GPO (11/1/2010)
If it was your job to design these tables, would you be tempted to have an end_date_time column that could not be null, and instead substitute a ridiculous future date for all events that have not yet ended (like 22000101)? Are there indexing or other performance advantages to making your end_date_time column not null?
I would not be the least bit tempted to do that. Fake data is the bane of my existence.