Question

I have a table that consists of, among other things, two fields named StartTime and EndTime. Both are TIME fields.

I want to add a constraint preventing the insertion of any records that overlap with preexisting time ranges. E.g. if a record already exists with StartTime = 5:00, EndTime = 10:00, I would want an insert with StartTime = 6:00, EndTime = 9:00 to fail due to the overlap.

Is there any way to accomplish this, with or without triggers?

Answer 1

The trigger below should work – it is also possible to do this with check contraints, but the logic shown in this post kind of hurts my head.

CREATE TRIGGER [dbo].[DateRangeTrigger]
   ON  [dbo].[TargetTable]
   FOR INSERT, UPDATE
AS 
BEGIN

IF EXISTS (SELECT t.starttime, t.endtime FROM TargetTable t
        Join inserted i
        On (i.starttime > t.starttime AND i.starttime < t.endtime AND i.UniqueId <> t.UniqueId) 
           OR (i.endtime < t.endtime AND i.endtime > t.starttime AND i.UniqueId <> t.UniqueId)
           OR (i.starttime < t.starttime AND i.endtime > t.endtime AND i.UniqueId <> t.UniqueId)
        )
BEGIN
    RAISERROR ('Inserted date was within invalid range', 16, 1)
    IF (@@TRANCOUNT>0)
        ROLLBACK
END


END