帮忙看看，为什么是这样的结果

kgong

mysql> create table test(
    -> id int not null auto_increment primary key,
    -> name char(10),
    -> title varchar(20),
    -> fulltext(name,title))type=myisam;
Query OK, 0 rows affected, 1 warning (0.14 sec)

mysql> select * from test;
+----+------+-------+
| id | name | title |
+----+------+-------+
| 1  | a    | b     |
| 2  | a    | aa    |
+----+------+-------+
2 rows in set (0.00 sec)

mysql>select * from test where match(name,title)against('+a -b' in boolean mode);
Empty set (0.00 sec)

没有找到任何记录，请问该如何写呢？