public class Department
{
    departmentId;
    name;
    country;
    type;
}

public class ItDepatment extends Department
{
    itDeparmentCode;
    description;
    billingType;
   //Many other fields
}

<select id="getDepartment" resultMap="departmentMap">
  select * from Department
</select>

<resultmap id="departmentMap" type="Department">
  <result property="departmentId" column="ID"/>
  <result property="name" column="NAME"/>
  <result property="country" column="COUNTRY"/>
  <discriminator javaType="java.lang.String" column="TYPE">
    <case value="IT" resultmap="itDepartmentResultmap"/>
    <case value="SALES" resultmap="salesDepartmentResultmap"/>
  </discriminator>
</resultmap>

<resultmap id="itDepartmentResultmap" type="ItDepatment">
   <result property="itDeparmentCode" column="CODE"/>
   <result property="description" column="DESCRIPTION"/>
   <result property="billingType" column="BILLING_TYPE"/>
</resultmap>

<select id="getItDepartment" resultMap="itDepartmentResultmap">
      select * from ItDepartment where id=#{departmentId}
</select>