SQL DateTime比较

Question

I have a calender where a user can create appointments, I don't want double bookings nor do i want bookings overlapping one another.

I think to achieve this the following logic would do the trick.

Do not Allow bookings when:

@StartDateRequested <= Appointments.StartDate AND EndDateRequested >= Appointments.EndDate @StartDateRequested >= Appointments.StartDate AND EndDateRequested <= Appointments.EndDate

This Should stop bookings that are within a another bookings start and end, and stop bookings that start before and end after.

This is what i have tried:

DECLARE @ScheduledStart datetime2
SET @ScheduledStart = '2014/07/21 11:00:00 PM'

DECLARE @ScheduledEnd datetime2
SET @ScheduledEnd = '2014/07/21 13:55:00 PM'

DECLARE
    @ErrorMessage varchar(128)
    ,@IsLocalTrans bit

DECLARE @Count int

SELECT
    --@Count = COUNT(*)
    A.AppointmentId
FROM
    Appointment AS A WITH (NOLOCK)
WHERE
    (
    --  (@ScheduledStart BETWEEN A.ScheduledStart AND A.ScheduledEnd)
    --OR
    --  (@ScheduledEnd BETWEEN A.ScheduledStart AND A.ScheduledEnd)
    --OR
        (@ScheduledStart < A.ScheduledStart AND @ScheduledEnd > A.ScheduledEnd)
    OR
        (@ScheduledStart > A.ScheduledStart AND @ScheduledEnd < A.ScheduledEnd)
    )
    AND A.AppointmentStatusId = 2 --confirmed

This has failed it returned 3 appointments which start and end time were both greater then the start and end times of the dates i tried.

The commented out code, worked for stopping a booking if it started or ended in another bookings slot, but did not cater for bookings that overlap.

I think i'm on the right track, just my sql datetime logic is off.

In my database i have an appointment that starts at 12:00 to 12:55, You will see in my testing values i'm trying to check if i can create an appointment for 11:00 to 13:55, This should not allow me to do this.

Answer 1

This logic for overlaps of time is that there is an overlap when one starts before the other ends and the other ends after the first starts. The following logic returns overlaps:

WHERE (@ScheduledStart <= A.ScheduledEnd AND
       @ScheduledEnd >= A.ScheduledStart
      )

The following returns non-overlaps:

WHERE (@ScheduledStart > A.ScheduledEnd OR
       @ScheduledEnd < A.ScheduledStart
      )

Answer 2

The Logic i used in the end looked like this:

WHERE
(
    (@ScheduledStart BETWEEN A.ScheduledStart AND A.ScheduledEnd)
OR
    (@ScheduledEnd BETWEEN A.ScheduledStart AND A.ScheduledEnd)
OR
    (A.ScheduledStart BETWEEN @ScheduledStart AND @ScheduledEnd)
OR
    (A.ScheduledEnd BETWEEN @ScheduledStart AND @ScheduledEnd)
)