Re: 3 value logic. Why is SQL so special?

David Portas wrote:
> Cimode wrote:
> > A UNION equivalent an LEFT OUTER JOIN BULLSHIT!!!. A LEFT OUTER JOIN is
> > just SQL miserable way to force a presentation inspired perspective
> > into design issues that should be regulated by normalization to
> > preserve integrity. The proof is that you can do a UNION using 2
> > relations but using LEFT OUTER JOIN when dealing with relations has no
> > meaning. Consider 2 tables table1(id1, key1) and table2(id2, key2)
> >
> > Table1
> > 1, A
> > 2, B
> > 3, C
> >
> > Table2
> > 8, A
> > 10, C
> >
>
> T1{k,i1,i2} UNION (T1{k,i1} JOIN T2{k,i2})
>
> Obviously some suitable value or expression has to be supplied for i2
> on the left hand side of the UNION.

Isn't that going to run in to a problem if we infer a key for the result? With the left outer join, we can infer k as a key of the result, but with the above union we can't. (The key is {k,i1,i2}.) And we'll have more than one row for some values of k.

Wouldn't it be more like:

(T1{k,i1,i2} MINUS (T1{k} JOIN T2{k}))
UNION (T1{k,i1} JOIN T2{k,i2})

(Not sure if I got the syntax right.) I still don't see how to do key inference correctly on the above, but at least it won't have multiple rows for some k values.

Marshall Received on Sat Sep 16 2006 - 20:43:43 CEST