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

Lauri Pietarinen wrote:
>>
>>The book is agnostic on this issue. It's starting point is that you want to
>>build an SQL database (and so there are duplicates in your results) and then
>>explains how you should do that.
>
>OK, thanks.
>
>So the answer to my question is
>"they have taken SQL as a basis _in_this_book_

Yes.

>but probably agree otherwise that duplicates should be avoided

Yes.

>and better optimisations would be obtained without duplicates"

No. In fact, in theory, all optimizations that can be done in a set-based algebra can also be done in a bag-based algebra but not the other way around.

• Jan Hidders