Re: Extending my question. Was: The relational model and relationalalgebra - why did SQL become the industry standard?

From: Lauri Pietarinen <>
Date: Thu, 13 Feb 2003 15:32:09 +0200
Message-ID: <>

>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.

I agree that ordering is needed to present data and that a "set" such ordered rows are not
relations anymore.

>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.

However, you would include the line number column to get the rows in the correct order. You would just disregard the column in your program or report generator.

So the end result of the query would _not_ have duplicates!

Lauri Pietarinen Received on Thu Feb 13 2003 - 14:32:09 CET

Original text of this message