MSSQL Datediff for time slot scheduling

I am in making a process for class registration. Each class has a corresponding time slot id, of which has a timeslotstart and timeslotend column. Currently they are varchar values since they only are hour & minute time slots. My issue is, when a person signs up for a class in timeslotid 2, starttime being 10 am endtime being 11am, I need to be able to remove other classes from the selection that have a starttime or endtime that is between those dates. I have something that sort of works below, but I am hoping to find something a little better. With the example below, it works for all entries except for ID 13, which has a start time of 9AM and end time of 17PM(5PM).
---------query
SELECT timeslotid, 
datepart(hh, convert(smalldatetime, timeslotstart, 14)) as StartTime, 
convert(smalldatetime, timeslotend, 14) as EndTime,
CASE 
WHEN datepart(hh, convert(smalldatetime, timeslotstart, 14)) 
between 
(SELECT datepart(hh, convert(smalldatetime, timeslotstart, 14)) 
from dbo.TimeSlots WHERE TimeSlotID = 2)
and 
(SELECT datepart(hh, convert(smalldatetime, timeslotend, 14))from dbo.TimeSlots WHERE TimeSlotID = 2)
THEN 'NOT'
ELSE 'SO'
END as StartTime,
CASE 
WHEN convert(smalldatetime, timeslotend, 14) 
between 
(SELECT  convert(smalldatetime, timeslotstart, 14) 
from dbo.TimeSlots WHERE TimeSlotID = 2)
and 
(SELECT convert(smalldatetime, timeslotend, 14)from dbo.TimeSlots WHERE TimeSlotID = 2)
THEN 'NOT'
ELSE 'SO'
END as Endtime
from dbo.timeslots
 
 
----results   bs= between start       be=between end
timeID		start			end		bs	be
1		9		1900-01-01 10:00:00	SO	NOT
2		10		1900-01-01 11:00:00	NOT	NOT
3		11		1900-01-01 12:00:00	NOT	SO
4		14		1900-01-01 15:00:00	SO	SO
5		15		1900-01-01 16:00:00	SO	SO
6		16		1900-01-01 17:00:00	SO	SO
7		9		1900-01-01 10:30:00	SO	NOT
8		9		1900-01-01 11:00:00	SO	NOT
9		10		1900-01-01 12:00:00	NOT	SO
10		10		1900-01-01 11:30:00	NOT	SO
11		14		1900-01-01 15:30:00	SO	SO
12		14		1900-01-01 16:00:00	SO	SO
13		9		1900-01-01 17:00:00	SO	SO
14		10		1900-01-01 12:00:00	NOT	SO

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GLIanimalAsked:
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Kevin CrossChief Technology OfficerCommented:
Try something like this:
+Uses a common table expression to simplify tests requiring the start and end times as datetime data type (could use view or do conversions in line).
+Filter records to time slots not equal to one already selected, in your case id #2.
+Apply or join in the data for the time slot that is selected (#2).
+Test that start is not between start and end time of selected record; however, since can start a class right as one ends backoff the endtime by a minute since between is inclusive.
+Repeat test for end time with offset to start of next class.
+Repeat with opposite side as current class may be much longer and span over already selected class.
with timeslotCTE AS (
	select timeslotid
	, cast(start as datetime) as StartTime
	, cast([end] as datetime) as EndTime
	from timeslots
) select t1.timeslotid
, convert(varchar, t1.starttime, 108) as StartTime
, convert(varchar, t1.endtime, 108) as EndTime
from timeslotCTE t1
cross apply (select starttime, endtime from timeslotCTE where timeslotid = 2) t2
where t1.timeslotid <> 2
	and t1.starttime not between t2.starttime and dateadd(mi, -1, t2.endtime)
	and t1.endtime not between dateadd(mi, +1, t2.starttime) and t2.endtime
	and t2.starttime not between t1.starttime and dateadd(mi, -1, t1.endtime)
	and t2.endtime not between dateadd(mi, +1, t1.starttime) and t1.endtime
;

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GLIanimalAuthor Commented:
Had to add IN and count for multiple values, but all in all thanks!
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Microsoft SQL Server 2005

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