Base abstract class: 

class Vehicle {
   Long Id;
   String Color;   
}

class Car extends Vehicle {
   EngineType Engine;   
}

class Bicycle extends Vehicle {
   BicycleType BicycleType;
}

1. Single Table
Все объекты базового класса:
HQL: from Vehicle
SQL: select * from VEHICLE

Все объекты Car:
HQL: from Car
SQL: select ID, COLOR, ENGINE from VEHICLE where VEHICLE_TYPE='CAR'

2. Table per class
Все объекты базового класса:
HQL: from Vehicle
SQL: 
     select v.VEHICLE_ID, v.COLOR, c.ENGINE_TYPE, b.BICYCLE_TYPE 
	 (case when c.VEHICLE_ID IS NOT NULL THEN 'CAR'
	      when b.VEHICLE_ID IS NOT NULL THEN 'BICYCLE') VEHICLE_TYPE
	 from VEHICLE v 
	left outer join CAR c on (v.VEHICLE_ID = c.VEHICLE_ID)
	left outer join BICYCLE b on (v.VEHICLE_ID = b.VEHICLE_ID)

Все объекты Car:
HQL: from Car
SQL: 
   select v.VEHICLE_ID, v.COLOR, c.ENGINE_TYPE
    from VEHICLE v inner join CAR c on (v.VEHICLE_ID = c.VEHICLE_ID)
	
3. Table per concrete class
Все объекты базового класса:
HQL: from Vehicle
SQL:
     select 
	    CAR_ID VEHICLE_ID, 
		COLOR, 
		ENGINE_TYPE, 
		NULL BICYCLE_TYPE, 
		'CAR' VEHICLE_TYPE 
		   from CAR
	   union all
	 select 
	    BICYCLE_ID  VEHICLE_ID, 
		COLOR, 
		NULL ENGINE_TYPE, 
		BICYCLE_TYPE, 
		'BICYCLE' VEHICLE_TYPE 
		   from BICYCLE
	 
Все объекты Car:
HQL: from Car
SQL: select * from CAR