Checking a range of dates in SQL - sql-server

Question

Following on from a question I put on yesterday, I need to return a range of "available" dates for a laptop rollout "booking system". I want to populate a table of possible available dates a user can book a slot on by checking for each date the total possible number of slots, and subtracting the number of slots already booked.
The logic is as follows:
A technician can build 3 laptops per day.
On any day there may be 1, 2 or 3 technicians available.
A table holds the bookings made
I don't want a table of all possible dates, I want to calculate it on the fly
Relevant tables are:
tl_sb_slotBooking
This contains the bookings already made
tl_sb_availabilityPeriods
This is used to calculate the total number of available slots on a given day
I can bring back a list of dates with a fixed maximum number (in this case 3) of slots:
DECLARE #startDate DATE
DECLARE #endDate DATE
SET #startDate = GETDATE()
SET #endDate = DATEADD(m,3,#startDate)
;
WITH dates(Date) AS
(
SELECT #startdate as Date
UNION ALL
SELECT DATEADD(d,1,[Date])
FROM dates
WHERE DATE < #enddate
)
SELECT Date
FROM dates
EXCEPT
SELECT date
FROM tl_sb_booking
GROUP BY date
HAVING COUNT(date) >= 3
However, the maximum won't always be 3, it changes for each day.
I can find the maximum possible slots for a given day:
DECLARE #myDate DATETIME = '2013-06-22'
SELECT SUM(laptopsPerDay) AS totalSlots
FROM tl_sb_technicianAvailability
WHERE startDate <= #myDate AND endDate >= #myDate
AND availabiltyStateID=3
it will bring back 6 as the total number of slots available for 2013-06-22. (The availabilityStateID field is used to store available/unavailable etc.)
So, the bit I am stuck on is combining the two.
What I want is for each possible date, if the number of slots already booked is less than the number of possible slots for that day, add it to the table being returned (otherwise don't).

Answer 1

Firstly, althought you are only generating a small list, using a CTE to generate a sequential list performs terribly and is best avoided.
For the sake of this I will use the system table Master..spt_values for a sequential list of numbers, but if you are worried about using undocumented system tables then there are other methods in the link above.
The first thing I would do is split the technician availability dates into a row per day, this will allow for technicians who are available for only part of the peiod required (e.g. from your sceen shot of the table if you wanted to query from 18th June to 26th June none of the technicians show would appear as available using the query you have posted):
SELECT Date = DATEADD(DAY, spt.Number, ta.StartDate),
ta.TechnicianID,
ta.LapTopsPerDay
FROM tl_sb_technicianAvailability ta
INNER JOIN Master..spt_values spt
ON spt.Type = 'P'
AND spt.Number BETWEEN 0 AND DATEDIFF(DAY, ta.startDate, ta.EndDate)
This would simply turn:
TechnicianID StartDate EndDate LapTopsPerDay
1 20130620 20130624 3
into
Date TechnicianID LapTopsPerDay
20130620 1 3
20130621 1 3
20130622 1 3
20130623 1 3
20130624 1 3
You can then limit this list to the date range required, and sum up the total laptops than can be done as this is not needed on a technicial level:
WITH ExplodedAvailability AS
( SELECT Date = DATEADD(DAY, spt.Number, ta.StartDate),
ta.TechnicianID,
ta.LapTopsPerDay
FROM tl_sb_technicianAvailability ta
INNER JOIN Master..spt_values spt
ON spt.Type = 'P'
AND spt.Number BETWEEN 0 AND DATEDIFF(DAY, ta.startDate, ta.EndDate)
)
SELECT Date, TotalLaptops = SUM(LapTopsPerDay)
FROM ExplodedAvailability
WHERE Date >= #StartDate
AND Date < #EndDate
GROUP BY Date;
Finally you can LEFT JOIN to the bookings table to get the available slots per day
WITH ExplodedAvailability AS
( SELECT Date = DATEADD(DAY, spt.Number, ta.StartDate),
ta.TechnicianID,
ta.LapTopsPerDay
FROM tl_sb_technicianAvailability ta
INNER JOIN Master..spt_values spt
ON spt.Type = 'P'
AND spt.Number BETWEEN 0 AND DATEDIFF(DAY, ta.startDate, ta.EndDate)
), Availability AS
( SELECT Date, TotalLaptops = SUM(LapTopsPerDay)
FROM ExplodedAvailability
WHERE Date >= #StartDate
AND Date < #EndDate
GROUP BY Date
), Bookings AS
( SELECT Date, SlotsBooked = COUNT(*)
FROM tl_sb_booking
GROUP BY Date
)
SELECT Availability.Date,
Availability.TotalLaptops,
RemainingSlots = Availability.TotalLaptops - ISNULL(Bookings.SlotsBooked, 0)
FROM Availability
LEFT JOIN Bookings
ON Bookings.Date = Availability.Date;
I think what you are after is to add a booking to the next available day, so the query to do this would be:
DECLARE #UserID INT = 1;
WITH ExplodedAvailability AS
( SELECT Date = DATEADD(DAY, spt.Number, ta.StartDate),
ta.TechnicianID,
ta.LapTopsPerDay
FROM tl_sb_technicianAvailability ta
INNER JOIN Master..spt_values spt
ON spt.Type = 'P'
AND spt.Number BETWEEN 0 AND DATEDIFF(DAY, ta.startDate, ta.EndDate)
), Availability AS
( SELECT Date, TotalLaptops = SUM(LapTopsPerDay)
FROM ExplodedAvailability
WHERE Date >= CAST(GETDATE() AS DATE)
GROUP BY Date
), Bookings AS
( SELECT Date, SlotsBooked = COUNT(*)
FROM tl_sb_booking
GROUP BY Date
)
INSERT tl_sb_slotBooking (UserID, Date)
SELECT #UserID, MIN(Availability.Date)
FROM Availability
LEFT JOIN Bookings
ON Bookings.Date = Availability.Date
WHERE Availability.TotalLaptops > ISNULL(Bookings.SlotsBooked, 0)

Answer 2

Should this be of use to anyone, this is the way I ultimately did it:
DECLARE #startDate DATE
DECLARE #endDate DATE
SET #startDate = GETDATE()
SET #endDate = DATEADD(m,3,#startDate)
;
WITH dates(currentDate) AS
(
SELECT #startdate as currentDate
UNION ALL
SELECT DATEADD(d,1,[currentDate])
FROM dates
WHERE currentDate < #enddate
)
SELECT currentDate
FROM dates
WHERE /* slots booked for date */
(
SELECT count([date])
FROM tl_sb_booking
where [date] = currentDate
)
<
/* total slots available */
(
SELECT SUM(laptopsPerDay) AS totalSlots
FROM tl_sb_technicianAvailability
WHERE startDate <= currentDate AND endDate >= currentDate
AND availabiltyStateID=3
)