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Message Posted: Thu, 03 Jun 2004 @ 07:51:55 GMT

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Subj:   Re: Exclusion Joins
From:   Victor Sokovin


  For close to 20 years I have been telling Teradata technicians to avoid using nulls in their databases. There is a place for nulls, but not what I find in customer developed applications.  

It might be difficult at times but it should be possible to build a database without NULLs in the tables. However, NULLs will soon appear in intermediate data sets in SQL queries. For example, in outer joins. I think NULL is a mathematical necessity required by the algebraic model used in relational databases. We might try to give them different names but at the end of the day there will emerge something which mathematicians might call an isomorphic algebra. Until some significant progress is made in the current algebraic model there will be no progress in the isomorphic one. I am not aware of any alternative working algebraic model which would deliver consistently better results.

It would be difficult to get rid of such constructs as outer joins. Many users like to use them because they have to work with different RDBMS, and on some platforms outer joins are rather efficient.

Just a few thoughts on the topic. It would be interesting to hear your comments on them.



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