So is this what is needed?
ALTER TABLE dbo.Test ADD CONSTRAINT CK_Test_EndDateAfterStartDateAndNotNull CHECK (EndDate > StartDate AND EndDate IS NOT NULL);
GO
well, I could also do this:
CREATE TABLE dbo.Test
(
ID INT NOT NULL,
StartDate DATETIME NOT NULL,
EndDate DATETIME not NULL
);
GO
ALTER TABLE dbo.Test ADD CONSTRAINT CK_Test_EndDateAfterStartDate CHECK (EndDate > StartDate);
GO
I normally default Enddate to "9999-12-31", and do not allow Unknown dates.