I am back and have been taking a set of new questions on asktom. Last week was a busy one out in California and I'm finally getting caught up on emails and questions (100% on the former, still working on the latter)
Anyway, I saw an article and it made me laugh - and sort of cry at the same time. It has to do with the use of default values. A lot of developers/DBAs have a very certain fear (that is the best word I can think of to describe their attitude) of NULL - the 'unknown' value. So, instead of using NULL for an effective_end_date field (for records that we don't know the end date for, they don't have one) or using NULL for values they do not know the value of - they use some 'fake' value. This fake value is assumed to be a value that could never possibly be used.
Things change over time.
I'm sure when the developers implemented this system - using XXXXXXX for a license plate value that was unknown seemed 'reasonable'. I mean - who would ever ask for a vanity plate with seven X's on them?
Talk to the guy with almost $20k in fines that aren't his to see if he might know someone that might want a vanity plate with XXXXXXX on it :)
Do not fear NULL.
Understand it, but don't fear it.