Re: 4 the FAQ: Are Commercial DBMS Truly Relational?
Date: Sun, 10 Oct 2004 13:53:41 -0400
Message-ID: <GoadnX8cvMul6vTcRVn-iw_at_comcast.com>
"Marshall Spight" <mspight_at_dnai.com> wrote in message news:xMcad.156343$wV.96061_at_attbi_s54...
> This is essentially a right outer join, but there are
> no nulls in the result.
>
> I believe TTM has such an operator. I should probably
> go back and read about it.
Thanks. I think I get it. It smells a little more "relational" to me than the SQL "group by". Probably a good thing. And, unlike the SQL "group by", it has a definable inverse.
Two points: first, the empty set carries the same kind of information that a NULL in anouter join does, without being a NULL.
Second, in order to accept the result as a relation, you have to allow
domains that are relations. Since Date does this, it's consistent with the
direction he's going in.
It looks interesting. Thanks for clearing it up.