Re: retrieve rows in a specified order

From: Marshall Spight <mspight_at_dnai.com>
Date: Sun, 21 Dec 2003 21:16:49 GMT
Message-ID: <55oFb.12594$VB2.23160@attbi_s51>

"Paul" <paul_at_not.a.chance.ie> wrote in message news:MPG.1a5017f197c16857989855_at_news1.eircom.net...

> At least that's my understanding of one of the reasons why the concept
> of row number is out for RDBMS's - anyone disagree?

My thoughts on why no row order:

Relations are based on set theory. Members in sets are unordered.
Adding implicit ordering information would give you nothing that you don't already have with explicit ordering. Except implicit ordering would require a bunch of new operations, like the aforementioned MOVE UP, MOVE DOWN, etc. That is, it would add complexity but no power.

That said, it would be nice if maintaining a single, integer-valued explicit total ordering was as simple as it is with a list.

Note how many qualifiers I had to put in the above. If you want table ordering that is *any* of: multiple orders, non-integer valued, or partial, a list will fail you, whereas a relation covers all of these cases with the same ease.

Marshall Received on Sun Dec 21 2003 - 15:16:49 CST