Můžete to udělat takto
declare @T table (ID int, startDateTime datetime, endDateTime datetime)
insert into @T values
( 1 , '2010-01-01 10:30:00' , '2010-01-01 11:00:00'),
( 2 , '2010-01-01 10:30:00' , '2010-01-01 11:30:00'),
( 3 , '2010-01-01 11:00:00' , '2010-01-01 11:30:00'),
( 4 , '2010-01-01 11:00:00' , '2010-01-01 12:00:00'),
( 5 , '2010-01-01 11:30:00' , '2010-01-01 12:00:00')
declare @startDateTime datetime
declare @endDateTime datetime
set @startDateTime = '2010-01-01 11:00:00'
set @endDateTime = '2010-01-01 11:30:00'
select *
from @T
where
startDateTime < @endDateTime and
endDateTime > @startDateTime