SQL Select Records in a range but Not in another range

Question

Dear All
I would like to know the best method to do the following task.
There are records of meeting room usage
room                        start_time
Room A                2014-08-30 16:55:00.000
Room C                      2014-08-30 13:20:00.000
Room B                      2014-08-29 21:45:00.000
Room A                      2014-08-29 22:00:00.000 
I would like to get the rooms used at a range (e.g. 2014-08-30) but cannot be used in another range (e.g. 2014-08-29 or before)
The result should be Room C only.
My apporach is as follows
SELECT room FROM RoomUsage
WHERE start_time >= '2014-08-30 00:00:00' AND start_time <= '2014-08-30 23:59:59'
AND room NOT IN (
SELECT room FROM RoomUsage
     WHERE start_time < '2014-08-30 00:00:00'
Is there any better and simple approach to achieve the same result?
Thank you
Best Regards
swivan

Answer 1

I tend to use EXCEPT or NOT EXISTS for this kind of thing as I find them more intuitive.  I also tend
not to use Not In for JOINs due to its well-known problem with NULLs, ie if there is a NULL in the inner resultset the query short-circuits and you get no records.  I therefore prefer to use In / Not In for
short lists eg Not In ( 'a', 'b', 'c' ).
See for yourself:
IF OBJECT_ID('tempdb..#roomUsage') IS NOT NULL DROP TABLE #roomUsage
CREATE TABLE #roomUsage ( room VARCHAR(20) NOT NULL, start_time DATETIME2 NOT NULL )
INSERT INTO #roomUsage
VALUES
( 'Room A', '2014-08-30 16:55:00.000' ),
( 'Room C', '2014-08-30 13:20:00.000' ),
( 'Room B', '2014-08-29 21:45:00.000' ),
( 'Room A', '2014-08-29 22:00:00.000' )
SELECT room
FROM #roomUsage
WHERE start_time >= '2014-08-30 00:00:00' AND start_time <= '2014-08-30 23:59:59'
EXCEPT
SELECT room
FROM #roomUsage
WHERE start_time < '2014-08-30 00:00:00'
SELECT room FROM #roomUsage
WHERE start_time >= '2014-08-30 00:00:00' AND start_time <= '2014-08-30 23:59:59'
AND room NOT IN (
SELECT room FROM #roomUsage
WHERE start_time < '2014-08-30 00:00:00'
-- Oops
SELECT room FROM #roomUsage
WHERE start_time >= '2014-08-30 00:00:00' AND start_time <= '2014-08-30 23:59:59'
AND room NOT IN (
SELECT room FROM #roomUsage
WHERE start_time < '2014-08-30 00:00:00'
UNION ALL
SELECT NULL