I am using Jboss 4.0.3SP1.

I have a Employee table.(id, name, addrId).

Employee {
...
@OneToOne
@JoinColumn(name="addrId")
Address getAddress() {...}

String getName() {...}
}

I did not use @index on any properties.

After deploy,

mysql > show index from employee;

+------------+------------+---------------------------+--------------+---
| Table Non_unique | Key_name | Column_name
+------------+------------+---------------------------+--------------+---
| employee| 0 | PRIMARY | id
| employee| 0 | name | name
| employee| 0 | addrId | addrId
| employee| 1 | FKE5C254025FFF52BB | addrId

It seems that Hibernate has created 4 indexes.
Why create two indexes for addrId?
Is it useful to create index for addrId?


If I add index on name,

@Index(name="employee_name_idx")
String getName() {...}

The index on name will be created, ignoring existing index (on name).
I am confused. Please help me understand. It would be very nice. Thanks!