Re: [SQL] Howto to force NULL rows at the bottom ?

> After further thought I think the goal of making explicit sort order
> always match btree index results is unreachable, because the explicit
> sort hasn't got enough information.  All it has is an operator ID, and
> that's about all it can possibly have, at least in the "USING operator"
> case.  But btree ordering doesn't depend on an operator ID, it depends
> on an opclass.  The counterexample goes like this: I could easily make
> two different opclasses, "int_forward" and "int_reverse", that both work
> on int4 data but produce opposite btree sort orders.  They're even built
> from the same operators, just lined up differently.  Now, how shall an
> explicit sort decide which btree ordering to conform to?  Indeed, if
> I make two indexes on the same table using the two opclasses, it's not
> even predictable which ordering an index-driven sort will return.
> 
> This counterexample is a bit farfetched of course, but it shows that
> there is no theoretically-pure answer.  We have to make some unprovable
> assumptions about what to do.

But if we have an operator, shouldn't we just look for < and > and use
them if we have those symbols?  Seems like it would be better than what
we have, if not perfect.

--  Bruce Momjian                        |  http://www.op.net/~candle maillist@candle.pha.pa.us            |  (610)
853-3000+  If your life is a hard drive,     |  830 Blythe Avenue +  Christ can be your backup.        |  Drexel Hill,
Pennsylvania19026