Re: Extending my question. Was: The relational model and relationalalgebra - why did SQL become the industry standard?
Date: 15 Feb 2003 10:13:53 +0100
Lauri Pietarinen wrote:
>I would be glad if somebody could tell me how counting
>and quota queries are expressed in "pure algebra" or
>do we need some extensions?
You need an extension. An important paper on that is
- Klug. Equivalence of Relational Algebra and Relational Calculus Query Languages Having Aggregate Functions. Journal of the ACM, 29(3):699--717, 1982.
Unfortunateley it is not on-line but a paper by Leonid Libkin (the guy is a phenomenon) on the expressive power of SQL also explains it (and a lot more):
Section 3 page 7, 8 and 9. Normally you could ask me if you have any questions about this paper, but I will be on a holiday in the next 7 days, so my response may be a little slow. :-)
- Jan Hidders