Getting ranges that are not in database - sql

Question

I want to get all times that an event is not taking place for each room. The start of the day is 9:00:00 and end is 22:00:00.
What my database looks like is this:
Event EventStart EventEnd Days Rooms DayStarts
CISC 3660 09:00:00 12:30:00 Monday 7-3 9/19/2014
MATH 2501 15:00:00 17:00:00 Monday:Wednesday 7-2 10/13/2014
CISC 1110 14:00:00 16:00:00 Monday 7-3 9/19/2014
I want to get the times that aren't in the database.
ex. For SelectedDate (9/19/2014) the table should return:
Room FreeTimeStart FreeTimeEnd
7-3 12:30:00 14:00:00
7-3 16:00:00 22:00:00
ex2. SelectedDate (10/13/2014):
Room FreeTimeStart FreeTimeEnd
7-2 9:00:00 15:00:00
7-2 17:00:00 22:00:00
What I have tried is something like this:
select * from Events where ________ NOT BETWEEN eventstart AND eventend;
But I do not know what to put in the place of the space.

Answer 1

This was a pretty complex request. SQL works best with sets, and not looking at line by line. Here is what I came up with. To make it easier to figure out, I wrote it as a series of CTE's so I could work through the problem a step at a time. I am not saying that this is the best possible way to do it, but it doesn't require the use of any cursors. You need the Events table and a table of the room names (otherwise, you don't see a room that doesn't have any bookings).
Here is the query and I will explain the methodology.
DECLARE #Events TABLE (Event varchar(20), EventStart Time, EventEnd Time, Days varchar(50), Rooms varchar(10), DayStarts date)
INSERT INTO #Events
SELECT 'CISC 3660', '09:00:00', '12:30:00', 'Monday', '7-3', '9/19/2014' UNION
SELECT 'MATH 2501', '15:00:00', '17:00:00', 'Monday:Wednesday', '7-2', '10/13/2014' UNION
SELECT 'CISC 1110', '14:00:00', '16:00:00', 'Monday', '7-3', '9/19/2014'
DECLARE #Rooms TABLE (RoomName varchar(10))
INSERT INTO #Rooms
SELECT '7-2' UNION
SELECT '7-3'
DECLARE #SelectedDate date = '9/19/2014'
DECLARE #MinTimeInterval int = 30 --smallest time unit room can be reserved for
;WITH
D1(N) AS (
SELECT 1 UNION ALL SELECT 1 UNION ALL SELECT 1 UNION ALL
SELECT 1 UNION ALL SELECT 1 UNION ALL SELECT 1 UNION ALL
SELECT 1 UNION ALL SELECT 1 UNION ALL SELECT 1 UNION ALL SELECT 1
),
D2(N) AS (SELECT 1 FROM D1 a, D1 b),
D4(N) AS (SELECT 1 FROM D2 a, D2 b),
Numbers AS (SELECT TOP 3600 ROW_NUMBER() OVER (ORDER BY (SELECT NULL)) -1 AS Number FROM D4),
AllTimes AS
(SELECT CAST(DATEADD(n,Numbers.Number*#MinTimeInterval,'09:00:00') as time) AS m FROM Numbers
WHERE DATEADD(n,Numbers.Number*#MinTimeInterval,'09:00:00') <= '22:00:00'),
OccupiedTimes AS (
SELECT e.Rooms, ValidTimes.m
FROM #Events E
CROSS APPLY (SELECT m FROM AllTimes WHERE m BETWEEN CASE WHEN e.EventStart = '09:00:00' THEN e.EventStart ELSE DATEADD(n,1,e.EventStart) END and CASE WHEN e.EventEnd = '22:00:00' THEN e.EventEnd ELSE DATEADD(n,-1,e.EventEnd) END) ValidTimes
WHERE e.DayStarts = #SelectedDate
),
AllRoomsAllTimes AS (
SELECT * FROM #Rooms R CROSS JOIN AllTimes
), AllOpenTimes AS (
SELECT a.*, ROW_NUMBER() OVER( PARTITION BY (a.RoomName) ORDER BY a.m) AS pos
FROM AllRoomsAllTimes A
LEFT OUTER JOIN OccupiedTimes o ON a.RoomName = o.Rooms AND a.m = o.m
WHERE o.m IS NULL
), Finalize AS (
SELECT a1.RoomName,
CASE WHEN a3.m IS NULL OR DATEDIFF(n,a3.m, a1.m) > #MinTimeInterval THEN a1.m else NULL END AS FreeTimeStart,
CASE WHEN a2.m IS NULL OR DATEDIFF(n,a1.m,a2.m) > #MinTimeInterval THEN A1.m ELSE NULL END AS FreeTimeEnd,
ROW_NUMBER() OVER( ORDER BY a1.RoomName ) AS Pos
FROM AllOpenTimes A1
LEFT OUTER JOIN AllOpenTimes A2 ON a1.RoomName = a2.RoomName and a1.pos = a2.pos-1
LEFT OUTER JOIN AllOpenTimes A3 ON a1.RoomName = a3.RoomName and a1.pos = a3.pos+1
WHERE A2.m IS NULL OR DATEDIFF(n,a1.m,a2.m) > #MinTimeInterval
OR
A3.m IS NULL OR DATEDIFF(n,a3.m, a1.m) > #MinTimeInterval
)
SELECT F1.RoomName, f1.FreeTimeStart, f2.FreeTimeEnd FROM Finalize F1
LEFT OUTER JOIN Finalize F2 ON F1.Pos = F2.pos-1 AND f1.RoomName = f2.RoomName
WHERE f1.pos % 2 = 1
In the first several lines, I create temp variables to simulate your tables Events and Rooms.
The variable #MinTimeInterval determines what time interval the room schedules can be on (every 30 min, 15 min, etc - this number needs to divide evenly into 60).
Since SQL cannot query data that is missing, we need to create a table that holds all of the times that we want to check for. The first several lines in the WITH create a table called AllTimes which are all the possible time intervals in your day.
Next, we get a list of all of the times that are occupied (OccupiedTimes), and then LEFT OUTER JOIN this table to the AllTimes table which gives us all the available times. Since we only want the start and end of each free time, create the Finalize table which self joins each record to the previous and next record in the table. If the times in these rows are greater than #MinTimeInterval, then we know it is either a start or end of a free time.
Finally we self join this last table to put the start and end times in the same row and only look at every other row.
This will need to be adjusted if a single row in Events spans multiple days or multiple rooms.

