Opening Hours Database Design

Question

We are currently developing an application in which multiple entities have associated opening hours. Opening hours may span multiple days, or may be contained within a single day.

Ex. Opens Monday at 6:00 and closes at Friday at 18:00.

Or

Opens Monday at 06:00 and closes Monday at 15:00.

Also, an entity may have multiple sets of opening hours per day. So far, the best design I have found, is to define an opening hour to consist of the following:

StartDay, StartTime, EndDay and EndTime.

This design allows for all the needed flexibility. However, data integrity becomes an issue. I cannot seem to find a solution that will disallow overlapping spans (in the database).

Please share your thoughts.

EDIT: The database is Microsoft SQL Server 2008 R2

Answer 1

Presuming a robust trigger framework

On insert/update you would check if the new start or end date falls inside of any existing range. If it does then you would roll back the change.

CREATE TRIGGER [dbo].[mytable_iutrig] on [mytable] FOR INSERT, UPDATE AS

IF (SELECT COUNT(*)
FROM inserted, mytable
WHERE (inserted.startdate < mytable.enddate 
          AND inserted.startdate > mytable.startdate)
      OR (inserted.enddate < mytable.enddate 
          AND inserted.enddate > mytable.startdate)) > 0 
BEGIN
    RAISERROR --error number
    ROLLBACK TRANSACTION
END

Answer 2

Consider storing your StartDay and StartTime, but then have a value for the number of hours that it's open. This will ensure that your closing datetime is after the opening.

OpenDate -- day of week? e.g. 1 for Monday
OpenTime -- time of day. e.g. 08:00
DurationInHours -- in hours or mins. e.g.   15.5

Answer 3

There's an article by Joe Celko on the SimpleTalk website, over here, that discusses a similar issue, and presents am elegant if complex solution. This is probably applicable to your situation.

Answer 4

A table with a single column TimeOfChangeBetweenOpeningAndClosing?

More seriously though, I would probably not worry too much about coming up with a single database structure for representing everything, eventually you'll probably want want a system involving recurrences, planned closures etc. Persist objects representing those, and then evaluate them to find out the closing/opening times.

Answer 5

Detecting and preventing overlapping time periods will have to be done at the application level. Of course you can attempt to use a trigger in the database but in my opinion this is not a database issue. The structure that you came up with is fine, but your application logic will have to take care of the overlap.

Answer 6

This looks like a good solution, but you'll have to write a custom validation function. The built in database validation (i.e. unique, less than x, etc.) isn't going to cut it here. To ensure you don't have overlapping spans, every time you insert a record into the database, you're going to have to select existing records and compare...

Answer 7

First the logic, two spans will overlap if the start value of one falls between the start/end of the other. This is much easier if we have datetimes combined, instead of date1,time1 and date2,time2. So a query to find an overlap looks like this.

select openingId
  from opening o1
  join opening o2 on o1.startDateTime 
             between o2.startDateTime
                 AND o2.endDateTime

You can put this into a trigger and throw an error if a match is found.