en ese sentido:
drop table if exists dates;
create table dates (d_from date, d_to date);
insert into dates values
('2014-06-15' , '2014-06-20'),
('2014-06-23' , '2014-06-27' ),
('2014-06-29' , '2014-06-30' );
select low.d_to, high.d_from, to_days(high.d_from) - to_days(low.d_to) - 1 as gap
from dates low, dates high
where high.d_from = (select min(d_from) from dates where d_from > low.d_to)
;
Lo que significa:unir la tabla a sí misma en fechas de finalización/inicio adyacentes y calcular la diferencia.
+------------+------------+------+
| d_to | d_from | gap |
+------------+------------+------+
| 2014-06-20 | 2014-06-23 | 2 |
| 2014-06-27 | 2014-06-29 | 1 |
+------------+------------+------+
