Yes! That is exactly what I have spent the last week trying to achieve.
Thanks so much.
Could I just asked if I wanted the opposite of the results would the only way be this:
SELECT
(select sum(Boiler1)
from @Energy_Centre_Availability ECA)
-
(select sum(Boiler1)
from @Energy_Centre_Availability ECA
inner join @Energy_Centre_Boiler_Maintenance_Schedule ECBMS
on ECA.t_stamp >= ECBMS.StartDate
and ECA.t_stamp <= ECBMS.EndDate)
Thanks again.