Re: Extending my question. Was: The relational model and relationalalgebra - why did SQL become the industry standard?
Date: Thu, 13 Feb 2003 13:36:20 +0100
Lauri Pietarinen wrote:
> I don't think that anybody is suggesting that intermediate results need
> to remove duplicates. It's
> the end result that counts. E.g. in the following code fragment
Well, I think that even for end results duplicates can be useful. It is the difference between the set theory and query results in practice. For instance: a set doesn't have an order but it would be impossible to present results to a user of our database if we cannot order the end result.
To give an example of the use of duplicates: Suupose we have a table that holds text (letters for instance). We would probably have a line number field and a text field. To improve readability we will have several occurrences of blank lines. If we then select the text column ordered by the line number, we will have (meaningful) duplicates in the end result.
> Lauri Pietarinen, Senior Consultant, Databases
> AtBusiness Communications Oyj, Kaapeliaukio 1, FIN-00180 Helsinki
> tel. +358-9-2311 6632, mob. +358-50-594 2011, fax +358-9-2311 6601
> http://www.atbusiness.com, email: lauri.pietarinen_at_atbusiness.com
-- Anton Versteeg DB2 Specialist IBM NetherlandsReceived on Thu Feb 13 2003 - 13:36:20 CET