Re: NULL

From: --CELKO-- <jcelko212_at_earthlink.net>
Date: 1 Oct 2004 06:35:50 -0700
Message-ID: <18c7b3c2.0410010535.ab37196_at_posting.google.com>


>> If somebody could shed some light on the early history of NULL in
databases, I would be grateful. Pure curiosity. <<

I think they first came out of System R at IBM because Dr. Codd had them in his papers. The theory says they have no data type and have no value; the implementations have to reserve storage, so you have things like "CAST (NULL AS <datatype>)" in SQL.

Before that, Statistic packages had ways of handling missing data -- I think SPSS was the first one. But they were often resolved a fictional value for computations.

I would have to look this up, but I recall that SPARC had a paper in the 1970's on over a dozen diffrent kinds of missing data -- overflow, underflow, divide by zero, illegal bit patterns, unknown, missing, N/A, impossible value, etc. And of course IEEE floating point has "Nan" which is like a missing value marker.

In spite of what Fabian Pascal says, applied math spends a lot of time on "things we don't know" ... Received on Fri Oct 01 2004 - 15:35:50 CEST

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