🚀 go-pugleaf

"Craig Stuntz [TeamB]" <cstuntz@nospamplease.com (but use vertexsoftware to
email)> wrote in message
news:MPG.184c1b6154274d7b98a260@newsgroups.borland.com...
> In article <3de24925@newsgroups.borland.com>, eddielee@tropicsoft.com
> says...
> > I don't see what the difference between a descending and ascending index
is
> > in this situation. I think the key point is that there be an index so
that
> > each row doesn't have to be read to find the maximum value.
> >
> IB can use a DESCENDING INDEX to find a MAX value, but it can't use
> an ASCENDING INDEX to find a MAX.  (Conversely, it can use an ASCENDING
> INDEX for a MIN value, but not a DESCENDING INDEX.)
>
> The reason is that IB prefix-compresses the index, and it would have
> to walk the entire index to get to the max node.  It would then have to
> determine if that row (or rows) was visible to the current transaction,
> and "back out" if not.

If the index is sorted based on the index value, which seems pretty natural
so that a particular record can be found easily based on its index, then
going to the last record of the index of an ascending index will give the
max value.