How do i find available date ranges from date ranges - sql

Question

Sql Server
I already added bookings from my hotel room management system reservation data. I want sql query for retrieve rooms available date ranges and also i want find specific date range is available

Answer 1

You can use something like the following. It's not an easy query, I'll try to explain as simple as possible.
Use a recursive CTE to generate dates from a specified start date to a specified end date.
Join each date to the different room IDs you might have in your table to create all potential available dates.
Determine which dates are unavailable for each room.
Determine which dates are available for each room by joining all potential available dates and removing unavailable ones (point 2 vs 3).
Determine how to group by each range (I used a ROW_NUMBER with a DENSE_RANK).
Display results in intervals, for each room.
Script:
-- Period to consider
DECLARE #StartDate DATE = '2018-06-20'
DECLARE #EndDate DATE = '2018-09-01'
;WITH GeneratedDates AS
(
SELECT
GeneratedDate = #StartDate
UNION ALL
SELECT
GeneratedDate = DATEADD(DAY, 1, G.GeneratedDate)
FROM
GeneratedDates AS G
WHERE
G.GeneratedDate < #EndDate
),
ExistingRooms AS
(
SELECT DISTINCT
RoomId
FROM
HotelReservation.dbo.Reservation AS R
),
UnavailableDatesByRoom AS
(
SELECT DISTINCT
R.RoomID,
UnavailableDate = G.GeneratedDate
FROM
HotelReservation.dbo.Reservation AS R
INNER JOIN GeneratedDates AS G ON G.GeneratedDate BETWEEN R.CheckIn AND R.CheckOut
),
AvailableDaysByRoom AS
(
SELECT
AvailableDate = G.GeneratedDate,
E.RoomID,
DateRanking = ROW_NUMBER() OVER (PARTITION BY E.RoomID ORDER BY G.GeneratedDate ASC)
FROM
GeneratedDates AS G
CROSS JOIN ExistingRooms AS E
WHERE
NOT EXISTS (
SELECT
'unavailable date for that room'
FROM
UnavailableDatesByRoom AS U
WHERE
U.RoomID = E.RoomID AND
G.GeneratedDate = U.UnavailableDate)
),
AvailableDaysByRoomGroupings AS
(
SELECT
A.*,
MagicRanking = DENSE_RANK() OVER (PARTITION BY A.RoomID ORDER BY DateRanking - DATEDIFF(DAY, '2010-01-01', A.AvailableDate))
FROM
AvailableDaysByRoom AS A
)
SELECT
G.RoomID,
FirstAvailableStartDate = MIN(G.AvailableDate),
LastAvailableStartDate = MAX(G.AvailableDate)
FROM
AvailableDaysByRoomGroupings AS G
GROUP BY
G.RoomID,
G.MagicRanking
ORDER BY
G.RoomID,
FirstAvailableStartDate
OPTION
(MAXRECURSION 32000)