Selecting time windows based on availability in SQL

Question

I have a data set with several time windows, an availability indicator and a priority index.

Create data set:

CREATE TABLE TimeWindows(
TimeFrom DATETIME NOT NULL,
TimeTo DATETIME NOT NULL,
Priority INT NOT NULL,
Available BIT NOT NULL
);

INSERT INTO TimeWindows(TimeFrom, TimeTo, Priority, Available) VALUES
('2017-07-22 07:00:00', '2017-07-22 12:00:00', 1, 1),
('2017-07-22 13:00:00', '2017-07-22 17:00:00', 1, 1),
('2017-07-22 12:30:00', '2017-07-23 00:00:00', 3, 0),
('2017-07-23 07:00:00', '2017-07-23 12:00:00', 1, 1),
('2017-07-23 13:00:00', '2017-07-23 17:00:00', 1, 1),
('2017-07-23 00:00:00', '2017-07-24 00:00:00', 2, 0),
('2017-07-23 19:00:00', '2017-07-23 20:00:00', 4, 1),
('2017-07-24 07:00:00', '2017-07-24 12:00:00', 1, 1),
('2017-07-24 13:00:00', '2017-07-24 17:00:00', 1, 1),
('2017-07-24 15:00:00', '2017-07-24 16:00:00', 4, 0);

Example data set:

| TimeFrom            | TimeTo              | Priority | Available |
|---------------------|---------------------|----------|-----------|
| 2017-07-22 07:00:00 | 2017-07-22 12:00:00 |        1 |         1 |
| 2017-07-22 13:00:00 | 2017-07-22 17:00:00 |        1 |         1 |
| 2017-07-22 12:30:00 | 2017-07-23 00:00:00 |        3 |         0 |
| 2017-07-23 07:00:00 | 2017-07-23 12:00:00 |        1 |         1 |
| 2017-07-23 13:00:00 | 2017-07-23 17:00:00 |        1 |         1 |
| 2017-07-23 00:00:00 | 2017-07-24 00:00:00 |        2 |         0 |
| 2017-07-23 19:00:00 | 2017-07-24 20:00:00 |        4 |         1 |
| 2017-07-24 07:00:00 | 2017-07-24 12:00:00 |        1 |         1 |
| 2017-07-24 13:00:00 | 2017-07-24 17:00:00 |        1 |         1 |
| 2017-07-24 15:00:00 | 2017-07-24 16:00:00 |        4 |         0 |

Problem:

I want to generate a new set of time windows, which only represent the available time slots.

Business rules:

• Time windows with a higher priority, will overrule conflicting time windows with a lower priority
• Availability indicator is set to 1 if available and is set to 0 if not available
• Overlapping time windows need to be consolidated
• An available time window which is 'split' by a period of unavailability, will be converted into two separate available time windows

Desired results:

| TimeFrom            | TimeTo              |
|---------------------|---------------------|
| 2017-07-22 07:00:00 | 2017-07-22 12:00:00 |
| 2017-07-23 19:00:00 | 2017-07-23 20:00:00 |
| 2017-07-24 07:00:00 | 2017-07-24 12:00:00 |
| 2017-07-24 13:00:00 | 2017-07-24 15:00:00 |
| 2017-07-24 16:00:00 | 2017-07-24 17:00:00 |

Can anyone advise me on how to solve this problem in SQL?

Thanks in advance for your help.

Answer 1

Well, It's been a while since I've solved a good sql challenge, so I got the hard part for you done. Using a CTE with some case statements and another query with some more case statements to get all the bussiness rules but one -

Overlapping time windows need to be consolidated.

but that's really the easy part. You'll see a lot of comments in the code that explains the logic, and of course, I could only test myself against your sample data, but it should get you started.

There might be other, better solutions for this, but this is what I came up with:

;WITH CTE AS
(

SELECT  t0.TimeFrom As AvailableFrom,
        t0.TimeTo As AvailableTo,
        t1.TimeFrom As UnavailableFrom,
        t1.TimeTo As UnavailableTo,
        CASE WHEN t1.Available IS NULL THEN 
            -- no overlapping records with higher priority and available = 0, use t0 start and end.
            1 -- t0.TimeFrom, t0.TimeTo
        ELSE
            CASE 
                WHEN t0.TimeFrom > t1.TimeFrom AND t0.TimeTo < t1.TimeTo THEN
                -- t0 is inside t1, record of t0 can't be used.
                0
                WHEN t0.TimeFrom < t1.TimeFrom AND t0.TimeTo < t1.TimeTo THEN
                -- t0 starts before t1 starts, and also ends before t1 ends. this means that the start will be t0 start.
                2 -- t0.TimeFrom, t1.TimeFrom
                WHEN t0.TimeFrom > t1.TimeFrom AND t0.TimeTo > t1.TimeTo THEN
                -- t0 starts after t1, but also ends after it. this means that the start will be t1 end.
                3 -- t1.TimeTo, t0.TimeTo
                WHEN t0.TimeFrom < t1.TimeFrom AND t0.TimeTo > t1.TimeTo THEN
                -- t1 is inside t0, need to create 2 records for this.
                4 -- 2 records - t0.TimeFrom, t1.TimeFrom and also t1.TimeTo and t0.TimeTo
            END
        END As RecordType
FROM TimeWindows t0
LEFT JOIN TimeWindows t1 ON t0.TimeFrom <= t1.TimeTo -- t1 overlaps t0
                        AND t0.TimeTo >= t1.TimeFrom -- t1 overlaps t0
                        AND t0.Priority < t1.Priority -- t1 priority is higher than t0 priority
                        AND t1.Available = 0 -- t1 records are unavaialbe
WHERE t0.Available = 1 -- t0 records are available
-- t0 holds all the available time slots, 
-- while t1 holds all the unavailable time slots that overlap t0 records and have a higher priority. (otherwise they don't matter...)
)

SELECT  CASE RecordType
            WHEN 1 THEN
                AvailableFrom
            WHEN 2 THEN
                AvailableFrom
            WHEN 3 THEN
                UnavailableTo
            WHEN 4 THEN
            AvailableFrom
        END As TimeFrom,
        CASE RecordType
            WHEN 1 THEN
                AvailableTo
            WHEN 2 THEN
                UnavailableFrom
            WHEN 3 THEN
                AvailableTo
            WHEN 4 THEN
            UnavailableFrom
        END As TimeTo
FROM CTE 
WHERE RecordType > 0
UNION ALL
SELECT  UnavailableTo,
        AvailableTo
FROM CTE 
WHERE RecordType =4 

Results:

TimeFrom                TimeTo
22.07.2017 07:00:00     22.07.2017 12:00:00
23.07.2017 19:00:00     23.07.2017 20:00:00
24.07.2017 07:00:00     24.07.2017 12:00:00
24.07.2017 13:00:00     24.07.2017 15:00:00
24.07.2017 16:00:00     24.07.2017 17:00:00

You can see a live demo on rextester.