Re: retrieve rows in a specified order
Date: Sun, 21 Dec 2003 21:16:49 GMT
"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?
- 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 - 22:16:49 CET