Unique date range fields in SQL Server 2008

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 insertio

Answer 1

This trigger will also work for situations where one timespan completely contains the other. For example, if there's an existing record for 6:00 - 9:00 and you try to insert one for 5:00 - 10:00.
(Based on David Hall's answer)

CREATE TRIGGER DateRangeOverlapTrigger
ON  TargetTable
FOR INSERT, UPDATE
AS 
BEGIN
IF EXISTS
    (SELECT t.UniqueId
    FROM TargetTable t
        JOIN inserted i ON i.starttime < t.endtime
            AND i.endtime > t.starttime
            AND i.UniqueId <> t.UniqueId)
BEGIN
    RAISERROR ('Invalid due to time overlap', 16, 1)
    IF (@@TRANCOUNT > 0)
        ROLLBACK
END
END