Finding free slots in a booking system

Question

In my question about searching for date ranges I tried simplifying the problem and inadvertently posed a different and simpler problem.

Rather than complicate that q

Answer 1

Table definitions would have helped, but here goes. This should work for MS SQL Server, but it should be a trivial task to convert it to MySQL once you understand the idea behind it.

The Calendar table is just a standard utility table with all of the dates in it that is useful to have in your database. If you don't already have one, I suggest that you create one and populate it.

CREATE TABLE Calendar
(
     date        DATETIME     NOT NULL,
     is_holiday  BIT          NOT NULL,
     -- any other columns that might be relevant for your business
     CONSTRAINT PK_Calendar PRIMARY KEY CLUSTERED (date)
)

You would then need to populate the table with any dates that might be meaningful for your business. Even if you go back 100 years and forward 100 years, that's still less than 75K rows in the table and it's clustered on the date, so it should be fast and easy to work with. It makes many date-based queries much simpler.

SELECT
     P.property_id,
     C.date
FROM
     Calendar C
JOIN Properties P ON 1=1
WHERE
     C.date BETWEEN @search_start_date AND @search_end_date AND
     NOT EXISTS
     (
          SELECT
               *
          FROM
               Bookings B
          WHERE
               B.property_id = P.property_id AND
               B.start_date <= DATEADD(dy, @slot_length, C.date) AND  -- You would use MySQLs date function
               B.end_date   >= C.date
     )

Or alternatively:

SELECT
     P.property_id,
     C.date
FROM
     Calendar C
JOIN Properties P ON 1=1
LEFT OUTER JOIN Bookings B ON
               B.property_id = P.property_id AND
               B.start_date <= DATEADD(dy, @slot_length, C.date) AND  -- You would use MySQLs date function
               B.end_date   >= C.date
WHERE
     C.date BETWEEN @search_start_date AND @search_end_date AND
     B.booking_id IS NULL