Re: Character string relation and functional dependencies

From: Jonathan Leffler <jleffler_at_earthlink.net>
Date: Thu, 06 Dec 2007 14:38:48 -0800
Message-ID: <13lgug1pkaflra6@corp.supernews.com>

Tegiri Nenashi wrote:
> On Dec 6, 9:40 am, rp..._at_pcwin518.campus.tue.nl (rpost) wrote:

>> Another difference is that database tables are finite and variable,

>
> Oh, relations in database world are certainly not restricted by finite
> cardinality.

I thought that computers are finite, so the relations containable in them are too - even if damn large. There's a big difference between very large and infinite.

One ultimate limitation is the uniqueness requirement. Suppose you have a table with two integer columns. Since the range of the integer types are finite (even if your DBMS handles multi-precision integers), then the maximum number of distinct rows in the relation is also finite.

-- 
Jonathan Leffler                   #include <disclaimer.h>
Email: jleffler_at_earthlink.net, jleffler_at_us.ibm.com
Guardian of DBD::Informix v2007.0914 -- http://dbi.perl.org/

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Received on Thu Dec 06 2007 - 16:38:48 CST