Re: Issues with the logical consistency of The Third Manifesto

From: Marshall Spight <mspight_at_dnai.com>
Date: Tue, 16 Nov 2004 16:47:27 GMT
Message-ID: <zaqmd.39461$V41.14551@attbi_s52>

"Paul" <paul_at_test.com> wrote in message news:4199ba2f$0$33633$ed2619ec_at_ptn-nntp-reader02.plus.net...
>
> I think that standard SQL blurs the line between types and relations a
> bit with its equality test. For example:
>
> SELECT * FROM t WHERE a = b
>
> The equals is seen more as part of the relational algebra rather than
> the type algebra. Why can't WHERE clauses take boolean values like this?:
>
> SELECT * FROM t WHERE equals(a,b)
>
> Maybe it's because SQL doesn't really have proper support for
> user-defined types yet.

It's long bugged me that the relational algebra has such seemingly non-algebraic things in it as restrict and project.

Marshall Received on Tue Nov 16 2004 - 10:47:27 CST