check conflict between two datetimepicker

Question

So I'm making a simple reservation system ,C# and sql . I have datetimepicker 1 and datetimepicker 2 . For ex. datetimepicker = aug 1 2009 and datetimepicker2 = aug 3 2009 saved in sql by the user .

What to do with that so that the next customer that would try to get the date 1-3 would be forced to choose another date ?

Answer 1

You can run a query like this one:

select count(*) as cnt
from reservations t
where
not 
(

    (@dtTo <= t.DateFrom)

    or

    (@dtFrom >= t.DateTo)

)

assuming that @dtFrom, @dtTo are the dates the second user has chosen, and assuming
you have a reservations table with DateFrom and DateTo columns.

• If this query returns 0, then allow the second user to save.
• If it returns a number > 0, then don't allow the second user to save.

What's the idea behind this:
two segments of time [dateFrom1, dateTo1] and [dateFrom2, dateTo2] are not
conflicting (ie are not overlapping) for this reservation-based scenario if and only if:
dateTo1 <= dateFrom2 or dateFrom1 >= dateTo2
(draw it on a piece of paper and you'll see why).
So if the negation
not ( dateTo1 <= dateFrom2 or dateFrom1 >= dateTo2 )
is true, the two segments are overlapping/conflicting.