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Re: c.d.theory glossary - NULL

From: Laconic2 <laconic2_at_comcast.net>
Date: Tue, 27 Apr 2004 13:02:56 -0400
Message-ID: <JOOdnbC2EuGbDxPdRVn_iw@comcast.com>


> But those "nulls" are very different to the SQL nulls. SQL nulls are
> logical, not physical.

Your statement is implementation dependent.

InOracle, a zero byte in a VARCHAR field indicates a NULL. It also indicates a character string of length zero. That's why you can't tell them apart.

In DEC Rdb, every row is stored in a "record". (The user never sees this). At the end of every record is a bit vector marking "missing data". That's a physical structure. And it indicates precisely the same thing that the SQL NULL indicates. Received on Tue Apr 27 2004 - 12:02:56 CDT

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