Stackoverflow - Selecting time windows based on availability in SQL, Sql Server

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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);

;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
                        AND t0.TimeTo >= t1.TimeFrom
                        AND t0.Priority < t1.Priority
                        AND t1.Available = 0
WHERE t0.Available = 1

)

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

/*
desired output
| 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 |
*/

View schema
Execution time: 0,03 sec, rows selected: 5, rows affected: 10, absolute service time: 0,17 sec