MSSQL Datediff for time slot scheduling

Posted on 2009-06-30
Last Modified: 2012-05-07
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).
SELECT timeslotid, 
datepart(hh, convert(smalldatetime, timeslotstart, 14)) as StartTime, 
convert(smalldatetime, timeslotend, 14) as EndTime,
WHEN datepart(hh, convert(smalldatetime, timeslotstart, 14)) 
(SELECT datepart(hh, convert(smalldatetime, timeslotstart, 14)) 
from dbo.TimeSlots WHERE TimeSlotID = 2)
(SELECT datepart(hh, convert(smalldatetime, timeslotend, 14))from dbo.TimeSlots WHERE TimeSlotID = 2)
END as StartTime,
WHEN convert(smalldatetime, timeslotend, 14) 
(SELECT  convert(smalldatetime, timeslotstart, 14) 
from dbo.TimeSlots WHERE TimeSlotID = 2)
(SELECT convert(smalldatetime, timeslotend, 14)from dbo.TimeSlots WHERE TimeSlotID = 2)
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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Question by:GLIanimal
LVL 59

Accepted Solution

Kevin Cross earned 500 total points
ID: 24746127
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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Author Closing Comment

ID: 31598338
Had to add IN and count for multiple values, but all in all thanks!

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