Re: <OR> predicate?
Date: Wed, 29 Sep 2010 10:22:12 -0700 (PDT)
Message-ID: <5d69bb34-d756-4225-baf2-9a5c65241882_at_d25g2000yqc.googlegroups.com>
On 29 sep, 16:40, Vadim Tropashko <vadim..._at_gmail.com> wrote:
> A bulk of discussion is devoted to introduction of PLUS predicate, but
> then, I fail to see how given the two relations EMP and PLUS one can
> express the query "give employee departement numbers wit salary
> totals" in relational algebra, and, therefore in A-algebra.
I think PLUS is of no use to you in this situation.
The function/relation you need to come to the aggregate results is a function that maps a relation {1 2 3} (deliberately using sloppy shorthand here) onto, e.g. if the aggregation operation is addition, the number 6. The relation that represents the invoked aggregate operator (SUM, COUNT, ...) in question, that is.
Or is that not the problem ? Received on Wed Sep 29 2010 - 19:22:12 CEST