I was about to prepare the query without ties and yes it is a lot harder than necessary and, more important IMO, much less readable/intuitive for people than have to maintain the code and that is exactly why different SQL dialects introduced ORDER BY/LIMIT/OFFSET/TOP/RANK etc.

But let me be a little bit picky about this and Date's view on ORDER BY.

The relational model deals just with the algebra/calculus without getting into the details of a language based on the model.

In the book pointed out by Matt, Date explicitly states he's not saying ORDER BY is not useful, just that it doesn't return a relation and thus it's not included in the algebra.

However a language based on the relational model, like Tutorial D, can include such an operator. To be double sure, I checked on The Third Manifesto V2 and a LOAD operator with an ORDER specification is defined in the context of the "special cased" support for arrays.

You can see a couple of paragraphs if you go here http://books.google.it/books?id=X85QAAAAMAAJ&dq=editions... and search for ORDER and LOAD (page 118).

TBH I'm not even sure it's a good idea to introduce arrays for ordering, but, anyway, back to the quota queries: we agree that regular aggregation operators are enough although the query becomes very complex.

In the same book referenced by Matt there's an exercise (7.14) showing how to do a quota query and you can see that even in Tutorial D it's complex.

However, in the solution, Date & Darwen also propose something else: to add a more specific RANK operator which is really just syntactic sugar to simplify this kind of queries. With the important difference, compared to ORDER, that it still returns a relation and not an ordered sequence of tuples.

Unfortunately the whole solution to the excercise is not available through Google Books preview, and the operator is formally defined elsewhere, but you can see how such RANK operator would work here http://books.google.it/books?id=WuZGD5tBfMwC&lpg=PA163&#...

Just a final comment about Date being reluctant to analyze the matter, unfortunately his work is disseminated in a lot of books (and he changed his position on quite several matters throughout the years).

I love the "SQL and Relational Theory" one but, having red all of his books, I would be hesitant to suggest it unless one already knows Date. I think the latest edition (8th) of "An Introduction to Database Systems" is still the best book to start with.