Creating sql indexes via Hibernate

The definition of a database index  from wikipedia is as follows:
A database index is a data structure that improves the speed of data retrieval operations on a database table at the cost of slower writes and increased storage space.
Indexes can be created using one or more columns of a database table, providing the basis for both rapid random lockups and efficient access of ordered records
Indexes play an important role in optimizing database performance.The indexes can be specified as a part of the hbm files. To create an index on the FIRST_NAME column of user table, we need to add the index attribute to the first_name attribute.

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
        "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd" >
<hibernate-mapping package="com.sql.index">
    <class name="User">
        <id name="id" type="long">
            <generator class="native" />
        </id>
        <property name="firstName">
            <column name="FIRST_NAME" index="IDX_FIRST_NAME"/>
        </property>
        <property name="lastName">
            <column name="LAST_NAME" />
        </property>

    </class>
</hibernate-mapping>

On start up, the hbm2ddl tool generated the following index creation statement:

create index IDX_FIRST_NAME on User (FIRST_NAME)

It is also possible to create multi-column indexes using the same property. For example, if we need to create an Index on the basis of first_name and last_name, this can be done by setting the same index name on both columns. The modified hbm is as below:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
        "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd" >
<hibernate-mapping package="com.sql.index">
    <class name="User">
        <id name="id" type="long">
            <generator class="native" />
        </id>
        <property name="firstName">
            <column name="FIRST_NAME" index="IDX_NAME" />
        </property>
        <property name="lastName">
            <column name="LAST_NAME" index="IDX_NAME" />
        </property>

    </class>
</hibernate-mapping>

The generated SQL is as follows:

create index IDX_NAME on User (FIRST_NAME, LAST_NAME)