00
         2 $2 off Pop 3                   +000-11
         3 $3 off Modern Science          +001-02
         4 $2 off Tank War                +001-03
         5 $1 off Chemistry               +000-05
         6 $2 off Creative Yell           +123-00

6 rows selected.

SQL>
SQL>
SQL>
SQL> drop table coupons;

参考：

1、INTERVAL YEAR TO MONTH数据类型 http://www.itpub.net/thread-1023060-1-1.html

2、Data Types http://docs.oracle.com/cd/E11882_01/server.112/e17118/sql_elements001.htm

Table 3-1 Built-in Data Type Summary

3、使用INTERVAL YEAR TO MONTH类型 http://mba.shengwushibie.com/itbook/BookChapter.asp?id=34435

4、INTERVAL数据类型 http://baggio785.itpub.net/post/31233/286119