SELECT u.user_id, u.username, g.group_name  FROM users u, user_groups ug,
groups g WHERE u.user_id = ug.user_id AND ug.group_id = g.group_id

<hibernate-mapping>
    <class name="model.Users" table="users">
    <id name="user_id">
        <generator class="identity" />
    </id>
    <property name="username" type="string" />
    <property name="first_name" type="string" />
    <property name="middle_name" type="string" />
    <property name="last_name" type="string" />
    <property name="password" type="string" />
    <set name="groups" table="user_groups" inverse="false" lazy="true" fetch="select" cascade="all" >
        <key>
            <column name="user_id" not-null="true" />
        </key>
        <many-to-many entity-name="model.Groups">
            <column name="group_id" not-null="true" />
        </many-to-many>
    </set>
    <!--one to many users -> incydent -->
    <set name="incydents" table="incydents" inverse="true" lazy="true" fetch="select">
            <key>
                <column name="user_id" not-null="true" />
            </key>
            <one-to-many class="model.Incydents" />
    </set>
    <!-- one to many users -> incydent -->
    </class>
</hibernate-mapping>

Groups.hbm.xml

<hibernate-mapping>
    <class name="model.Groups" table="groups">
  <id name="group_id">
      <column name="group_id" />
      <generator class="identity" />
  </id>
  <property name="group_name" />
  <property name="group_desc" />
  <set name="users" table="user_groups" inverse="true" lazy="true" fetch="select">
      <key>
          <column name="group_id" not-null="true" />
      </key>
      <many-to-many entity-name="model.Users">
          <column name="user_id" not-null="true" />
      </many-to-many>
  </set>
  </class>
</hibernate-mapping>

<hibernate-mapping>
    <class name="model.Incydents" table="incydents">
        <id name="inc_id" column="inc_id">
            <generator class="identity" /> <!--native-->
        </id>
        <property name="inc_desc" />
        <many-to-one name="users" class="model.Users" fetch="select">
            <column name="user_id" not-null="true" />
        </many-to-one>
    </class>
</hibernate-mapping>