>>"Magic numbers" are poison. I don't want them anywhere near my code.

If by "magic number" you mean 12/30/1899, I agree with you and Janis that it's better to use some other placeholder to denote absence of value rather than SQL Server's interpretation of a blank date.

The other significant databases (Oracle, MySQL and SQLite) even treat NULL as distinct in a Unique column so it can still be used: SQL Server does not allow this. If there are indeed large databases out there with no NULLs, perhaps being in the MS camp has something to do with it.

FWIW: to my astonishment I recently met a man who had inherited a coin collection comprising old roman coins with a particular interest in gold coins minted by or for Roman Emperors. He had tray after tray of coins with occasional gaps where coins were yet to be located for an emperor or two. Suffice to say that the date on all those coins was well before 1753 and there was a whole tray full of query coins requiring further investigation. 15 years ago it would have been easier to create a database app for those coins using contemporary MS technology than it is today.