NULLs are not automatically bad. The real questions are:
- Does this attribute belong with this entity? if yes, then do not
split it out.
- Does this attribute have one or more unknown reasons for a missing
value? If yes, then encode them. Example: in ICD (International
Classification of Disease) 000.000 means 'undiagnosed' while 999.999'
means 'diagnosed, but unknown disease' -- two very different kidns of
missing values
- Does it make sense to drop NULLs form aggregations for this
attribute?
- Is there a natural default value? For numerics this is often zero.
For strings, like your example, it is often a note like '{{ to be
determined }}' -- I like curvy brackets to force them to sort to the
end of a listing and be easy to search.
Received on Fri Jul 01 2005 - 10:25:57 CDT
