Hi, MARK!
On May 14, MARK CALLAGHAN wrote:
> On Thu, May 14, 2009 at 3:09 AM, Sergei Golubchik <serg@stripped> wrote:
> > On May 13, Vyacheslav Akhmechet wrote:
> >>
> >> Suppose a given key has two parts, A and B, and I build an index on
> >> this key (by combining A and B in lexicographic order, or a similar
> >> technique). Now, suppose index_read is called, and part A is missing
> >> from the key. In this case the index is essentially useless - I need
> >> to do a full table scan. I don't see how one could implement an index
> >> to get around this.
> >>
> >> Am I misunderstanding the purpose/semantics of keypart_map?
> >
> > No, you are not. Btree indexes, indeed, cannot support this feature.
> > Bitmap indexes, I presume, can.
>
> Btrees can and do support index scans in this case. Check out index
> skip scan in Oracle.
> http://www.google.com/search?q=index+skip+scan
Yes, right.
In btree you can do an index scan, but it won't be a range as with a
prefix key.
Thanks for correcting me.
Regards / Mit vielen Grüßen,
Sergei
--
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