Re: SQL (was: Why using "Group By")

"Mikito Harakiri" <mikharakiri_at_ywho.com> wrote in message news:Y58ca.24$wV5.164_at_news.oracle.com...
> "Bob Badour" <bbadour_at_golden.net> wrote in message
> news:NY7ca.4$GY2.112751_at_mantis.golden.net...
> > > In SQL there is a "select" clause, it corresponds to projection
> operation
> >
> > Actually, it is a combination of extend, project and summarize.
>
> Trivially so for "extend" being inverse to "project". Not sure about
> summarize. Summarize result extends the input relation with additional
> "aggregate" column, and projecting the input relation to the "group by"
> column at the same time. In the set symantics you have to say no more, but
> in the bug semantics I have to apply restriction to make rows "distinct".

Were the latter semantics a freudian slip? Technically SQL's select list isn't even project unless it includes distinct or group by, but I didn't want to seem too contrary.

> > Table closure actually. Have you ever considered that SQL's cartesian
> > product followed by restriction, if handled correctly, is a poor cousin
of
> a
> > relational join? Have you ever noted that it forces the effort to
identify
> > the common columns onto the user?
>
> Why is it such a big deal?

Forcing users to perform easily automated tasks? Do you really have to ask?

> > > Subquery
> > > into the "select" clause, as we saw, is a nice way to express
> aggregation.
> > > Chris Date considers scalar subqueries disgusting, but are they
really?
> >
> > Implicit conversion from a table to a scalar? Yeah, I agree they are
> > disgusting.
>
> You wouldn't agree that any aggregate operation is a conversion of a
> table/collection to a single value?

You wouldn't agree that any aggregate operation is explicit?

> > > Finally, a
> > > subquery in the "where" clause allows us to express logical
quantifiers.
> > > This is as much SQL as I'm able to digest so far, but I wasn't
> > disappointed.
> >
> > Without logical identity, the first question that comes to mind is:
> Logical
> > quantifiers of what exactly?
>
> This idea needs more maturity, granted.

Unfortunately, duplicates are in SQL to stay. Received on Fri Mar 14 2003 - 03:52:57 CET