mysql muestra los intervalos de tiempo disponibles y los intervalos de tiempo ocupados de la tabla

De acuerdo, MySQL puro, siempre que a uno le gusten esos trucos. Necesito una Variable que se inicialice al "Comienzo" de los períodos para mostrar, algo así como now() normalmente.

Primero solo los datos de prueba:

create table bookingEvents 
   (id int not null primary key auto_increment,
    timeBooked datetime, 
    duration int
   );


insert into bookingEvents values (null, '2013-05-13 13:22:00', 15);
insert into bookingEvents values (null, '2013-05-13 15:10:00', 45);
insert into bookingEvents values (null, '2013-05-13 19:55:00', 30);
insert into bookingEvents values (null, '2013-05-14 03:22:00', 15);
insert into bookingEvents values (null, '2013-05-14 08:19:00', 15);

Luego inicializando el "control deslizante":

set @timeSlider='2013-05-10 00:00:00';

Luego seleccione:

select if (d.name = 'Free', @timeSlider, b.timeBooked) as free_from,
       if (d.name = 'Free', b.timeBooked, @timeSlider := b.timeBooked + interval b.duration minute) as free_until,
       d.name as Free
from (select 1 as place, 'Free' as name union select 2 as place, 'Booked' as name) d 
inner join bookingEvents b 
having free_from < free_until
order by b.timeBooked, d.place;

Resultado:

+---------------------+---------------------+--------+
| free_from           | free_until          | Free   |
+---------------------+---------------------+--------+
| 2013-05-10 00:00:00 | 2013-05-13 13:22:00 | Free   |
| 2013-05-13 13:22:00 | 2013-05-13 13:37:00 | Booked |
| 2013-05-13 13:37:00 | 2013-05-13 15:10:00 | Free   |
| 2013-05-13 15:10:00 | 2013-05-13 15:55:00 | Booked |
| 2013-05-13 15:55:00 | 2013-05-13 19:55:00 | Free   |
| 2013-05-13 19:55:00 | 2013-05-13 20:25:00 | Booked |
| 2013-05-13 20:25:00 | 2013-05-14 03:22:00 | Free   |
| 2013-05-14 03:22:00 | 2013-05-14 03:37:00 | Booked |
| 2013-05-14 03:37:00 | 2013-05-14 08:19:00 | Free   |
| 2013-05-14 08:19:00 | 2013-05-14 08:34:00 | Booked |
+---------------------+---------------------+--------+

Si tiene una marca de tiempo de finalización determinada, debe preestablecerla como @timeMaximum

set @timeSlider='2013-05-10 00:00:00';
set @timeMaximum='2013-05-14 08:35:00';


select if (d.name = 'Free', @timeSlider, b.timeBooked) as free_from,
       if (d.name = 'Free', b.timeBooked, @timeSlider := b.timeBooked + interval b.duration minute) as free_until,
       d.name as Free
from (select 1 as place, 'Free' as name union select 2 as place, 'Booked' as name ) as d 
inner join bookingEvents b 
having free_from < free_until
union select @timeSlider as free_from, @timeMaximum as free_until, 'Free' as Free
from (select 1) as d
where @timeSlider < @timeMaximum

order by free_from, free_until
;