Answer 2

Here's a solution that will return the "complete picture" including rooms that aren't booked at all for the day in question:
Declare #Date char(8) = '20141013'
;
WITH cte as
(
SELECT *
FROM -- use your table name instead of the VALUES construct
(VALUES
('09:00:00','12:30:00' ,'7-3', '20140919'),
('15:00:00','17:00:00' ,'7-2', '20141013'),
('14:00:00','16:00:00' ,'7-3', '20140919')) x(EventStart , EventEnd,Rooms, DayStarts)
), cte_Days_Rooms AS
-- get a cartesian product for the day specified and all rooms as well as the start and end time to compare against
(
SELECT y.EventStart,y.EventEnd, x.rooms,a.DayStarts FROM
(SELECT #Date DayStarts) a
CROSS JOIN
(SELECT DISTINCT Rooms FROM cte)x
CROSS JOIN
(SELECT '09:00:00' EventStart,'09:00:00' EventEnd UNION ALL
SELECT '22:00:00' EventStart,'22:00:00' EventEnd) y
), cte_1 AS
-- Merge the original data an the "base data"
(
SELECT * FROM cte WHERE DayStarts=#Date
UNION ALL
SELECT * FROM cte_Days_Rooms
), cte_2 as
-- use the ROW_NUMBER() approach to sort the data
(
SELECT *, ROW_NUMBER() OVER(PARTITION BY DayStarts, Rooms ORDER BY EventStart) as pos
FROM cte_1
)
-- final query: self join with an offest of one row, eliminating duplicate rows if a room is booked starting 9:00 or ending 22:00
SELECT c2a.DayStarts, c2a.Rooms , c2a.EventEnd, c2b.EventStart
FROM cte_2 c2a
INNER JOIN cte_2 c2b on c2a.DayStarts = c2b.DayStarts AND c2a.Rooms =c2b.Rooms AND c2a.pos = c2b.pos -1
WHERE c2a.EventEnd <> c2b.EventStart
ORDER BY c2a.DayStarts, c2a.Rooms