Re: Informal Survey #1 -- joins on foreign keys

On 1 oct, 19:09, Rob <rmpsf..._at_gmail.com> wrote:
> First, let me qualify my interests. I am primarily interesested in the
> mechanics of
> relational database management, not the semantics. I am interested in
> the evaluation
> of sql queries without regard to their meaning.
A contradiction in your statement. You seem interested in relational management but not enough to put some effort to understand what it is about.

> 1. without racking  your brain or searching the archives of your
> previous work, does
> your gut feeling tell you have ever authored or seen an sql query in
> which two relations
> were joined on a foreign key in each?
Yes. No big deal.

> 2. using your knowledge and understanding of (any) relational algebra,
> is a join
> between two relations on a foreign key in each ever meaningful? (Keep
> in mind
> the definition of the domain of a foreign key.)
None particular.

> 3. in the semantic realm you use to "think about" relational databases
> (i.e., E-R,
> facts, etc.), does a join between two relations on a foreign key in
> each make sense?
JOIN is a relational operator. It can be used between any relation column subset.

> I request that you spend at least 10 minutes thinking about this
> before you flame
> me.
No flames. Just simple answers as you requested.
> Rob
Received on Sat Oct 01 2011 - 20:34:09 CEST