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

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

1. 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):

  http://citeseer.nj.nec.com/407307.html

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