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Re: Eliminating Nulls

From: -CELKO- <jcelko212_at_earthlink.net>
Date: 1 Jul 2005 08:25:57 -0700
Message-ID: <1120231557.523100.275230@g49g2000cwa.googlegroups.com>


NULLs are not automatically bad. The real questions are:

  1. Does this attribute belong with this entity? if yes, then do not split it out.
  2. 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
  3. Does it make sense to drop NULLs form aggregations for this attribute?
  4. 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

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